Defining and Measuring Variables

1. Defining and Measuring Variables PSYC 350 January 27, 2010

2. Outline: Defining and measuring variables Observations, constructs, and theories Inductive and deductive reasoning IVs and DVs Operational definitions Hypotheses

3. Steps in the research process Find a research idea Convert the idea into a hypothesis Define and measure variables Identify participants Select a research strategy Conduct the study Evaluate the data Report the results Refine/reformulate your research idea

8. Psychological science is characterized by the back-and-forth use of inductive and deductive reasoning. Inductive reasoning Particular ? general Infer constructs/theories from empirical observations Deductive reasoning General ? particular Use constructs/theories to make predictions regarding empirical observations

10. Independent and dependent variables Independent variable (IV) What the researcher wants to see the effect of Variable that is manipulated (circumstances) The IV is divided into levels or conditions (e.g., experimental and control conditions) Variable that is independent of the participant�s behavior Dependent variable (DV) What the researcher uses to measure the effect of the IV Variable that is measured (behavior) Variable that is dependent on the participant�s behavior

11. Independent and dependent variables

12. Operational definitions A construct cannot be directly measured or observed, but we can measure or observe external factors associated with the construct. E.g., alertness or vigilance could be operationally defined as being quick to respond to the appearance of a target.

13. Operational definitions Researchers translate a construct into a study-specific variable They specify the operations required to manipulate or measure the construct They provide enough detail so that other researchers can replicate the research

14. Operationally defining IVs and DVs Example: Television violence (IV) At least 75% of judges rate a TV show as violent Show has four of ten items from a violence checklist Levels of violence (Levels of the IV) Violent level: Shows that 75% of people rated as violent Non-violent level: Shows that 0% of people rated as violent Aggressive behavior (DV) Judges� rating of aggressive behavior (1-7) during one hour of free-play Percentage of time spent playing with toys classified as aggressive (e.g., toy guns, knives, tanks) versus non-aggressive (trucks, tools, dolls)

15. Hypotheses A hypothesis is an educated guess regarding the relationship between circumstances and behavior A hypothesis is a statement regarding the expected relationship between two variables A hypothesis can be expressed at both the construct level and the operational level

16. Hypotheses: Three dimensions Null or research Directional or nondirectional Conceptual (construct level) or operational

17. Hypotheses Null hypothesis A statement of equality Predicts no relationship between two variables The hypothesis to be proven false Research hypothesis A statement of inequality Predicts a relationship between two variables The hypothesis in search of support by evidence

20. Sample hypotheses Construct level Children exposed to violent television will display more aggressive play behavior than children exposed to non-violent television. Operational level Children who watch 5 hours of television programming that is rated as violent will spend more time during a one-hour free-play period playing with toys categorized as aggressive than children who watch 5 hours of television rated as nonviolent.

21. Is the hypothesis written at the construct or the operational level? 1. When asked to make a list of their friends, ten-year-olds who attend public school will list more friends than ten-year-olds who are home-schooled. 2. Children who attend public school will have more highly developed social skills than children who are home-schooled. 3. Practice improves memory performance. 4. Participants who read a list of words 3 times will recall more words than participants who read a list of words once.

23. Professor Sullivan wants to determine how students� study habits affect their performance on an exam. She divides her class in half by having them draw numbers out of a hat and then puts the groups in adjoining rooms. She tells the students in Room 1 to study their notes individually, without talking to one another. She tells the students in Room 2 to get into groups of four and discuss the topics with each other. After allowing both rooms of students one hour of study time, she administers the exam and records the scores.

24. Conclusions In psychological science, researchers move between the levels of observation and construct/theory. Inductive reasoning is used to formulate constructs and theories from observations. Deductive reasoning is used to formulate hypotheses from constructs and theories. A hypothesis is an educated guess regarding the relationship between circumstances and behavior. Independent variables and dependent variables specify the circumstances and behavior under investigation. Variables must be operationally defined (made observable/measurable) before a hypothesis can be tested.