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Variables and Variables and HypothesesHypotheses

Chapter ThreeChapter Three

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Variables and HypothesesVariables and HypothesesChapter ThreeChapter Three

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What is a Variable?What is a Variable?

A A variablevariable is a variation within a class of is a variation within a class of objects (i.e., eye color).objects (i.e., eye color).

A A constantconstant is a characteristic with no is a characteristic with no variations within a class of objects (i.e., grade variations within a class of objects (i.e., grade level of ninth graders).level of ninth graders).

Researchers choose certain variables to study Researchers choose certain variables to study since they are suspected to be related to a since they are suspected to be related to a possible relationship to be discovered.possible relationship to be discovered.

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Quantitative vs. Categorical VariablesQuantitative vs. Categorical Variables

Variables are classified as either Variables are classified as either quantitativequantitative or or categoricalcategorical

A quantitative variableA quantitative variable is conceptualized is conceptualized and analyzed in distinct categories, with and analyzed in distinct categories, with no continuum implied (i.e., height).no continuum implied (i.e., height). Can be subdivided into smaller unitsCan be subdivided into smaller units

A categorical variableA categorical variable does not vary in does not vary in degree, amount, or quantity, but are degree, amount, or quantity, but are qualitatively differentqualitatively different (i.e., political party). (i.e., political party). There is no middle ground or in-between There is no middle ground or in-between

measurementmeasurement

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Quantitative vs. Categorical Variables (Figure 3.1)Quantitative vs. Categorical Variables (Figure 3.1)

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Independent vs. Dependent VariablesIndependent vs. Dependent Variables

The The independent variableindependent variable is what the researcher is what the researcher studies to see its relationship or effects.studies to see its relationship or effects. Presumed or possible causePresumed or possible cause

The The dependent variabledependent variable is what is being is what is being influenced or affected by the influenced or affected by the independent independent variablevariable Presumed resultsPresumed results

Independent variables may be either Independent variables may be either manipulatedmanipulated or or selectedselected A A manipulated variablemanipulated variable is a changed condition the is a changed condition the

researcher creates during a study, also known as an researcher creates during a study, also known as an experimentalexperimental or or treatment variabletreatment variable

A A selected variableselected variable is an independent variable that is an independent variable that already existsalready exists

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The Relationship between The Relationship between Independent and Dependent Independent and Dependent

VariablesVariables

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Other Types of VariablesOther Types of Variables

Outcome VariableOutcome Variable A dependent variable that is quantitativeA dependent variable that is quantitative Most studies demonstrating this would have a Most studies demonstrating this would have a

categorical independent variablecategorical independent variable The investigator is interested in the effects that The investigator is interested in the effects that

might lead to differences in methods = might lead to differences in methods = outcomesoutcomes Moderator VariableModerator Variable

Special type of independent variableSpecial type of independent variable Selected to determine if it affects (modifies) the Selected to determine if it affects (modifies) the

basic relationship between the primary basic relationship between the primary independent variable and the dependent variable independent variable and the dependent variable (Figure 3.2)(Figure 3.2)

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Other Types of VariablesOther Types of Variables(cont.)(cont.)

Extraneous VariableExtraneous Variable Independent variables that have not been Independent variables that have not been

controlledcontrolled Considered a basic problem in researchConsidered a basic problem in research The task is to control these variables by The task is to control these variables by

reducing or eliminating their effectsreducing or eliminating their effects A method to control extraneous variables is to A method to control extraneous variables is to

hold them constanthold them constant Figure 3.3 illustrates the importance of Figure 3.3 illustrates the importance of

identifying extraneous variablesidentifying extraneous variables

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Examples of Extraneous Variables (Figure 3.3)Examples of Extraneous Variables (Figure 3.3)

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What is a Hypothesis?What is a Hypothesis? A A hypothesishypothesis is a prediction regarding the is a prediction regarding the

possible outcome of a studypossible outcome of a study Advantages of stating hypotheses include:Advantages of stating hypotheses include:

Forces us to think more deeply and specifically about the Forces us to think more deeply and specifically about the possible outcomes of the studypossible outcomes of the study

Enables us to make specific predictions based on prior Enables us to make specific predictions based on prior evidence or theoretical argumentevidence or theoretical argument

Helps to clarify whether we are or aren’t investigating a Helps to clarify whether we are or aren’t investigating a relationshiprelationship

Disadvantages of stating hypotheses include:Disadvantages of stating hypotheses include: May lead to a bias on the part of the researcherMay lead to a bias on the part of the researcher In some studies, it would be presumptuous to predict what In some studies, it would be presumptuous to predict what

findings would befindings would be Focusing on the hypothesis could prevent the researcher Focusing on the hypothesis could prevent the researcher

from seeing other phenomena that might be important to from seeing other phenomena that might be important to the studythe study

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Hypotheses from a Single Research Question Hypotheses from a Single Research Question (Figure 3.4)(Figure 3.4)

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Directional vs. Non-directional Directional vs. Non-directional HypothesesHypotheses

A A directional hypothesisdirectional hypothesis is one in which the researcher is one in which the researcher indicates the specific direction that he or she expects will indicates the specific direction that he or she expects will emerge in a relationship in the study. emerge in a relationship in the study. The direction is based on what the researcher has found from:The direction is based on what the researcher has found from:

LiteratureLiterature Personal experiencesPersonal experiences Experience from othersExperience from others

A non-directional hypothesis is when there is no specific A non-directional hypothesis is when there is no specific prediction about what direction the outcome of a study will prediction about what direction the outcome of a study will take.take. Sometimes it is difficult to make specific predictions upon a studySometimes it is difficult to make specific predictions upon a study

A study may state that it would point to non-specific directions vs. A study may state that it would point to non-specific directions vs. distinct possibilitiesdistinct possibilities

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Directional vs. Non-Directional Directional vs. Non-Directional Hypotheses (Figure 3.5)Hypotheses (Figure 3.5)