1. Chapter 5:
Variables and measurement IN research

2. Dependent Variables
Dependent/response variable: a variable that is measured or observed from an individual.
Reliability: the degree to which the results of a study can be replicated under similar conditions.
Operational definition: the definition of an abstract concept used by a researcher to measure or manipulate the concept in a research study
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

3. happy sad anxious excited
Scales of Measurement
Nominal: non-ordered category responses
Example:
How do you feel today? (Circle one)
happy sad anxious excited
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

4. Scales of Measurement Ordinal: ordered category responses Example:
How do you feel today? (Circle one)
very sad sad neutral happy very happy
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

5. Scales of Measurement
Interval: equally spaced, numerical responses, values are not ratio relations
Example:
Rate how happy you are today: 1 ‑ 5,
1 = least happy, 5 = most happy
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

6. Scales of Measurement
Ratio: equally spaced, numerical responses, values are ratio relations
Examples:
Time
Height
Accuracy
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

7. Scales of Measurement
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

8. Validity and Response Scales
Construct validity: indicates that a survey measures the behavior it is designed to measure.
Nonverbal scale: survey response scale that involves pictorial response categories for participants with low verbal skills (e.g., children).
Face validity: on the surface, a study or scale appears to be intuitively valid.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

9. Reliability of Measurements and Response Scales
Inter-observer/Inter-rater reliability: a measure of the degree to which different observers observe or code behaviors in similar ways.
For example, in a study using naturalistic observations, there are typically multiple observers of the behaviors of interest, either observing at the same time to ensure that all behaviors are recorded or observing at different times to allow the participants to be observed for longer periods of time.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

10. Independent Variables
Independent variable: a variable in an experiment that is manipulated by the researcher such that the levels of the variable change across or within subjects in the experiment.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

11. Independent Variables
Types of manipulations
As the presence and absence of a treatment or situation
As a type of treatment or situation
As the amount of a factor in a treatment or situation
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

12. Quasi-Independent Variables
Quasi-independent/subject variable: variable that allows comparison of groups of participants without manipulation (i.e., no random assignment).
Some examples of common quasi-independent variables used in psychological research include gender, age, personality types (e.g., introverts and extroverts), and ethnicity.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

13. Validity and Sources of Bias
Group differences
Order effects
Testing effects
Regression toward the mean
Hawthorne effect
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

14. Internal Validity
Internal validity: the degree to which a study provides causal information about behavior.
Confounding variable: an extraneous factor present in a study that may affect the results.
Experimenter bias: a source of bias in a study created when a researcher treats groups differently (often unknowingly) based on knowledge of the hypothesis.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

15. Internal Validity
Single-blind design: procedure used to hide the group assignment from the participants in a study to prevent their beliefs about the effectiveness of a treatment from affecting the results.
Placebo: a sugar pill given to the control group in a drug study to allow all groups to believe that they are receiving a treatment.
Double-blind design: procedure used to control for experimenter bias by keeping the knowledge of the group assignments from both the participants and the researchers who interact with the participants.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

16. Internal Validity
Testing effects: occur when participants are tested more than once in a study with early testing affecting later testing.
Within-subjects variable: each participant experiences all levels of the variable.
Between-subjects variable: each participant experiences only one level of the independent variable.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

17. Internal Validity
Counterbalance: a control used in within-subjects experiments where different participants are assigned in equal numbers to the different orders of the conditions
Regression Toward the Mean: can occur when participants score higher or lower than their personal average—the next time they are tested, they are more likely to score near their personal average, making overall scores unreliable
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

18. External Validity
External validity: the degree to which the results of a study apply to individuals and realistic behaviors outside the study.
Hawthorne effect: a source of bias that can occur in a study due to participants changing their behavior because they are aware that they are being observed.
Field experiment: an experiment conducted in the participants’ natural environment.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

19. Sources of Bias Specific to a Field of Study
As a researcher becomes more familiar with an area of psychological study, these sources of bias become clearer, and ways to control for these biases can be built into the design of the studies.
For example, in some memory research where study- test time delay is not an independent variable of interest. Instead, it can become a source of bias if different individuals are tested after different delays and delay is not a variable of interest in the study.
McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.