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DOCUMENT RESUME ED 411 297 TM 027 312 AUTHOR Patsula, Liane N.; Steffen, Mandred TITLE Maintaining Item and Test Security in a CAT Environment: A Simulation Study. Laboratory of Psychometric and Evaluative Research Report No. 309. PUB DATE 1997-03-00 NOTE 32p.; Paper presented at the Annual Meeting of the National Council on Measurement in Education (Chicago, IL, March 25-27, 1997). PUB TYPE Reports - Evaluative (142) Speeches/Meeting Papers (150) EDRS PRICE MF01/PCO2 Plus Postage. DESCRIPTORS *Adaptive Testing; *Computer Assisted Testing; *Item Banks; *Multiple Choice Tests; Probability; Simulation; Test Construction; Test Items IDENTIFIERS *Test Security ABSTRACT One challenge associated with computerized adaptive testing (CAT) is the maintenance of test and item security while allowing for daily testing. An alternative to continually creating new pools containing an independent set of items would be to consider each CAT pool as a sample of items from a larger collection (referred to as a VAT) rather than as a permanent collection of items. This research investigated the viability of creating overlapping CAT pools from a static VAT by sampling items with replacement. The VAT used in this simulation consisted of approximately 5,000 precalibrated verbal multiple-choice items. Item pools were created, and simulations were performed to configure each of these item collections into CAT pools and to estimate the proportion of examinees at each of 13 ability levels that were expected to see each item. Probabilities of administration were computed for each item and different numbers of examinees and item pools were simulated. As the number of pools increased, their quality decreased, and the proportion of items reaching the retirement threshold for test items decreased. As more pools were created, the potential for control increased. Results support the use of a VAT system as a way of drawing a compromise between test quality and test security. (Contains five figures, six tables, and five references.) (SLD) ******************************************************************************** Reproductions supplied by EDRS are the best that can be made from the original document. ********************************************************************************

Transcript of DOCUMENT RESUME Patsula, Liane N.; Steffen, Mandred PUB ... · DOCUMENT RESUME. ED 411 297 TM 027...

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DOCUMENT RESUME

ED 411 297 TM 027 312

AUTHOR Patsula, Liane N.; Steffen, MandredTITLE Maintaining Item and Test Security in a CAT Environment: A

Simulation Study. Laboratory of Psychometric and EvaluativeResearch Report No. 309.

PUB DATE 1997-03-00NOTE 32p.; Paper presented at the Annual Meeting of the National

Council on Measurement in Education (Chicago, IL, March25-27, 1997).

PUB TYPE Reports - Evaluative (142) Speeches/Meeting Papers (150)EDRS PRICE MF01/PCO2 Plus Postage.DESCRIPTORS *Adaptive Testing; *Computer Assisted Testing; *Item Banks;

*Multiple Choice Tests; Probability; Simulation; TestConstruction; Test Items

IDENTIFIERS *Test Security

ABSTRACTOne challenge associated with computerized adaptive testing

(CAT) is the maintenance of test and item security while allowing for dailytesting. An alternative to continually creating new pools containing anindependent set of items would be to consider each CAT pool as a sample ofitems from a larger collection (referred to as a VAT) rather than as apermanent collection of items. This research investigated the viability ofcreating overlapping CAT pools from a static VAT by sampling items withreplacement. The VAT used in this simulation consisted of approximately 5,000precalibrated verbal multiple-choice items. Item pools were created, andsimulations were performed to configure each of these item collections intoCAT pools and to estimate the proportion of examinees at each of 13 abilitylevels that were expected to see each item. Probabilities of administrationwere computed for each item and different numbers of examinees and item poolswere simulated. As the number of pools increased, their quality decreased,and the proportion of items reaching the retirement threshold for test itemsdecreased. As more pools were created, the potential for control increased.Results support the use of a VAT system as a way of drawing a compromisebetween test quality and test security. (Contains five figures, six tables,and five references.) (SLD)

********************************************************************************

Reproductions supplied by EDRS are the best that can be madefrom the original document.

********************************************************************************

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Maintaining Item and Test Security in a CAT Environment:A Simulation Study 1'2

Liane N. Patsula3University of Massachusetts at Amherst

Manfred Steffen4Educational Testing Service

'Paper presented at the National Council on Measurement in Education, Chicago, IL, March 1997.2Laboratory of Psychometric and Evaluative Research Report No. 309. University of Massachusetts at Amherst,

School of Education.3This research was initiated while the first author was a summer intern with the Graduate Research Examination

Program at Educational Testing Service.4The authors would like to thank Ronald Hambleton and Charlie Lewis for their comments on an earlier draft of this

paper.

