Exam 8: Experimental Designs

Experimenters using quasi-experimental designs rule out threats to internal validity by doing all but which one of the following?

A pretest is an essential feature of true experimental designs.

Testing is likely to threaten internal validity in a

In a within-subjects design,

Random assignment of subjects to experimental conditions eliminates the possibility of _________ and __________ as threats to internal validity.

The Clore et al. study of the effect of interracial contact at a summer camp on interracial attitudes

Consider the following experiment on helping disabled persons. One Monday, in a campus area with park benches where students often meet, an investigator placed one of two confederates: either a handicapped woman in a wheelchair or a nondisabled woman. The disabled woman was there between the hours of 9:00 a.m. and 12:00 noon, and the nondisabled woman was there between the hours of 1:00 and 4:00 p.m. While in the setting, every fifteen minutes each woman asked a randomly chosen passerby to help her find a lost earring. An observer, appearing to be reading a book while seated on a nearby bench, recorded the amount of time each subject spent helping to find the earring. If the subject had not left in fifteen minutes, the confederate pretended to find the earring. a. What is the independent variable in this study? b. What variable is confounded with the manipulation of the independent variable? (Identify a specific variable, not a class of extraneous variables such as history, maturation, etc.)

Suppose you want to study the effects of study abroad on students' attitudes toward immigration. You contact the Study Abroad Office and identify all students selected for study broad. You measure the attitudes of members of this group before they go abroad and then measure their attitudes again after they return home. If you found more tolerance after they return home, this could be due to the study abroad experience or to other factors. Which of the following threats to validity is not an alternative interpretation?

__________ is due to random measurement error among extreme scorers, whereas __________ may be due to systematic measurement error among human observers.

In a study of interpersonal attraction, subjects watched a videotape featuring a person who was (1) either competent or incompetent, and (2) either did or did not spill coffee on himself (i.e., "blundered"). After watching the tape, all subjects indicated how much they liked the person in the film on a seven-point scale. Consider the following outcome: This outcome shows

The interaction of the independent variable (or treatment) with some other variable (e.g., a variable represented by history or maturation) poses a threat to the external validity of true experiments. What are some solutions to problems of (a) sample selection-X interaction, (b) maturation-X interaction, and (c) history-X interaction? (Recall that X is an independent variable.)