PSYC207 exam 3

Social norm

widely held beliefs about what most people in a group believe or value

Experiment

a study in which at least one variable is manipulated and another is measured

Manipulated variable

a variable in an experiment that a researcher controls, such as by assigning participants to its different levels (values)

Measured variable

a variable in a study whose levels (values) are observed and recorded

Independent variable

in an experiment, a variable that is manipulated; in a multiple-regression analysis, a predictor variable used to explain variance in the criterion variable

Condition

one of the levels of the independent variable in an experiment

Dependent variable

in an experiment, the variable that is measured. In a multiple-regression analysis, the single outcome, or criterion variable the researchers are most interested in understanding or predicting. Also called outcome variable

Control variable

in an experiment, any variable that an experimenter holds constant on purpose

• Not really variables at all; they do not vary

• Levels kept the same for all participants

• Eliminate alternative explanations → internal validity

Comparison group

a group in an experiment whose levels on the independent variable differ from those of the treatment group in some intended and meaningful way. Doesn’t need to be a control group

Control group / control condition

a level of an independent variable that is intended to represent “no treatment” or a neutral condition

Treatment group

the participants in an experiment who are exposed to the level of the independent variable that involves a medication, therapy, or intervention

Placebo group

a control group in an experiment that is exposed to an inert treatment, eg. a sugar pill

Confound

a general term for a potential alternative explanation for a research finding; a threat to internal validity

Design confound

a threat to internal validity in an experiment in which a second variable happens to vary systematically along with the independent variables and therefore is an alternative explanation for the results

Systematic variability

in an experiment, a description of when the levels of a variable coincide in some predictable way with experimental group membership, creating a potential confound

Unsystematic variability

in an experiment, a description of when the levels of a variable fluctuate independently of experimental group membership, contributing to variability within groups

Selection effect

a threat to internal validity that occurs in an independent-groups design when the kinds of participants at one level of the independent variable are systematically different from those at the other level

Matched groups

an experimental design technique in which participants who are similar on some measured variable are grouped into sets; the members of each matched set are then randomly assigned to different experimental conditions

Independent-groups design

an experimental design in which different groups of participants are exposed to different levels of the independent variable, such that each participant experiences only one level of the independent variable

Within-groups design

an experimental design in which each participant is presented with all levels of the independent variable

Posttest-only design

an experiment using an independent-groups design in which participants are tested on the dependent variable only once

Pretest/posttest design

an experiment using an independent-groups design in which participants are tested on the key dependent variable twice

Repeated-measures design

an experiment using a within-groups design in which participants respond to a dependent variable more than once, after exposure to each level of the independent variable

Concurrent-measures design

an experiment using a within-groups design in which participants are exposed to all the levels of an independent variable at roughly the same time, and a single attitudinal or behavioral preference is the dependent variable

Order effect

in a within-groups design, a threat to internal validity in which exposure to one condition changes participant responses to a later condition

Practice effect (fatigue effect)

a type of order effect in which participants’ performance improves over time because they become practiced at the dependent measure (not because of the manipulation or treatment)

Carryover effect

a type of order effect in which some form of contamination carries over from one condition to the next

Counterbalancing

in a repeated-measures experiment, presenting the levels of the independent variable to participants in different sequences to control for order effects

Full counterbalancing

a method of counterbalancing in which all possible condition orders are represented

Partial counterbalancing

a method of counterbalancing in which some, but not all, of the possible condition orders are represented

Latin square

a formal system of partial counterbalancing to ensure that every condition in a within-groups design appears in each position at least once

Manipulation check

in an experiment, an extra dependent variable researchers can include to determine how well a manipulation worked

Pilot study

a study completed before (or sometimes after) the study of primary interest, usually to test the effectiveness or characteristics of the manipulations

One-group, pretest/posttest design

an experiment in which a researcher recruits one group of participants; measures them on a pretest; exposes them to a treatment, intervention, or change; and then measures them on a posttest

