Understanding Research Methods by Mildred L. Patten

Author:Mildred L. Patten
Language: eng
Format: epub
Tags: Research, Social Science, Methodology, Sociology
Publisher: Pyrczak Publishing

tion in the two groups, which could affect self-concept.

Selection can also interact with a threat called mortality (i.e., differential loss of participants from the groups to be compared). For example, those in an experimental school may have a higher dropout rate than those in a control school. If those who drop out have lower self-concepts, the posttest mean for the experimental group will be higher than the pretest mean, resulting in a statistical change in the average that is not the result of the treatment. At the same time, the control group will not have as

much of a change because it has a lower dropout rate.

All threats to internal validity can be overcome by using a true experimental design (see Topic 34), in which participants are assigned at random to experimental and control conditions. Because random assignment has no bias (or favorites), both groups are equally likely to experience the same environmental events (have the same history), mature at the same rates, drop out at the same rates, and so on.

Exercise on Topic 35

1. What is the name of the threat that says taking a pretest may affect performance on a posttest?

2. Suppose that an experimental group is being taught letters of the alphabet as a treatment. At about the same time, the students are watching an educational program on television, from which they learn the names of the letters. What is the name of the threat that this problem illustrates?

3. If observers are more tired and less astute when making posttest observations than when making pretest observations, what threat is operating? )n£h "' Heno

4. What is the name of the threat posed by nonrandom assignment of participants to experimental and control groups?

5. If infants naturally improve in visual acuity and thus perform better at the end of an experiment than at the beginning, what threat is operating?

6. Under what circumstance will statistical regression operate?

7. How can we overcome all the threats to internal validity?

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