Variables, Hypotheses and Classification of Measurements

What Factors Determine How Fast a Car can go?• How much gas you give it• Whether of not the break is engaged• Number of cylinders in the engine• The terrain over which one is driving• The absence or presence of a wind• Type of tires on the car and their inflation level• Performance of the fuel injection system or

sparkplugs

Variables

• In research we call the factors that can influence something else (such as the speed of the car) a variable.

• But more specifically, these are called Independent Variables.

What is an Independent Variable?

• A variable that precedes, influences or predicts the outcome of the study.

• The researcher manipulates this variable, or in the case of preexisting variables that cannot be manipulated (sex, race, etc), selects the variable for inclusion in the study.

How to Remember

• An Independent Variable starts with the letter I.– So, I, the researcher can choose which variables to

manipulate or include in the study.– I have control of the selection or inclusion of the

Independent variables. – I = I

Dependent Variable

• In the car example, we are interested in measuring the “speed” of the car.

• The thing that we are measuring (speed) is called the dependent variable.

What is a Dependent Variable?

• The variable that the researcher measures; it is influenced by the independent variable.

• Sometimes called the outcome variable--measures the effect of whatever experiment you've performed. For example, if you're studying the effects of fertilizer on plant growth, the dependent variable might be measured as the height of the plant. (The amount of fertilizer you gave would be the independent variable.)

Independent & Dependent Variable Examples

• Independent Variable– Tire Pressure– Time spent studying– Family Income– Salary– SAT scores– Fertilizer Amount– Age– Hours employed

• Dependent Variable– Speed of the car– Grade on a test– 4-H Congress Attendance – Job Satisfaction– College Admission– Crop Yield– Church Attendance– GPA

In Practice

• Typically researchers will study one dependent variable per study but they might look at several different independent variables:– Is job satisfaction of extension agents influenced

by salary, hours worked, facilities or leadership style of the County Director?

In Practice

• The researcher determines what he/she– Wants to measure – the dependent variable– Wants to vary or include in the study – the

independent variable(s)• Often, the title of a research study will contain

the dependent and independent variables– “The Effect of Computer Aided Instruction on

Math Achievement of Algebra I students.” • Math Achievement is the Dependent Variable• Type of Instruction is the Independent Variable

A Word of Caution

• In identifying independent variables students often get confused with distinguishing between the independent variable and the levels of the independent variable.

• A student may claim there are three independent variables, when there is only one independent variable with three levels– See the next slide

Levels of Independent Variables

• A teacher is doing a study of Instructional Methods.– One class was taught only with lecture and no visuals– Another class was taught using the book and worksheets– A third class was taught only using PowerPoint

• In this example there is only one independent variable – Instructional Methods; but there are three levels of that variable.

One more example

• A researcher wanted to identify how to increase response rates to surveys.– 100 people received a survey from him with no incentive

to respond– Another 100 received a survey with a dollar bill inside– Another 100 received a survey with instructions that all

respondents would be entered in a drawing for $100– Another 100 received a survey with a coupon for a free

Chick-fil-a sandwich inside.

• The research compared the response rates

See the questions about this study on the next slide!

Questions about the Last Slide

• Is there one or more independent variables?– There is only one independent variable

• What is the independent variable?– Type of incentive received

• How many levels of the independent variable are there?– Four (none, $1, money drawing, food coupon)

• What is the dependent variable?– Response rate

What are Confounding Variables?

• A variable, other than those being explored in a given study, that affects the research outcomes.

• There are three types:– Intervening: other variables such as motivation or

intelligence are at play (our text calls this a moderator variable)

– Organismic: physical traits such as poor eyesight or hearing are at play

– Extraneous: Fatigue, room temperature, distractions, etc. are at play

Measurement Scales

• In research we collect data. • These data can be classified into 4 categories.

– Nominal– Ordinal– Interval– Ratio

• The type of data we have dictates what statistics are used. More about that later…

Note: The word data is plural. Never write that “data is”, it is “data are”

What is Nominal Data?

• Categorical data where the order of the categories is arbitrary and has no true meaning other than classification– Social Security number– Drivers License number– Male or Female– Ethnicity– Political Party Affiliation– Colors of marbles

• The text identifies this as Categorical Data

Nominal Data

• The data we collect often has to be converted to numbers for statistical or tabulation purposes.

• So when we have nominal categorical data we often arbitrarily assign a numerical value for tabulation purposes such as– Male =1 and Female = 2– Democrats = 1, Republicans = 2 and Other = 3– Green = 1, Blue = 2, Red = 3

Time to Think

• See if you can come up with 5 examples of nominal data!