BEST COPY MAMA LE

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Test Security 2

Maintaining Item and Test Security in a CAT Environment:

A Simulation Study

Liam N. Patsula

University of Massachusetts, Amherst

Manfred Steffen

Educational Testing Service

As is evident in the measurement literature of the past ten years, the use of computerized

adaptive testing (CAT) by credentialing agencies to measure knowledge and skills in a particular

domain has become increasingly prominent. This can be attributed to the many advantages of

CAT. From an assessment standpoint, computerized adaptive tests are more efficient than

conventional paper-and-pencil (P&P) tests, typically requiring about halfas many items to attain

an equivalent level of precision. This is due to the fact that questions in a computerized adaptive

test are tailored to an individual examinee's ability level. In addition, CAT offers advantages to

test developers of improved test reliability, improved test security and data collection, better

opportunity to control cheating, and cost savings with regard to printing and shipping.

Advantages to test takers include the convenience and flexibility of scheduling an appointment to

test, year-round testing, immediate knowledge of scores, faster score reporting service, and

potentially shorter tests (Wainer, Dorans, Flaugher, Green, Mislevy, Steinberg, & Thissen, 1990).

However, despite the many stated advantages of CAT, there are also some challenges to

be confronted in implementing CAT. These include such practical issues as selecting the first3

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item, choosing the stopping rule, scoring adaptive tests, administering items belonging to sets,

controlling item exposure and overlap, providing item review to candidates, dealing with item

omissions, allowing for incomplete tests, developing CAT pools, maintaining CAT pools, and

complying with disclosure requirements (Mills & Stocking, 1995). One such challenge that is

the focus of this study is the maintenance of item and test security while allowing for daily

testing. The major challenge facing large-scale CAT programs that test daily is to redefine item

and test security with regard to the access of items to examinees.

It is important to emphasize that CAT does not necessarily present the new security

challenge, but rather it is the daily access to testing. One could potentially conceive of thousands

of students gathering in a gymnasium, one Saturday morning, each provided with his or her own

computer to take a CAT. There would only need to be one modest sized item pool, perhaps not

very much larger than the length of the P&P version of the exam. This would avoid many of the

CAT security issues. The real challenge to CAT test security is the daily access to testing or

what some call continuous testing.

Test security issues are not unique to CAT. To lead one to believe that the concern over

test security is new with the advent of CAT is misleading. P&P testing programs have and have

always had security concerns. Indeed, the driving force for parallel forms is to address security

concerns. To insure fairness to examinees by insuring that test forms are equivalent, P&P testing

programs need to equate test forms as new forms are introduced at each administration. In

addition, there are security concerns over pretest items. Including pretest items in a test causes

these items to be exposed or known to candidates, and possibly to coaching schools and future

candidates. An item need only be exposed to one person for its security to be sacrificed. The

concern over pretest items also carries over to CAT. (As an aside, Sheehan and Mislevy (1994)

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and Billeaud and Steffen (1996) have been examining ways to avoid the need for pretesting items

by calibrating item with little or not data using collateral information.) Security issues are not

unique to CAT.

There are three main concerns relating to test security whether within a CAT or P&P

environment repeaters, cheaters, and coaching schools. The first concern is that of repeaters,

those students who choose to take the test more than once. If the same items appear on multiple

tests, repeaters have an advantage of foreknowledge of items. A second concern involves

cheaters. In a P&P environment, this refers to those who copy answers from neighboring

examinees. In a CAT environment, while it is harder to copy from a neighbor since each

examinee would most likely be seeing a different test and examinees are seated in separate

cubicles, candidates can share the items they saw with a candidate scheduled to take the test in

the future. In either the P&P or CAT environment, examinees from one time zone could

communicate via the internet, fax, or phone sharing the items that appeared on their test.

However, this would be more prevalent with P&P programs that use only a single form. Again,

this would give the second candidate the advantage of foreknowledge of items. The last concern

and perhaps the largest concern involves coaching schools. In cases where coaching schools

have examinees report to them the items they were administered, these items can then be shared

with future candidates and the validity of the test has been compromised. Any sharing of items is

cheating, as each candidate signs an agreement stating they will not disclose any items. Still, the

practice is known to go on.

Historically, large scale P&P testing programs have maintained test security by closely

guarding access to test items by regularly introducing new forms and judiciously reusing old

forms over relatively large intervals of time at small numbers of annual administrations. The

5.

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reuse of these forms was done in such a way that even if a potential examinee had foreknowledge

of a specific form; it is unlikely that the examinee would be administered the exact form at the

test session. The size of the problem was assumed to be quite small.

Now, with the daily access to item pools necessary to support large volume CAT testing,

this type of controlled access is no longer possible. Because only a finite number of precalibrated

test items are available to be administered daily; a program must reuse items and must do so in a

judicious manner to maintain test security.

