Variables

1. Chapter Three Variables

2. What is a Variable? • A variable is a variation within a class of objects (e.g., weight). • Identified in the hypothesis or research question • Varies in quality or magnitude (i.e., has two or more levels) • Each level must be clearly defined • Must be identified as independent or dependent when examining differences • A constant is a characteristic with no variations within a class of objects (e.g., grade level of fifth graders). • Researchers choose certain variables to study since they are suspected to be related to a possible relationship or have a difference to be discovered.

3. Quantitative Variables • A quantitative variable exists in some degree along a continuum from less to more. We can assign numbers to different individuals or objects to indicate how much of the variable they possess • Examples: height, weight, grams of fiber. • Can be subdivided into smaller units

4. Categorical Variables • A categorical variable does not vary in degree, amount, or quantity, but are qualitatively different • Examples: occupation, ethnicity, gender. • There is no middle ground or in-between measurement

5. The independent variable is what the researcher studies to see its relationship or effects. Presumed or possible cause of difference (e.g., behavior change) Variable thought to influence the dependent variable. “Independent” of any other variable in study. Independent variables are controlled by the researcher - either manipulated or selected A manipulated variable is a changed condition the researcher creates and “controls” during a study, also known as experimental or treatment variable A selected variable is an independent variable that already exists Example: (3) level(s) of fiber intake Independent Variables

6. Dependent Variables • The variable of primary interest • Research question/hypothesis describes, explains, or predicts changes in it • The dependent variable is what is being influenced or affected by the independent variable • Presumed results • Quantitative outcome (or output) variable of interest. • Medical Nutrition Therapy outcomes may be medical, functional, psychosocial, or economic… may refer to quantity or quality • Define outcomes so they can be reproducibly and accurately measured. • Example: serum cholesterol levels • In non-experimental research, also called criterion variable, outcome variable

7. Relationship between Variables • Cannot specify independent variables without specifying dependent variables • Number of independent and dependent variables depends on the nature and complexity of the study • The number and type of variables dictates which statistical test will be used Independent Variable(s) (i.e., presumed or possible cause of difference) Dependent Variable(s) (i.e., presumed results; outcomes of interest) Affects

8. Confounding or extraneousvariables have an unpredictable impact upon the dependent variable because they were not controlled. Example: exercise ability Try to eliminate or reduce the effects of extraneous variables. Attempt to control by holding them constant Control variables have a potential influence on the dependent variable that are removed or controlled. Example: Level of saturated fat intake Other Types of Variables

9. Operationalizing Variables • All variables need an operationalization • Multiple operationalizations exist for most variables • It may be possible to include several measures, such as parent report of behavior, personality test, observations of a particular behavior in the classroom • Specifies the way in which variable is observed or measured • Practical and useful? • Justified argument? • Coincides with the conceptual definition? • Strive for definitions that permit replication

10. Chapter Three Hypotheses

11. Advantages Think about possible outcomes Make predictions based on prior evidence Determine if investigating a relationship. Disadvantages May lead to an unintentional bias May be inappropriate for certain types of research May miss other phenomenon by focusing on a hypothesis Hypothesis Definition: A prediction regarding possible outcomes of a study.

12. Types of Hypotheses • Null or Nondirectional • Does not make a prediction about direction of outcome. Representing an equality. • “There is no difference…” • “There is no association…” • Directional/Research • A specific direction (e.g., higher, lower, more, less) is indicated; it is a prediction of outcome; represents possible inequality. • Direction may be based on literature review, personal experience, or findings of others

13. “Well-Written” Hypothesis • Stated in declarative form (not as a question). • Posits an expected relationship between variables. • Reflect the theory or literature upon which they are based. • Brief and to the point. • Testable. • Tells what you are going to do, not how.

14. Example Null Hypothesis • Purpose of the study: To examine the effects that nutrition education on healthy eating knowledge, healthy eating attitudes, healthy eating behavior, healthy eating intentions, and physical activity attitudes. • H01: There is no difference between Nutrition Knowledge pretest and posttest scores. • H01a: Within students • H01b: Between schools • H01c: Between genders • H01d: Among age groups