Variables It is very It is very important in important in research to see research to see variables, variables, define them, and define them, and control or control or measure them.measure them.

Name some of the Name some of the variables in a variables in a classroom.classroom.

Outline of today’s Outline of today’s presentationpresentation

1. The concept and definition of variable

2. Variables in research3. Constructs versus variables4. Operationalization5. Types and functions of variables6. Measurement Scales

The concept of The concept of variablevariable

The concept of variable is The concept of variable is basic but very important in basic but very important in research. You won't be able to research. You won't be able to do very much in research do very much in research unless you know how to deal unless you know how to deal with variables. with variables.

A A variablevariable is is any entity that can take any entity that can take on different values on different values across across individuals and time. individuals and time.

Some examplesSome examples AgeAge can be considered a variable can be considered a variable because age can take different because age can take different values for different people or for values for different people or for the same person at different times. the same person at different times.

Similarly, Similarly, countrycountry can be considered can be considered a variable because a person's a variable because a person's country can be assigned a value. country can be assigned a value.

Variables in Variables in researchresearch

Variables are things that we Variables are things that we measure, control, or manipulate in measure, control, or manipulate in research. research.

The measurement may be different The measurement may be different from everyday notions of measurement from everyday notions of measurement such as weight and temperature. such as weight and temperature.

Measurement can involve merely Measurement can involve merely categorization (e.g. sex, country, categorization (e.g. sex, country, etc.)etc.)

RememberRemember Most variables that differ over time Most variables that differ over time also vary among individuals, but the also vary among individuals, but the reverse is not true. That is, the reverse is not true. That is, the variables that differ among variables that differ among individuals may not necessarily individuals may not necessarily differ over time.differ over time.

An example for the former is An example for the former is “proficiency” and for the latter is “proficiency” and for the latter is “sex.”“sex.”

Can you give some more examples for Can you give some more examples for the two variables?the two variables?

OperationalizatioOperationalizationn

Variables such as intelligence, Variables such as intelligence, motivation, and academic motivation, and academic achievement are concepts, achievement are concepts, constructs, or traits that cannot constructs, or traits that cannot be observed directly.be observed directly.

They should be stated in precise They should be stated in precise definitions that can be observed definitions that can be observed and measured. This process is and measured. This process is called operationalization.called operationalization.

OperationalizatioOperationalizationn

Intelligence

Trait or construct

Scores on the Wechsler Adult Intelligence Scale

Operational definition of intelligence

operationalization

OperationalizationOperationalization

Proficiency

Trait or construct

Scores on the TOEFL test

Operational definition of proficiency

Operational definition of a variable

With students’ intelligence scores With students’ intelligence scores or TOEFL scores, we now have or TOEFL scores, we now have observable and quantifiable observable and quantifiable definitions of what the researcher definitions of what the researcher means by the constructs of means by the constructs of “intelligence” and “proficiency”.“intelligence” and “proficiency”.

This is an This is an operational definitionoperational definition of the variable.of the variable.

Important point!Important point! Operational definitions must Operational definitions must be based upon a theory that is be based upon a theory that is generally recognized as valid.generally recognized as valid.

For example, to operationalize For example, to operationalize the construct of “proficiency” the construct of “proficiency” we should construct a test we should construct a test based on an accepted theory or based on an accepted theory or model of language proficiency.model of language proficiency.

Different types and Different types and functions of functions of variablesvariables

In addition to knowing how In addition to knowing how constructs are operationalized as constructs are operationalized as variables, variables, it is important to it is important to understand how such variables are understand how such variables are classified and manipulated by classified and manipulated by researchers in their quest to researchers in their quest to empirical knowledge.empirical knowledge.

To that end, we describe five To that end, we describe five different functions of variables.different functions of variables.

Functions of Functions of variablesvariables

To assess the relationship between To assess the relationship between variables in research, we must be variables in research, we must be able to identify each variable. able to identify each variable. Variables can be classified as:Variables can be classified as:

1.1.IndependentIndependent2.2.DependentDependent3.3.ModeratorModerator4.4.ControlControl5.5.InterveningIntervening

Independent vs. Independent vs. Dependent VariablesDependent Variables

An important distinction having to An important distinction having to do with the term 'variable' is the do with the term 'variable' is the distinction between an distinction between an independentindependent and and dependentdependent variable. variable.

