How are Quasi-experiments different from correlational studies?
Technically, they are a type of correlational study Quasi-experiments usually select only a certain range of values of an independent variable, while a typical correlational study measures all available values of an independent variable. Quasi-experiments usually have more control than a typical correlational study (but less than an experiment) Types of Quasi-experiments Quasi-experiments with “subject variables” Between-subjects examples Gender differences High vs. low self-esteem Quasi-experiments with environmental variables: Time Series Designs Within-subjects Types: One-group pretest-posttest No control group Very low internal validity Avoid if at all possible Interrupted Time-Series No control group Multiple measures of the DV before and after the introduction of the IV Example: the effect of the personal computer on productivity Repeated-Treatment Design No control group Repeat the treatment (IV) multiple times Obtain pre-test and post-test measures each time Example: the effect
