Cofounding and Obscuring Variables - Chapter 11 (PSYCH 344)

One Group, Pretest/Posttest Design

An experiment in which a researcher results one group of participants; measures them on a pretest; exposes them to a treatment intervention, or charge; 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 Threats

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 it's own typical, or mean, level the next time it is measured (With or without the experimental treatment or intervention)

Regression Threat

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

(Leaving before the test could end)

Testing Threat

In a repeated-measures experimental 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

(Only one of the groups experience attrition)

Observer Bias

A bias that occurs when observer expectation influence the interpretation of participant behaviors or the outcome of the study

Demand Characteristic

A cue leads participants to guess a study's hypotheses or goals; a threat to internal validity

(Experimental Demand)

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 is 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

(Blind Design)

Placebo Effect

A response or effect that occurs when people receiving 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

(Null Result)

Ceiling Effect

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

Manipulation Check

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

Noise

Unsystematic variability among the members of the group in an experiment, which might be caused by the situation noise, individual differences, or measurement error

(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. Measurement errors 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 too high or too low

Situation Noise

Unrelated events or distraction in the external environment that create unsystematic variability within the 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; the probability of not making a Type II error

(Statistical Validity)