One CAT analog to the P&P procedure of reusing items might be to prepare a large

number of CAT pools and rotate them in a random fashion. However, two factors need to be

considered. First, CAT pools tend to be much larger than traditional test forms, typically the

equivalent of 8-12 test forms. To attempt to parallel traditional security measures results in a

demand for new items so great that it far exceeds the financial resources of even large programs.

Thus, with a limited item supply, the number of unique pools is restricted. Second, an artifact of

CAT pools is that examinees of comparable ability tend to be administered many of the same

items. Since CATs are shorter than their P&P counterparts, this similarity can become a serious

threat to test security. With daily as opposed to quarterly testing, opportunities to recognize the

similarity of tests increases and correspondingly the probability of foreknowledge increases of

particular items.

An alternative to continually creating new pools containing an independent set of items,

would be to consider each CAT pool as a sample of items from a larger collection (subsequently

referred to as a VAT) rather than as a permanent collection of items. By sampling items with

replacement, a theoretically infinite number of overlapping CAT pools might be created. In

addition, a set of item reuse rules intended to minimize the benefit that might be expected from

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foreknowledge of a portion of the VAT could be instituted. One example of an item reuse rule

may be not to include any item in a pool that has been seen by more than 200 people in the last

two months.

The purpose of this research was to investigate the viability of creating overlapping CAT

pools from a static VAT by sampling items with replacement. Several item reuse conditions

were explored; mainly item overlap and item exposure rates. Item overlap rates refer to the

number of pools in which an item appears. Item exposure rate refers to the number of examinees

who have seen a particular item. An item is usually retired (Le., removed from future use) after it

has been seen by a certain number of examinees over some specified period of time.

To increase the generalizability of the results of this study to different size testing

programs, different annual test taking volumes were studied. In addition, it was hypothesized

that testing programs with different volumes would not require as many pools per year.

Therefore, the number of pools created per year was also manipulated. The primary research

question was: For a fixed-size VAT, if items in a CAT pool are retired under 'X' conditions and

pools are seen by 'N' examinees, how many times can the pool creation process be repeated

before the selected pool will fail to support the delivery of CATs meeting certain delivery time

constraints (e.g., one pool per week)?

Method

This section is divided into four parts: description of data, test conditions, simulation

procedure, and data analysis.

Description of Data

This section describes the simulations that were used to prepare the data for use in this

study.

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The VAT of items used in this study consisted of approximately 5,000 precalibrated

Verbal multiple-choice items. These items included both discrete items and items belonging to

sets, as well as stimuli. To use these items to study item exposure rates, it was necessary to

estimate predicted usage rates for each item. This was accomplished by creating ten pools,

consisting of approximately 450 items each, from this collection of 5,000 items. Simulations

were performed in order to configure each of these ten item collections into CAT pools and to

estimate the proportion of examinees at each of 13 ability levels that were expected to see each

item. These proportions are referred to as conditional (on ability) probabilities of administration.

As not every item in the VAT appeared in at least one of the ten pools, some items did

not have probabilities of administration (PRB's) associated with them. Thus, it was necessary to

assign conditional probabilities of administration to these items in some way. The method used

to assign PRB's to stimuli was different than that used to assign PRBs to discrete items. Each

method is presented separately.

Discrete Items. To assign a PRB vector to every discrete item in the VAT, one

simplifying assumption was made. It was assumed that the interaction of the major content area

and the difficulty parameter of the item adequately captured the PRB vector. This assumption

allowed us to associate the PRB vector of a discrete item with a certain content area and

difficulty level to another discrete item with the same content area and difficulty level.

To associate a PRB vector to every discrete item in the VAT, all of the items from the ten

pools were sorted by content area and difficulty level. The items were placed into levels of

difficulty ranging from -3.0 to 3.0 in increments of 0.5. This resulted in five content areas and 13

difficulty levels and therefore 65 (5x13) content by difficulty combinations. Where there were

less than ten items of one combination, two or more difficulty levels were aggregated. The result

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was 44 different content by difficulty combinations. An analysis of these PRB vectors indicated

our assumption was plausible, that there was significant similarity in the vectors for the items

with similar combinations of content classifications and difficulty parameters. Thus, it was

possible to assign a PRB to each discrete item in the VAT that did not appear in one of the ten

pools.

Stimuli. For the CAT algorithm under study, stimuli are not directly selected. With few

exceptions, it turns out that within every set, there are items that mirror the overall selection

characteristics of the stimulus. This fact was used to predict PRB's for stimuli. To assign PRB's

to stimuli in the VAT, several variables item in set with maximum information, item in set with

largest a estimate, and item in set with smallest c estimate were analyzed to determine which

item's PRB vector best predicted the PRB vector of the stimulus. This varied for the different

ability levels and content areas. In all cases, depending on what variable accounted for the most

variance, either the PRB vector associated with the item in the set that had the maximum

information or the item in the set with the largest a estimate was assigned to each stimulus in the

VAT. In the remainder of the study, only discrete items and stimuli were included in the VAT.

