Variables It is very It is very

important in important in research to see research to see variables, define variables, define them, and control them, and control or measure them.or measure them.

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

A A variablevariable is is any entity that can any entity that can take on different values take 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 the values for different people or for the same person at different times. same person at different times.

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

Variables in Variables in researchresearch

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

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

Measurement can involve merely Measurement can involve merely categorization (e.g. sex, country, etc.)categorization (e.g. sex, country, 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 individuals variables that differ among individuals may not necessarily differ over time.may not necessarily differ over time.

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

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

OperationalizationOperationalization

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 be constructs, or traits that cannot be observed directly.observed directly.

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

OperationalizationOperationalization

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 or With students’ intelligence scores or TOEFL scores, we now have 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 of the variable.the variable.

Important point!Important point!

Operational definitions must be Operational definitions must be based upon a theory that is 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” we the construct of “proficiency” we should construct a test based on should construct a test based on an accepted theory or model of an accepted theory or model of language proficiency.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 able variables in research, we must be able to identify each variable. Variables can to identify each variable. Variables can be classified as: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 do An important distinction having to do with the term 'variable' is the 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 designs. is also used in other research designs.

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

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

Independent Independent VariablesVariables

The independent variable is the major The independent variable is the major variable which you hope to investigate. variable which you hope to investigate. It is the variable which is selected, It is the variable which is selected, manipulated, and measured (its effect) manipulated, and measured (its effect) by the researcher. Examples:by the 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 language The effect of social class on language use.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 study dependent variable in one study may be an independent variable may be an independent variable in another study.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 to you may select for study in order to investigate whether it modifies the investigate whether it modifies the relationship between the dependent relationship between the dependent and independent variables.and independent 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 each lies in how the researcher views each in the study. 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 variable, relationship to the dependent variable, whereas for moderator variables, the whereas for moderator variables, the concern is with their effect on that concern is with their effect on that relationship.relationship.

Control variablesControl variables It is virtually impossible to include It is virtually impossible to include

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

Control variablesControl variables Control variables, then, are those Control variables, then, are those

that the researcher has chosen to that the researcher has chosen to keep constant, neutralize, or keep constant, neutralize, or otherwise eliminate so that they will otherwise eliminate so that they will not have an effect on the study.not have an effect on the study.

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

Intervening Intervening variablesvariables

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

Independent

Variable(s)

Dependent

Variable(s)

Intervening

Variable(s)

Moderator

Variable(s)

Control

Variable(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 category.variables fall into each category.

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

Measurement ScalesMeasurement Scales

To measure different variables, we To measure different variables, we have four measurement scales:have four 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 or Nominal scale classifies persons or

objects into two or more objects into two or more categories. Members of a category categories. Members of a category have a common set of 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. artificial True vs. 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 to Artificial categories are those to which the researcher places the which the researcher places the members, such as learning style members, such as learning style (field independent(field independent versus field versus field dependent).dependent).

Ordinal ScaleOrdinal Scale

Ordinal variables allow us to Ordinal variables allow us to rank order the items we measure rank order the items we measure in terms of which has less and in terms of which has less and which has more of the quality which has more of the quality represented by the variable, but represented by the variable, but still they do not allow us to say still they do not allow us to say "how much more.“"how much 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 characteristic how they possess the characteristic of interest. Members are placed in of interest. Members are placed in terms of highest to lowest, or most terms of highest to lowest, or most to least. Students may be ranked by to 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 between compare the sizes of differences between them. them.

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

Interval scales normally have an arbitrary Interval scales normally have an arbitrary minimum and maximum point. A score of minimum and maximum point. A score of zero in a spelling test does not represent zero in a spelling test does not represent an absence of spelling knowledge, nor an absence of spelling knowledge, nor does a score of 20 represent perfect does a score of 20 represent perfect spelling knowledge. 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 absolute properties of interval variables, it has absolute zero point. Height, weight, speed, and zero point. Height, weight, speed, and distance are examples of ratio scales. 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. For added, subtracted, multiplied, and divided. For example, we can say that a person who runs a example, we can say that a person who runs a mile in 5 minutes is twice as fast as a person mile in 5 minutes is twice as fast as a person who runs the mile in 10 minutes. Because ratio who runs the mile in 10 minutes. Because ratio scales are often used in physical scales are often used in physical measurements (where absolute zero exists), measurements (where absolute zero exists), they are not often employed in educational they are not often employed in educational research and testing.research and testing.