Quiz #5

1. (4 points) List and briefly describe two methodological problems which may lead to difficulties in comparing groups to one another.

1. Lack of a representative sampling. (eg. Self selected biases)
2. Extraneous variables may be confounded with group membership, so mean differences between groups may be due to the extraneous variable.
3. Lack of reliability/validity of measures in one or more groups.
4. Investigator bias.

2. (3 points) Name three different levels at which groups may be compared to one another in the study of individual differences.

1. Mean differences
2. Variance differences.
3. Differences in correlations or trait relationships between variables.
4. Different causal factors in various groups. (eg. Compare heritibilities between groups)

3. (3 points) Briefly define "effect size" in the study of group differences, and indicate approximate levels of small, medium, and large effects.

Mean difference between groups, expressed in standard deviation units.

Small d=.2

Medium d=.5

Large d=.8