In summary, the VAT consisted of 2,978 elements with each discrete item and stimuli

have a PRB vector associated with it. The probabilities associated with discrete items depended

upon the content area and level of difficulty. The probabilities associated with stimuli depended

upon the content area and the item in the set that had the maximum information or the item in the

set with the largest a estimate was assigned to each stimulus in the VAT.

Test Conditions

The remainder of the study involved simulating 15 different test conditions for each item

reuse rule set (see Table 1). The item reuse rules are described below.

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Table 1

Summary of 15 Test Conditions

Test Condition Annual Test-TakerVolume

Number of PoolsCreated per Year

1 20,000 62 50,000 63 100,000 6

4 20,000 125 50,000 12

6 100,000 12

7 20,000 18

8 50,000 18

9 100,000 18

10 20,000 24. 11 50,000 24

12 100,000 24

13 20,000 3014 50,000 3015 100,000 30

Each test condition was defined by some combination of two factors: (1) number of pools to be

created per year and (2) annual test taking volume. The number of pools to be created per year

was chosen to be 6, 12, 18, 24, or 30. The lower number of pools to be created of 6 was chosen,

as it seemed to be the bare minimum number of pools to be used to keep item exposure rates to a

minimum. The upper number of 30 pools to be created per year was chosen to reflect what is

thought might be reasonable in practice. Second, three total test taker volumes were used:

N=20,000, 50,000, and 100,000. The lowest sample size of 20,000 was chosen to reflect the test

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taker volume of smaller testing programs and the upper sample size of 100,000 was chosen to

reflect the test taker volume of larger testing programs.

Simulation Procedure

The simulation phase consisted of creating item pools from the VAT. This involved three

steps.

Step I. Before being passed to the pool creation process, items were evaluated with

respect to each of four reuse rules. Failure to meet any one of these rules precluded the item

from being reused (i.e., included in the present pool). There was one item overlap rule and three

item exposure rules. First, concerning item overlap, an item could not be included in the present

pool if it appeared in the last pool created. For example, during the development of Pool 9, no

item from Pool 8 was considered. The purpose of this rule was to minimize the effect of

candidates who have taken the test sharing with candidates planning on taking the test.

Concerning item exposure rates, an item could not be used in the current pool if:

i) the total number of examinees who have seen the item since its introduction exceeded

10,000; or

ii) the number of examinees who have seen the item in the past four months exceeded 1,000;

or

iii) the number of examinees who have seen the item in the past two months exceeded 100,

200, 300, 400, or 500.

These numbers were chosen arbitrarily. Initially, the first two rules were to be

manipulated by increasing the numbers from 10,000 to 25,000 and 50,000; and from 1,000 to

2,000 and 3000. However, based on some preliminary analyses, very few items were seen by

more than 5,000 people and so increasing this number was not warranted. After 10,000 or more

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people saw an item, it was retired. This is to say that the item could no longer be included in

another pool and so it was removed from the VAT.

In addition, some preliminary analyses revealed that for small volumes of test-takers,

nothing was caught by the four-month rule. However, it did come into play somewhat for larger

volumes. Nevertheless, this rule was not manipulated.

Only the two-month rule was manipulated. To minimize the effect of sharing among

candidates, an item was not included in the subsequent two month pools if it had been seen by

more than 100 people. This rule was relaxed to allow up to 200, 300, 400, or 500 people to see

an item in the past two months to examine the impact of this rule on the quality.of subsequent

pools.

Step 2. Pools were created with respect to content specifications, the overlap rule, item

exposure rules, and the total pool information function. Each of these constraints had a weight

associated with it to reflect its importance. In this way, test specialists can quantitatively

prioritize the constraints. Weights varied from 5 being relatively unimportant to 60 being very

important. A summary report of rule violations and overall index of the degree to which the pool

met specifications was produced. This overall index was a total weighted deviation and was used

as an overall index of pool quality in subsequent analyses.

Step 3. The last step involved updating the cumulative pool history record. It is at this

stage that annual test taking volume was manipulated. For each item included in the current

pool, the number of examinees expected to see the item was computed. Computation of the

expected volume for each item required three pieces of information:

i) the PRB vector,

i2

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ii) a vector of weights (WTS) associated with each PRB. This vector represents the

proportion of a specified examinee population that is expected to appear at each of the

13 ability levels. A normal distribution of ability was modeled.

iii) the number of examinees to whom pool P will be administered (VOLp).

Manipulation of this number allowed us to model annual test taking volume (20,000,

50,000, and 100,000).

