16a. Accessing Data: Means in SPSS ®. 16a. Accessing Data: Means in SSPS ® 1 Prerequisites...

16a. Accessing Data: Means in SPSS®

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16a. Accessing Data: Means in SSPS®

Prerequisites• Recommended modules to complete before viewing

this module 1. Introduction to the NLTS2 Training Modules 2. NLTS2 Study Overview 3. NLTS2 Study Design and Sampling NLTS2 Data Sources, either

• 4. Parent and Youth Surveys or• 5. School Surveys, Student Assessments, and Transcripts

9. Weighting and Weighted Standard Errors

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Prerequisites• Recommended modules to complete before viewing

this module (cont’d) NLTS2 Documentation

• 10. Overview• 11. Data Dictionaries• 12. Quick References

Accessing Data• 14a. Files in SPSS• 15a. Frequencies in SPSS


Overview Purpose Exploring existing data

• Means• Comparative means

Weights Closing Important information

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NLTS2 restricted-use data• NLTS2 data are restricted.• Data used in these presentations are from a

randomly selected subset of the restricted-use NLTS2 data.

• Results in these presentations cannot be replicated with the NLTS2 data licensed by NCES.

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Purpose• Learn to

Run simple statistical procedures• Means• Comparative means

Watch for• Missing values• n’s• Weighted vs. unweighted data

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Means• How to run means• Means are run on continuous variables such as

Number of months Income Age Test scores.

• SyntaxDESCRIPTIVES VARIABLES=ndaAP_w /STATISTICS=MEAN MIN MAX.

7These results cannot be replicated with full dataset; all outputin modules generated with a random subset of the full data.


Means• From menu

Analyze: Descriptive Statistics: Descriptives Select options and uncheck “Std Deviation” in pop-up box.

• Important: Although they print by default, do not use standard deviations (or optional standard errors) from this procedure. These data are from a stratified sample, so standard errors are not

calculated correctly in this procedure. Standard errors in this procedure assume a simple random sample,

not a complex sample.• More about this later.



Means



Comparative means• As with frequencies, comparative means can be run in a single

step.• The by- (or independent) variable must be categorical.• Reminder: Do not include the standard deviation in statistics.• Syntax

MEANS TABLES=ndaAP_w BY na_age4 /CELLS MEAN COUNT.



Comparative means• From menu

Analyze: Compare Means: Means Locate [means variable name] in the variable list and click the right-facing

arrow to the left of the “Dependent List” box to select it.• Means variable

Locate [comparative variable name] in the list and click the right-facing arrow next to the “Independent” box.

• By-variable Click on “Options” and under “Cell Statistics” select “Standard Deviation.” Click the left-facing arrow. Click Continue. Press “OK” to run or select “Paste” to run code from syntax editor.



Comparative means



Means and comparative means: Example• Means and comparative means

Open the Wave 3 parent/youth interview file. Run means on np3NbrProbs. Run comparative means on np3NbrProbs by

W3_AgeHdr2005 and by W3_DisHdr2005. Important: If you use the “Paste” option, you will

be able to use this code again.



Means and comparative means: Example



Weights• How to weight data.• Running procedures unweighted is useful for exploratory analysis and

recommended for becoming familiar with the data. It is important to review the unweighted n’s

• However, unweighted results must never be reported.• The procedures we used to calculate frequencies, means, crosstabs, and

comparative means can be run with weights. The weighted means or percentages will be correct. The weighted standard errors will not be correct using these procedures; do

not report them.• Weighting in SPSS is a toggle.

The weight option can be turned on and off. The procedures themselves do not change.

• Weights are applied when the weight toggle is on.• Weights are not applied when the weight toggle is off.



Weights• Syntax: weight on

WEIGHT BY wt_npr1.

• Syntax: weight offWEIGHT OFF.

• Menu: weight on Select “Weight Cases” from “Data” menu. Click the “Weight Cases By” radio button. Locate [weight variable] in the list of variables. Click the right-facing arrow to select the weight. Press “OK” to run or select “Paste” to run code from syntax editor.

• Menu: weight off Select “Weight Cases” from “Data” menu. Click the “Do Not Weight Cases” radio button. Press “OK” to run or select “Paste” to run code from syntax editor.



Weights: Example• Weights: Run earlier examples with a weight.

Run means example weighted with np3Wt.• W3 parent interview weight np3wt• np3NbrProbs• np3NbrProbs by W3_AgeHdr2005 and by

W3_DisHdr2005 Turn weight off.



Weights: Example



Closing• Topics discussed in this module

Exploring existing data• Means• Comparative means

Weights• Next module

17a. Accessing Data: Manipulating Variables in SPSS

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Important information NLTS2 website contains reports, data tables, and other

project-related information http://nlts2.org/

Information about obtaining the NLTS2 database and documentation can be found on the NCES website http://nces.ed.gov/statprog/rudman/

General information about restricted data licenses can be found on the NCES website http://nces.ed.gov/statprog/instruct.asp

E-mail address: [email protected]

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http://nlts2.org/

http://nces.ed.gov/statprog/rudman/

http://nces.ed.gov/statprog/instruct.asp

16a. Accessing Data: Means in SPSS ®. 16a. Accessing Data: Means in SSPS ® 1 Prerequisites...

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