This distinction is particularly This distinction is particularly relevant when you are investigating relevant when you are investigating cause-effect relationships cause-effect relationships (experiment). However, the concept (experiment). However, the concept is also used in other research is also used in other research designs. designs.

Independent vs. Independent vs. dependent V.dependent V.

In fact In fact the independent the independent variable is what you (or nature) variable is what you (or nature) manipulatesmanipulates -- a treatment -- a treatment or program or cause. or program or cause. The The dependent variable is what is dependent variable is what is affected by the independent affected by the independent variablevariable -- your effects or -- your effects or outcomes. outcomes.

Independent VariablesIndependent Variables The independent variable is the major The independent variable is the major variable which you hope to variable which you hope to investigate. It is the variable which investigate. It is the variable which is selected, manipulated, and is selected, manipulated, and measured (its effect) by the measured (its effect) by the researcher. Examples:researcher. Examples:

The effect of your instruction on The effect of your instruction on reading scores of your students.reading scores of your students.

The effect of social class on The effect of social class on language use.language use.

Dependent variableDependent variable

The dependent variable is the The dependent variable is the variable which you observe and variable which you observe and measure to determine the effect measure to determine the effect of the independent variable.of the independent variable.

In the previous examples, the In the previous examples, the reading scores of your students reading scores of your students and the use of language would and the use of language would be the dependent variable.be the dependent variable.

Two pointsTwo points1.1. A variable that functions as a A variable that functions as a

dependent variable in one dependent variable in one study may be an independent study may be an independent variable in another study.variable in another study.

2.2. Depending on the design of the Depending on the design of the study, we may have more than study, we may have more than one independent and even more one independent and even more than one dependent variable in than one dependent variable in the study.the study.

Moderator Moderator variablevariable

A moderator variable is a special A moderator variable is a special type of independent variable which type of independent variable which you may select for study in order you may select for study in order to investigate whether it modifies to investigate whether it modifies the relationship between the the relationship between the dependent and independent dependent and independent variables.variables.

Example, sex in the study of the Example, sex in the study of the effect of instruction on students’ effect of instruction on students’ reading scoresreading scores

Independent vs. Independent vs. moderator variablemoderator variable

The essential difference between The essential difference between independent and moderator variables independent and moderator variables lies in how the researcher views lies in how the researcher views each in the study. each in the study.

For independent variables, the For independent variables, the concern is with their direct concern is with their direct relationship to the dependent relationship to the dependent variable, whereas for moderator variable, whereas for moderator variables, the concern is with variables, the concern is with their effect on that relationship.their effect on that relationship.

Control variablesControl variables It is virtually impossible to It is virtually impossible to include all the potential variables include all the potential variables in each study. As a result, the in each study. As a result, the researcher must attempt to control, researcher must attempt to control, or neutralize, all other extraneous or neutralize, all other extraneous variables that are likely to have variables that are likely to have an effect on the relationship an effect on the relationship between the independent, dependent, between the independent, dependent, and moderator variables.and moderator variables.

Control variablesControl variables Control variables, then, are Control variables, then, are those that the researcher has those that the researcher has chosen to keep constant, chosen to keep constant, neutralize, or otherwise neutralize, or otherwise eliminate so that they will not eliminate so that they will not have an effect on the study.have an effect on the study.

Example, the effect of outside Example, the effect of outside practice on reading in the practice on reading in the previous example.previous example.

Intervening Intervening variablesvariables

Intervening variables are Intervening variables are constructs (other than the constructs (other than the construct under study) that may construct under study) that may explain the relationship between explain the relationship between independent and dependent independent and dependent variables but are not directly variables but are not directly observable themselves.observable themselves.

We are somehow aware of their We are somehow aware of their effects, but we are not able to effects, but we are not able to account for them.account for them.