In summary, the volume for discrete item or stimulus j was computed as:

VOLUME./ =VOLp*E(PRB *WTS;) .

This simulation cycle was repeated 6, 12, 18, 24, and 30 times to model the number of

pools to be created per year.

Data Analysis

The data were analyzed according to the effects of the number of pools created per year

and the annual test-taking volume on the quality of pools and retirement of items. First, the

quality of the resultant pools in terms of their total weighted deviations was examined. As

described earlier, the total weighted deviation is an index of the amount of deviation there is in

the pool from the set of constraints placed upon the pool. Since it is not always possible to

satisfy all constraints simultaneously, each constraint is weighed to reflect the importance of the

constraint. Any deviation from the constraint is reflected in the total weighted deviation. As an

example, one constraint may be that the pool should consist of at least 50 but no more than 55

antonym items. This constraint might have a weight of 60 associated with it. In some instances,

perhaps due to many antonym items included in the previous pool, there may only be 48 antonym

items available for inclusion in the present pool. In this case, the deviation would be two and the

weighted deviation would be 120 (2x60). The concern was not the absolute magnitude of the

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total weighted deviation but the relative value across pools created within a year (6, 12, 18, 24, or

30 pools per year).

This total weighted deviation for each pool was plotted. An ideal situation would be to

have minimal total weighted deviations across all pools. The first irregularity of the plotted

values indicated that the number of "optimal" pools had been selected. The purpose of the

simulation cycle was to find the threshold where the violations produced an unacceptable pool.

In this context, unacceptable means that it was unlikely that a CAT design could be created that

would allow this collection of items to produce acceptable CATs. That is, at some point, the

selected pools may not adequately meet all of the constraints.

Second, the rate at which items are predicted to be retired from use (due to more than

10,000 people being administered an item) was examined. As items are reused over a number of

pools.

Results

The results are summarized according to the effects of the number of pools created per

year and the annual test-taking volume on the quality of pools and retirement of items.

Quality of Pools. Recall that only the two-month rule was manipulated. Figures 1 to 5

correspond to the total weighted deviations of pools created in a year using the two-month rule of

not including an item in a pool if more than 100, 200, 300, 400, and 500 people saw the item

within the last two months, respectively.

Upon inspection of Figure 1, it is apparent that in general, with annual test-taking

volume held constant (looking down columns), as the number of pools created per year

increased, on average, the quality of the pools decreased as is evident by larger total weighted

deviations. In general, with number of pools created per year held constant (looking across

1 4

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rows), pool quality also decreased as test-taker volume increased from 50,000 to 100,000 with

the exception of creating six pools per year. However, the same does not hold true for all

conditions when going from 20,000 to 50,000 test-takers per year. Except for the "spike" that

occurs around three months, it appears as though there are better quality pools with 20,000 than

50,000 test-takers per year when creating 24 or 30 pools per year. Also evident in Figure 1 is that

when more than six pools were created per year, pools #6, 7, or 8 had a large total weighted

deviation.

In changing the two-month rule from not including an item in a pool if more than 100

people saw the item in the last two months to 200 people, the same results hold. One marked

difference between Figures 1 and 2 is Condition 13 (30 pools created per year and 20,000 test-

takers). The diminishing pattern of the quality ofpools is more evident in Figure 2 Condition 3.

In addition, the "spikes" are not as high for all conditions in Figure 2 as compared to those in

Figure 1.

Figures 3-5 show the same patterns as Figures 1 and 2 with the exception of the

conditions with a test-taker volume of 20,000 people per year. In these cases, test quality appears

to be as good or better with 100 versus 300, 400, or 500 people two-month rule. In addition, as

the two-month rule shifts from 200 to 500 people, the spikes begin to flatten.

Overall, as the two-month rule is changed from 100 to 500 people, the quality of the

pools seemed to increase with the exception of the lowest test-taking volume of 20,000 where

quality diminished.

Retirement of Items. Recall that an item was retired if more than 100,000 people saw the

item since its inception. Tables 2 to 6 correspond to Figures 1 to 5. These tables provide the

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percent of the total number of items seen by different numbers ofpeople and the total number of

items seen at the end of the year for different test-taking volumes.

Regardless of the two-month rule, as the number of pools created per year increased, the

total number of items used increased for all annual test-taking volumes (see Tables 2-6). As

well, as the annual test-taking volume increased, the total number of items seen by people within

a year also increased. This was true regardless of the number of pools created per year or the

two-month rule (see Tables 2-6). In addition, as the annual test-taking volume increased, there

was an increase in the percentage of total items seen by a larger number of people. For example,

in Table 6, with six pools created per year, only 4.9% as opposed to 71.4% of the items were

seen by between 2,500-4,999 people with annual test-taking volumes of 20,000 and 100,000,

respectively.

