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3.7 Summary 67

to the high noise level of individual differences. In addition, larger numbers of
participants are usually required for a between-group design. The within-group
design, on the other hand, effectively isolates individual differences and, there-
fore, is a much stronger test than the between-group design. Another bonus is that
fewer participants are required. But within-group designs are more vulnerable to
learning effects and fatigue. The appropriate design method needs to be selected
based on the nature of the application, the participant, and the tasks examined in
the experiment.
All experiments strive for clean, accurate, and unbiased results. In reality, ex-
periment results are highly susceptible to bias. Biases can be attributed to five major
sources: the measurement instruments, the experiment procedure, the participants,
the experimenters, and the physical and social environment. We should try to avoid
or control biases through accurate and appropriate measurement devices and scales;
clearly defined and detailed experimental procedures; carefully recruited partici-
pants; well-trained, professional, and unbiased experimenters; and well-controlled
environments.

DISCUSSION QUESTIONS

1. Explain the differences among the three types of study: experiment, quasi-
experiment, and nonexperiment.
2. What are the major issues that need to be considered when designing
experiments?
3. What is a between-group design? Explain the advantages and disadvantages of
a between-group design.

4. What is a within-group design? Explain the advantages and disadvantages of a
within-group design.
5. When should a between-group design be considered for an experiment?

6. When should a within-group design be considered for an experiment?
7. What is the benefit of a factorial design compared to experiments that
investigate one factor at a time?

8. What is a split-plot design?
9. Explain the differences between random errors and systematic errors.
10. What are the major sources of systematic errors, or biases?
11. What can we do to reduce systematic errors in experiments?
12. Describe the typical procedure of an experiment that involves human subjects.