Maturation threat

a threat to internal validity that occurs when an observed change in an experimental group could have emerged more or less spontaneously over time

History threat

a threat to internal validity that occurs when it is unclear whether a change in the treatment group is caused by the treatment itself or by an external or historical factor that affects most members of the group

Regression threat

a threat to internal validity related to regression to the mean, a phenomenon in which any extreme finding is likely to be closer to its own typical, or mean, level the next time it is measured (with or without the experimental treatment or intervention)

Regression to the mean

a phenomenon in which an extreme finding is likely to be closer to its own typical, or mean, level the next time it is measured, because the same combination of chance factors that made the finding extreme are not present the second time

Attrition threat

in a pretest/posttest, repeated-measures, or quasi-experimental study, a threat to internal validity that occurs when a systematic type of participant drops out of the study before it ends

Testing threat

in a repeated-measures experiment or quasi-experiment, a kind of order effect in which scores change over time just because participants have taken the test more than once; includes practice effects

Instrumentation threat

a threat to internal validity that occurs when a measuring instrument changes over time

Selection-history threat

a threat to internal validity in which a historical or seasonal event systematically affects only the participants in the treatment group or only those in the comparison group, not both

Selection-attrition threat

a threat to internal validity in which participants are likely to drop out of either the treatment group or the comparison group, not both

Observer bias

a bias that occurs when observer expectations influence the interpretation of participant behaviors or the outcome of the study

Demand characteristics

a cue that leads participants to guess a study’s hypotheses or goals; a threat to internal validity

Double-blind study

a study in which neither the participants nor the researchers who evaluate them know who is in the treatment group and who isi in the comparison group

Masked design

a study design in which the observers are unaware of the experimental conditions to which participants have been assigned

Placebo effect

a response or effect that occurs when people receiving an experimental treatment experience a change only because they believe they are receiving a valid treatment

Double-blind placebo control study

a study that uses a treatment group and a placebo group and in which neither the researchers nor the participants know who is in which group

Null effect

a finding that an independent variable did not make a difference in the dependent variable; there is no significant covariance between the two

Ceiling effect

an experimental design problem in which independent variable groups score almost the same on a dependent variable, such that all scores fall at the high end of their possible distribution

Floor effect

an experimental design problem in which independent variable groups score almost the same on a dependent variable, such that all scores fall at the low end of their possible distribution

Noise

unsystematic variability among the members of a group in an experiment, which might be caused by situation noise, individual differences, or measurement error (aka error variance, unsystematic variance)

Measurement error

the degree to which the recorded measure for a participant on some variable differs from the true value of the variable for that participant. May be random, such that scores that are too high and too low cancel each other out; or they may be systematic, such that most scores are biased either too high or too low

Situation noise

unrelated events or distractions in the external environment that create unsystematic variability within groups in an experiment

Power

the likelihood that a study will show a statistically significant result when an independent variable truly has an effect in the population

Interaction effect

a result from a factorial design, in which the difference in the levels of one independent variable changes, depending on the level of the other independent variable; a difference in differences

Factorial design

a study in which there are 2 or more independent variables, or factors

Cell

a condition in an experiment; in a simple experiment, it can represent the level of one independent variable; in a factorial design, it represents one of the possible combinations of two independent variables

Participant variable

a variable such as age, gender, or ethnicity whose levels are selected (ie, measured), not manipulated

Main effect

in a factorial design, the overall effect of one independent variable on the dependent variable, averaging over the levels of the other independent variable

Marginal means

in a factorial design, the arithmetic means for each level of an independent variable, averaging over the levels of another independent variable

Causal claims

• Making a claim about treatment, etc.

• Can only be tested with experiments

• Three rules:

  • (1) Covariance

  • (2) Temporal Precedence

  • (3) Internal Validity (ruling out alternative explanations)

Temporal precedence

can be established by an experiment, but not a correlational study; establishes that the independent variable came before the dependent variable; a component of causality