In general, as both the number of pools created per year and the annual test-taking volume

increased, there was an increase in the total number of items exposed within the year. Interesting

to note is that only in Condition 3 did items need to be retired six pools created per year with an

annual test-taking volume of 100,000. Note however, that this was only 0.7% of the total

number of items used in a year.

Discussion

The obtained results are relatively consistent with expectations. First, as the number of

pools increases, the quality of pools decreases. This is likely due to the fact that limits were

imposed on the proportion of elements from each pool that could be used in any given future

pool. Second, as the number of pools increases, the proportion of items reaching (or even

nearing) the retirement threshold decreases. Third, as volumes increase, pool quality again

decreases. This results from the increase in the number of elements that are frozen from use by

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Test Security 16

the two-month, four-month, and total volume thresholds. Additionally, since higher information

items tend to be selected more frequently, subsequent pools will tend to be created from an

available item collection with lower average information.

The spikes that occur are likely the result of demands on the VAT, with respect to

content, that are incongruent with the content composition of the VAT. More specifically, they

are due to the complex interaction of item difficulty and item information with item content.

Since we did not balance the psychometric characteristics across content strata, the occurrence of

these spikes was inevitable. The only question was when they would appear and the periodicity

of the occurrence. It should be kept in mind that these spikes resulted from a static VAT. That is

a fixed collection of elements was manipulated throughout. Thus, if the VAT were

supplemented at the point where the spikes are predicted to occur, their appearance could be

averted. Furthermore, the consistency of pool quality between spikes indicates that several

moderate infusions of elements may suffice to maintain pool quality. That is, it is not necessary

to augment the VAT before each pool is developed.

Tables 2-6 clearly indicate that the ability to control the use of items is dependent on the

number of pools developed. The more pools created, the higher the potential for control.

Conversely, as the number of pools developed is decreased, the larger the number of examinees

that interact with each pool and the less control is available for managing exposure of individual

items. This relates directly to the balancing act of item security. If the goal is to minimize the

exposure of each item in small windows of time and reuse items over large windows of time, this

is best accomplished by creating many pools per year. However, if the goal is to obtain maximal

exposure in short windows of time and then retire items, this is best achieved by creating fewer

pools per year.

'7

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Test Security 17

Taken together, these results seem to show some promise for the viability of managing

item security. By manipulating the number of pools developed per year, and manipulating the

reuse of items across pools and time, the rate exposure of items can be explicitly manipulated.

Summary

Concerns over test security are always present in large-scale testing programs because

breaches in test security impact on validity. But, in a CAT environment, there many need to be a

balancing of test security and test quality. As seen in this study, increasing test quality often

comes with a decrease in test security. There are always trade-offs to be made.

The concept of using a VAT is only one way to address item and test security concerns.

It is not necessarily the best way, but it does offer certain advantages such as controlling item

exposure rates by imposing item reuse and item overlap rules. Another distinct advantage of

maintaining item test security using a VAT is that it is a preventative approach to minimizing the

benefit that might be expected from foreknowledge of items by certain examinees. Other

methods, such as person-fit indices (Davis & Lewis, 1996), are more post-hoc approaches to

addressing test security. Person-fit indices allow one to detect "cheaters" after the administration

of the test. Cheaters may be detected by uncovering the fact that they copied their answers from

the people beside them or they may be detected by unaccountable gains when they repeat the test.

Another alternative includes two-stage testing.

The results obtained in this study give evidence to support the use of a VAT system as

one way of drawing a compromise between test quality and test security. However, this study of

examining a VAT system was by no means exhaustive. For example, this study could be

expanded by examining the effects of different ability distributions of candidates and different

.0 8

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Test Security 18

time windows on the quality of pools. In addition, one could determine what portion of the

VAT becomes deficient (e.g., certain content areas or level of difficulty of items).

While the generalizability of the specific results obtained from study may be limited, the

possibility of the use of the sampling with replacement model seems to be a promising alternative

to traditional vault-like security procedures.

References

Billeaud, K., & Steffen, M. (1996, April). Collateral information in item calibration.

Paper presented at the meeting of the National Council on Measurement in Education, New

York.

Davis, L. A., & Lewis, C. (1996, April). Person-fit indices and their role in the CAT

environment. Paper presented at the meeting of the National Council on Measurement in

Education, New York.

Mills, C. N., & Stocking, M. L. (1995, August). Practical issues in large-scale high-

stakes computerized adaptive testing (Research Report 95-23). Princeton, NJ: Educational

Testing Service.

Sheehan, K., & Mislevy, R. J. (1994, April). A tree-based analysis of items from an

assessment of basic mathematics skills (Research Report 94-14). Princeton, NJ: Educational

Testing Service.

