HOW SUBJECTS AND SAMPLING AFFECT RESEARCH
In reading and interpreting research you will need to be conscious of how the sampling procedures might have affected the results and how the characteristics of the subjects affect the usefulness and the ability of the results.
Knowledge of Sampling Procedures
To understand how sampling may affect research it is essential to know the characteristics of different sampling procedures. This knowledge will help you interpret the sample that is used. You should first be able to identify the sampling procedure and then evaluate its adequacy in ad- dressing the research problem and in supporting the conclusions. It will be helpful to know the strengths and weaknesses of each sampling pro- cedure, as summarized in Table 4.1.
A continuing problem in educational research, as well as in most social science research, is the use of volunteers as subjects. It is well docu- mented that volunteers differ from nonvolunteers in important ways. Volunteers tend to be better educated, higher socioeconomically, more intelligent, more in need of social approval, more sociable, more un- conventional, less authoritarian, and less conforming than
Obviously, volunteer samples may respond differently than non- volunteers because of these characteristics.
One way volunteers are used is in survey research. The researcher typically sends questionnaires to a sample of individuals and tabulates the responses of those who return them. Often the percentage of the sample returning the questionnaire will be 50 to 60 percent or even lower. In this circumstance the sample is said to be biased in that the re- sults may not be representative of the population. Thus, the nature of the results depends on the types of persons who respond, and ability to the target population is compromised. The specific effect that a biased sample has on the results depends on the nature of the study. For example, a study of the relationship between educational level and occupational success would be likely to show only a small relationship if only those who are most successful respond. Without some subjects who
are not successful in the sample,
cannot be accurately related to
the level of education. If a survey of teachers is conducted to ascertain their general knowledge and reading and writing skills, the results would probably be higher than the true case because of the tendency of volunteers to be better educated.