What is Ordinal Data?

• A scale that expresses data as rankings, rather than scores– A, B, C, D, F– Socio Economic Status– Professorial ranks

• The distance between the categories is not equal; the difference between a F and D is probably not the same as the difference between an A and a B.

• The text classifies ordinal data as categorical data.

Recording Ordinal Data

• After we collect data from a survey instrument, we then have to transfer the data to an Excel spreadsheet, Statistical Package for the Social Sciences (SPSS) or some other software program for tabulation purposes.

• The data have to be converted to numbers. So we might code:– Full Professor = 3– Associate Professor = 2– Assistant Professor = 1

Fudging

• Many researchers treat ordinal data as they would interval or ratio data.– That is they convert it to a numerical value with

meaning• For example they may assign an A a value of 4, a B a

value of 3, etc. and then calculate a GPA for use in statistical analyses.

– Basically they are taking ordered data and turning it into interval data (more about interval data in a couple of slides)

Time to Think

• See if you can come up with 5 examples of ordinal data!

What is Interval Data?

• Measurement scales expressed in equal number units, but not having a true zero point – IQ score (there is no such thing as zero intelligence)– Scores on the Meyers-Briggs Scale (there is no zero)– Temperature (there is a zero but it has meaning,

it does not represent “nothingness”)– Belt sizes

• The text calls this quantitative data• When we record this data, we use the actual

numbers

Time to Think

• See if you can come up with 2 examples of interval data!– Why only 2 examples?

• It is hard to find interval data

What is Ratio Data?• Measurement scales expressed in equal number

units, but having a true zero point– Test scores– Salary– Weight– Distance

• For all practical purposes Interval data and Ratio data are treated the same statistically

• The text calls this quantitative data• When we record this data, we use the actual

numbers

Time to Think

• See if you can come up with 5 examples of ratio data!

What is a Hypothesis?

• A testable statement of a predicted relationship or difference among selected variables.

Why Use Hypotheses in Research?

• Forces us to think more deeply• Forces us to read the related literature• Clarifies our thinking• Makes our research

more scientific

Three Types of Hypotheses

• Directional • Nondirectional• Null

Directional Hypothesis

• A Directional Hypothesis is preferred in research.– Basically is says if “A” happens then “B” will

happen.– “If one pushes down on the accelerator pedal, the

car will go faster.”

Nondirectional Hypothesis

• A nondirectional hypothesis can be used if you think something will happen but your are not very certain what will happen. – “If students are taught a unit on multiculturalism,

their attitude toward other cultures will change”

• You don’t know if the students will end up being more positive or less positive to other cultures as a result of the teaching unit.

Research Hypothesis

• Both nondirectional or directional hypotheses are often referred to as research hypotheses.

Null Hypothesis?

• A hypothesis that states that no differences or relationship exists among specified variables.

• Also called the statistical hypothesis.• This is only used for statistical purposes.• If a null hypothesis is found in a research study, it

nearly always follows the research hypothesis. • In the old days of research, researchers would nearly

always state the null hypothesis.• Today it is sort of assumed that one has tested the null

hypothesis.

Hypothesis Shorthand

• In some texts you will see various notations (I call it shorthand) that is sometimes associated with hypotheses.– Ha or H1 is the research hypothesis

– H0 or Ho is the null hypothesis

Characteristics of a Good Research Hypothesis

• Declarative sentence • Is brief and clearly stated • Identifies at least two variables (independent & dependent)• States an expected (predicted) relationship between at least

one variable and at least one other variable • States the nature of the relationship • States the direction of the relationship • Implies that the predicted relationship can be tested

empirically • Consistent with known facts, prior research, or theory

Bad Research Hypotheses• The more supportive of political authorities a child is,

the less likely the child will be to engage in political dissent as an adult– Not testable

• Age determines whether a person is tolerant of social protest– Nondirectional

• In comparing individuals, some people are more likely to donate money to political candidates than other people. – No relationship is identified

Better Research Hypotheses

• If a prisoner is taught an in-demand skill during incarceration, he or she will be less likely to commit burglary upon release when compared to a similar prisoner without such training

• If elderly adults are taught to use the Internet (and provided free access to the necessary equipment and software), their feelings of loneliness will decrease

A Good Research Hypothesis

• Students in AEE 578 who can distinguish between independent and dependent variables will score higher on worksheet 3 than students who cannot distinguish between independent and dependent variables.

Time to Think

• See if you can write a good research hypothesis