Wainer, H., Dorans, N. J., Flaugher, R., Green, B. F., Mislevy, F. J., Steinberg, L., and

Thissen, D. (1990). Computerized adaptive testing: a primer. Hillsdale, NJ: Lawrence Erlbaum

Associates.

'9

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Test Security 19

Table 2

Percent of Total Number of Items Seen by Different Numbers of People and the Total Number of ItemsSeen at the End of the Year for Different Test- Taking Volumes Using the 100 Two-No. ofPools

/Year

AnnualTest-Taker

Volume

Number of People

Total,0-99 100-499 500-999 1,000-2,499 2,500-4,999 5,000-9,999 10,000+20,000

6 50,000 0.8 1.8 15.0 43.1 38.5 0.9 0.0 1082100,000 0.8 1.1 1.5 10.1 71.1 14.6 0.7 110520,000 0.5 6.0 91.1 2.4 0.0 0.0 0.0 1719

12 50,000 0.5 1.3 48.1 38.5 11.6 0.0 0.0 1894100,000 0.5 1.2 10.5 41.2 44.0 2.8 0.0 190320,000 0.5 8.5 86.5 4.5 0.0 0.0 0.0 1925

18 50,000 0.4 1.6 57.0 31.2 9.9 0.0 0.0 2040100,000 0.4 1.3 11.6 45.8 36.5 4.3 0.0 205620,000 0.5 18.4 77.5 3.6 0.0 0.0 0.0 2105

24 50,000 0.4 2.3 61.4 30.4 5.5 0.0 0.0 2310100,000 0.4 1.2 22.5 40.2 34.6 1.1 0.0 234720,000 0.5 24.8 69.4 5.3 0.0 0.0 0.0 2246

30 50,000 0.4 2.9 62.4 31.8 2.5 0.0 0.0 2554100,000 0.4 1.2 31.3 33.4 33.6 0.2 0.0 2954

Table 3Percent of Total Number of Items Seen by Different Numbers of People and the Total Number of ItemsSeen at the End of the Year for Different Test - Taking Volumes Using the 200 Two-Month RuleNo. ofPools

/Year

AnnualTest-Taker

Volume

Number of People

Total0-99 100-499 500-999 1,000-2,499 2,500-4,999 5,000-9,999 10,000+20,000 0.9 3.4 75.4 18.8 1.6 0.0 0.0 1033

6 50,000 0.8 1.8 14.4 43.4 58.7 0.9 0.0 1075100,000 0.8 1.1 1.5 10.1 71.3 14.6 0.7 110420,000 0.7 9.5 81.7 8.1 0.0 0.0 0.0 1486

12 50,000 0.5 1.5 45.7 40.1 12.2 0.0 0.0 1824100,000 0.5 1.2 10.4 41.1 44.0 2.8 0.0 189420,000 0.5 14.2 75.7 8.9 0.8 0.0 0.0 1863

18 50,000 0.5 2.3 52.9 34.2 10.2 0.0 0.0 1956100,000 0.4 1.2 11.6 45.8 36.6 4.4 0.0 204420,000 0.4 26.1 67.3 5.5 0.7 0.0 0.0 2203

24 50,000 0.5 3.2 54.6 35.8 5.9 0.0 0.0 2183100,000 0.4 1.4 20.8 41.3 35.0 1.1 0.0 231020,000 0.4 32.9 61.8 3.7 1.1 0.0 0.0 2465

30 50,000 0.4 3.5 59.0 30.5 6.6 0.0 0.0 2303100,000 0.4 1.3 30.2 33.3 34.5 0.2 0.0 2550

20EST COPY AVAILABLE

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Test Security 20

Table' 4Percent of Total Number of Items Seen by Different Numbers of People and the Total Number of ItemsSeen at the End of the Year for Different Test- Taking Volumes Using Two -MonthNo. ofPools

/Year

AnnualTest-Taker

Volume

-Number of People

Total0-99 100-499 500-999 1,000-2,499 2,500-4,999 5,000-9,999 10,000+

20,000 0.9 4.1 72.0 21.3 1.6 0.0 0.0 9986 50,000 0.8 1.8 13.6 43.9 38.9 0.9 0.0 1070

100,000 0.8 1.1 1.5 10.2 71.1 14.6 0.7 110220,000 0.6 12.8 72.0 14.0 0.6 0.0 0.0 1435

12 50,000 0.5 1.5 42.4 42.5 13.1 0.0 0.0 1766100,000 0.5 1.2 8.6 42.2 44.7 2.8 0.0 186820,000 0.4 15.1 77.2 5.1 2.2 0.0 0.0 2031

18 50,000 0.5 2.5 47.4 38.6 11.0 0.0 0.0 1852100,000 0.5 1.4 9.9 46.2 37.6 4.5 0.0 199820,000 0.4 25.9 69.6 2.4 1.7 0.0 0.0 2331

