Variables And Measurement Scales

1. Variables
It is very important in It is very important in
research to see research to see
variables, define variables, define
them, and control or them, and control or
measure them.measure them.
Name some of the Name some of the
variables in a variables in a
classroom.classroom.

2. Outline of today’s Outline of today’s
presentationpresentation
1.The concept and definition of variable
2.Variables in research
3.Constructs versus variables
4.Operationalization
5.Types and functions of variables
6.Measurement Scales

3. The concept of variableThe concept of variable
The concept of variable is basic but very The concept of variable is basic but very
important in research. You won't be able important in research. You won't be able
to do very much in research unless you to do very 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 take on any entity that can take on
different values different values across individuals and time. across individuals and time.

4. Some examplesSome examples
AgeAge can be considered a variable because can be considered a variable because
age can take different values for different age can take different values for different
people or for the same person at different people or for the same person at different
times. times.
Similarly, Similarly, countrycountry can be considered a can be considered a
variable because a person's country can be variable because a person's country can be
assigned a value. assigned a value.

5. Variables in researchVariables in research
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 from The measurement may be different from
everyday notions of measurement such as everyday notions of measurement such as
weight and temperature. weight and temperature.
Measurement can involve merely Measurement can involve merely
categorization (e.g. sex, country, etc.)categorization (e.g. sex, country, etc.)

6. RememberRemember
Most variables that differ over time also vary Most variables that differ over time also vary
among individuals, but the reverse is not true. among individuals, but the reverse is not true.
That is, the variables that differ among That is, the variables that differ among
individuals may not necessarily differ over time.individuals may not necessarily differ over time.
An example for the former is “proficiency” and An example for the former is “proficiency” and
for the latter is “sex.”for the latter is “sex.”
Can you give some more examples for the two Can you give some more examples for the two
variables?variables?

7. OperationalizationOperationalization
Variables such as intelligence, motivation, Variables such as intelligence, motivation,
and academic achievement are concepts, and academic achievement are concepts,
constructs, or traits that cannot be observed constructs, or traits that cannot be observed
directly.directly.
They should be stated in precise definitions They should be stated in precise definitions
that can be observed and measured. This that can be observed and measured. This
process is called operationalization.process is called operationalization.

8. OperationalizationOperationalization
Intelligence
Trait or construct
Scores on the
Wechsler Adult
Intelligence
Scale
Operational definition of
intelligence
operationalization

9. OperationalizationOperationalization
Proficiency
Trait or construct
Scores on the
TOEFL test
Operational definition of
proficiency

10. Operational definition of a
variable
With students’ intelligence scores or TOEFL With students’ intelligence scores or TOEFL
scores, we now have observable and quantifiable scores, we now have observable and quantifiable
definitions of what the researcher means by the definitions of what the researcher means by the
constructs of “intelligence” and “proficiency”.constructs of “intelligence” and “proficiency”.
This is an This is an operational definitionoperational definition of the variable. of the variable.

11. Important point!Important point!
Operational definitions must be based Operational definitions must be based
upon a theory that is generally recognized upon a theory that is generally recognized
as valid.as valid.
For example, to operationalize the For example, to operationalize the
construct of “proficiency” we should construct of “proficiency” we should
construct a test based on an accepted construct a test based on an accepted
theory or model of language proficiency.theory or model of language proficiency.

12. Different types and Different types and
functions of variablesfunctions of variables
In addition to knowing how constructs are In addition to knowing how constructs are
operationalized as variables, operationalized as variables, it is important it is important
to understand how such variables are to understand how such variables are
classified and manipulated by researchers in classified and manipulated by researchers in
their quest to empirical knowledge.their quest to empirical knowledge.
To that end, we describe five different To that end, we describe five different
functions of variables.functions of variables.

13. Functions of variablesFunctions of variables
To assess the relationship between variables in To assess the relationship between variables in
research, we must be able to identify each research, we must be able to identify each
variable. Variables can be classified as:variable. Variables can be classified as:
1.1.IndependentIndependent
2.2.DependentDependent
3.3.ModeratorModerator
4.4.ControlControl
5.5.InterveningIntervening

14. Independent vs. Dependent Independent vs. Dependent
VariablesVariables
An important distinction having to do with the An important distinction having to do with the
term 'variable' is the distinction between an term 'variable' is the distinction between an
independentindependent and and dependentdependent variable. variable.
This distinction is particularly relevant when you This distinction is particularly relevant when you
are investigating cause-effect relationships are investigating cause-effect relationships
(experiment). However, the concept is also used (experiment). However, the concept is also used
in other research designs. in other research designs.

15. Independent vs. dependent V.Independent vs. dependent V.
In fact In fact the independent variable is the independent variable is
what you (or nature) manipulateswhat you (or nature) manipulates -- --
a treatment or program or cause. a treatment or program or cause. The The
dependent variable is what is dependent variable is what is
affected by the independent variableaffected by the independent variable
-- your effects or outcomes. -- your effects or outcomes.