The relationship among The relationship among variablesvariables

IndependentVariable(s)

DependentVariable(s)

InterveningVariable(s)

ModeratorVariable(s)

ControlVariable(s)

The Study

Two pointsTwo points When designing a study, the When designing a study, the researcher determines which researcher determines which variables fall into each variables fall into each category.category.

In real situations, all five In real situations, all five types of variables may not be types of variables may not be included in all studies.included in all studies.

Measurement ScalesMeasurement Scales To measure different To measure different

variables, we have four variables, we have four measurement scales:measurement scales:

1.1. Nominal ScaleNominal Scale2.2. Ordinal ScaleOrdinal Scale3.3. Interval ScaleInterval Scale4.4. Ratio ScaleRatio Scale

Nominal ScaleNominal Scale Nominal scale classifies persons Nominal scale classifies persons

or objects into two or more or objects into two or more categories. Members of a categories. Members of a category have a common set of category have a common set of characteristics, and each member characteristics, and each member may only belong to one category. may only belong to one category. Other names: categorical, Other names: categorical, discontinuous, dichotomous (only discontinuous, dichotomous (only two categories). two categories).

True vs. True vs. artificial artificial categoriescategories

True categories are those to True categories are those to which the member naturally falls, which the member naturally falls, such as gender (male vs. female).such as gender (male vs. female).

Artificial categories are those Artificial categories are those to which the researcher places to which the researcher places the members, such as learning the members, such as learning style (field independentstyle (field independent versus versus field dependent).field dependent).

Ordinal ScaleOrdinal ScaleOrdinal variables allow us to Ordinal variables allow us to rank order the items we rank order the items we measure in terms of which has measure in terms of which has less and which has more of the less and which has more of the quality represented by the quality represented by the variable, but still they do variable, but still they do not allow us to say "how much not allow us to say "how much more.“more.“

Example: Ranking studentsExample: Ranking students

Ordinal Ordinal ScaleScale

Ordinal scales both Ordinal scales both classifyclassify subjects and subjects and rankrank them in terms of them in terms of how they possess the how they possess the characteristic of interest. characteristic of interest. Members are placed in terms of Members are placed in terms of highest to lowest, or most to highest to lowest, or most to least. Students may be ranked by least. Students may be ranked by height, weight, or IQ scores. height, weight, or IQ scores. Ordinal scales do not, however, Ordinal scales do not, however, state how much difference there is state how much difference there is between the ranks. between the ranks.

Interval Interval ScaleScale

Not only rank order the items that are Not only rank order the items that are measured, but also to quantify and measured, but also to quantify and compare the sizes of differences compare the sizes of differences between them. between them.

For example: students performance on a For example: students performance on a spelling test A score of 16 will be spelling test A score of 16 will be higher than 14 and lower than 18 and higher than 14 and lower than 18 and the difference between them is 2 points the difference between them is 2 points (equal intervals). (equal intervals).

Interval scales normally have an Interval scales normally have an arbitrary minimum and maximum point. A arbitrary minimum and maximum point. A score of zero in a spelling test does score of zero in a spelling test does not represent an absence of spelling not represent an absence of spelling knowledge, nor does a score of 20 knowledge, nor does a score of 20 represent perfect spelling knowledge. represent perfect spelling knowledge.

Ratio Ratio ScaleScale

VVery similar to interval scale; has all the ery similar to interval scale; has all the properties of interval variables, it has properties of interval variables, it has absolute zero point. Height, weight, speed, absolute zero point. Height, weight, speed, and distance are examples of ratio scales. and distance are examples of ratio scales. Measurements made with ratio scales can be Measurements made with ratio scales can be added, subtracted, multiplied, and divided. added, subtracted, multiplied, and divided. For example, we can say that a person who For example, we can say that a person who runs a mile in 5 minutes is twice as fast as runs a mile in 5 minutes is twice as fast as a person who runs the mile in 10 minutes. a person who runs the mile in 10 minutes. Because ratio scales are often used in Because ratio scales are often used in physical measurements (where absolute zero physical measurements (where absolute zero exists), they are not often employed in exists), they are not often employed in educational research and testing.educational research and testing.