24 50,000 0.5 3.7 57.5 29.1 9.3 0.0 0.0 2092100,000 0.4 1.5 20.1 39.8 37.0 1.2 0.0 226820,000 0.4 31.7 64.3 2.0 1.6 0.0 0.0 2535

30 50,000 0.4 3.9 60.0 26.1 9.4 0.2 0.0 2253100,000 0.4 1.6 29.9 31.8 36.0 0.2 0.0 2498

Table 5Percent of Total Number of Items Seen by Different Numbers of People and the Total Number of ItemsSeen at the End of the Year for Different Test-Taking Volumes Using the 400 Two-Month RuleNo. ofPools

/Year

AnnualTest-Taker

Volume

Number of People

Total0-99 100-499 I 500-999 1,000-2,499 2,500-4,999 5,000-9,999 10,000+20,000 1.0 4.2 67.7 23.4 3.7 0.0 0.0 968

6 50,000 0.9 1.5 11.9 45.1 39.7 0.9 0.0 1060100,000 0.8 1.1 1.3 9.7 71.4 14.7 0.7 109720,000 0.6 13.1 72.5 12.6 1.2 0.0 0.0 1539

12 50,000 0.6 1.7 35.3 48.3 14.1 0.0 0.0 1670100,000 0.5 1.4 5.6 43.5 46.1 2.9 0.0 182620,000 0.4 15.3 78.0 4.1 2.2 0.0 0.0 2048

18 50,000 0.5 2.6 47.5 38.2 10.9 0.4 0.0 1806100,000 0.5 1.5 9.0 44.5 40.0 4.5 0.0 196020,000 0.4 26.7 68.9 2.4 1.6 0.0 0.0 2363

24 50,000 0.4 3.6 55.4 31.6 8.6 0.3 0.0 2062100,000 0.5 1.5 19.7 37.1 40.1 1.2 0.0 219520,000 0.4 34.5 61.9 1.8 1.4 0.0 0.0 2672

30 50,000 0.4 3.3 65.7 22.3 7.7 0.6 0.0 2378100,000 0.4 2.0 25.4 35.6 34.1 2.5 0.0 2319

21

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Test Security 21

Table 6Percent of Total Number of Items Seen by Different Numbers of People and the Total Number of ItemsSeen at the End of the Year for Different Test- Taking Volumes Usin the 500 Two -MonthNo. ofPools

/Year

AnnualTest-Taker

Volume

Number of People

Total0-99 100-499 500-999 1,000-2,499 2,500-4,999 5,000-9,999 10,000+20,000 0.9 4.2 71.0 19.1 4.9 0.0 0.0 1005

6 50,000 0.9 1.5 10.3 46.5 39.9 1.0 0.0 1037100,000 0.8 1.1 0.9 10.4 71.4 14.7 0.7 109720,000 0.5 13.6 77.1 6.7 2.1 0.0 0.0 1710

12 50,000 0.7 2.0 37.1 40.3 19.4 0.5 0.0 1508100,000 0.6 1.5 6.0 41.0 40.2 10.7 0.0 163820,000 0.4 15.5 78.8 2.9 2.4 0.0 0.0 2121

18 50,000 0.5 2.5 49.1 35.3 11.7 0.8 0.0 1811100,000 0.5 1.4 7.2 45.8 40.5 4.6 0.0 192920,000 0.4 26.4 69.6 1.9 1.7 0.0 0.0 2385

24 50,000 0.4 3.6 59.7 29.1 6.6 0.7 0.0 2167100,000 0.5 1.7 16.9 41.7 35.6 3.6 0.0 210420,000 0.4 38.6 58.4 1.6 1.1 0.0 0.0 2764

30 50,000 0.4 3.6 68.1 22.2 4.6 1.1 0.0 2487100,000 0.5 2.0 23.1 37.5 31.2 5.8 0.0 2240

2 2

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Page 26: DOCUMENT RESUME Patsula, Liane N.; Steffen, Mandred PUB ... · DOCUMENT RESUME. ED 411 297 TM 027 312. AUTHOR Patsula, Liane N.; Steffen, Mandred TITLE Maintaining Item and Test Security

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Page 27: DOCUMENT RESUME Patsula, Liane N.; Steffen, Mandred PUB ... · DOCUMENT RESUME. ED 411 297 TM 027 312. AUTHOR Patsula, Liane N.; Steffen, Mandred TITLE Maintaining Item and Test Security

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Page 28: DOCUMENT RESUME Patsula, Liane N.; Steffen, Mandred PUB ... · DOCUMENT RESUME. ED 411 297 TM 027 312. AUTHOR Patsula, Liane N.; Steffen, Mandred TITLE Maintaining Item and Test Security

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