16. Independent VariablesIndependent Variables
The independent variable is the major variable The independent variable is the major variable
which you hope to investigate. It is the variable which you hope to investigate. It is the variable
which is selected, manipulated, and measured which is selected, manipulated, and measured
(its effect) by the researcher. Examples:(its effect) by the researcher. Examples:
The effect of your instruction on reading scores The effect of your instruction on reading scores
of your students.of your students.
The effect of social class on language use.The effect of social class on language use.

17. Dependent variableDependent variable
The dependent variable is the variable The dependent variable is the variable
which you observe and measure to which you observe and measure to
determine the effect of the independent determine the effect of the independent
variable.variable.
In the previous examples, the reading In the previous examples, the reading
scores of your students and the use of scores of your students and the use of
language would be the dependent variable.language would be the dependent variable.

18. Two pointsTwo points
•A variable that functions as a dependent A variable that functions as a dependent
variable in one study may be an variable in one study may be an
independent variable in another study.independent variable in another study.
•Depending on the design of the study, we Depending on the design of the study, we
may have more than one independent and may have more than one independent and
even more than one dependent variable in even more than one dependent variable in
the study.the study.

19. Moderator variableModerator variable
A moderator variable is a special type of A moderator variable is a special type of
independent variable which you may select for independent variable which you may select for
study in order to investigate whether it study in order to investigate whether it
modifies the relationship between the modifies the relationship between the
dependent and independent variables.dependent and independent variables.
Example, sex in the study of the effect of Example, sex in the study of the effect of
instruction on students’ reading scoresinstruction on students’ reading scores

20. Independent vs. moderator Independent vs. moderator
variablevariable
The essential difference between independent The essential difference between independent
and moderator variables lies in how the and moderator variables lies in how the
researcher views each in the study. researcher views each in the study.
For independent variables, the concern is with For independent variables, the concern is with
their direct relationship to the dependent their direct relationship to the dependent
variable, whereas for moderator variables, the variable, whereas for moderator variables, the
concern is with their effect on that relationship.concern is with their effect on that relationship.

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

22. Control variablesControl variables
Control variables, then, are those that the Control variables, then, are those that the
researcher has chosen to keep constant, researcher has chosen to keep constant,
neutralize, or otherwise eliminate so that neutralize, or otherwise eliminate so that
they will not have an effect on the study.they will not have an effect on the study.
Example, the effect of outside practice on Example, the effect of outside practice on
reading in the previous example.reading in the previous example.

23. Intervening variablesIntervening variables
Intervening variables are constructs (other Intervening variables are constructs (other
than the construct under study) that may than the construct under study) that may
explain the relationship between explain the relationship between
independent and dependent variables but are independent and dependent variables but are
not directly observable themselves.not directly observable themselves.
We are somehow aware of their effects, but We are somehow aware of their effects, but
we are not able to account for them.we are not able to account for them.

24. The relationship among variablesThe relationship among variables
Independent
Variable(s)
Dependent
Variable(s)
Intervening
Variable(s)
Moderator
Variable(s)
Control
Variable(s)
The Study

25. Two pointsTwo points
When designing a study, the researcher When designing a study, the researcher
determines which variables fall into each determines which variables fall into each
category.category.
In real situations, all five types of In real situations, all five types of
variables may not be included in all variables may not be included in all
studies.studies.

26. Measurement ScalesMeasurement Scales
To measure different variables, we have four To measure different variables, we have four
measurement scales:measurement scales:
3.3.Nominal ScaleNominal Scale
4.4.Ordinal ScaleOrdinal Scale
5.5.Interval ScaleInterval Scale
6.6.Ratio ScaleRatio Scale

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

28. True vs. artificial categoriesTrue vs. artificial categories
True categories are those to which the True categories are those to which the
member naturally falls, such as gender (male member naturally falls, such as gender (male
vs. female).vs. female).
Artificial categories are those to which the Artificial categories are those to which the
researcher places the members, such as researcher places the members, such as
learning style (field independentlearning style (field independent versus field versus field
dependent).dependent).

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

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

31. Interval ScaleInterval Scale
Not only rank order the items that are measured, Not only rank order the items that are measured,
but also to quantify and compare the sizes of but also to quantify and compare the sizes of
differences between them. differences between them.
For example: students performance on a spelling test For example: students performance on a spelling test
A score of 16 will be higher than 14 and lower A score of 16 will be higher than 14 and lower
than 18 and the difference between them is 2 than 18 and the difference between them is 2
points (equal intervals). points (equal intervals).
Interval scales normally have an arbitrary minimum Interval scales normally have an arbitrary minimum
and maximum point. A score of zero in a spelling and maximum point. A score of zero in a spelling
test does not represent an absence of spelling test does not represent an absence of spelling
knowledge, nor does a score of 20 represent knowledge, nor does a score of 20 represent
perfect spelling knowledge. perfect spelling knowledge.

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