Michalsen et al. (2003) conducted a study to examine the effects of “leech therapy” for pain resulting from osteoarthritis of the knee. Two treatments were randomly assigned to 51 patients with osteoarthritis of the knee.

Patients in the leech treatment received 4–6 medicinal leeches applied to the soft tissue of the affected knee in a single session. The animals were left to feed ad libitum until they detached themselves, on average 70 minutes later. Patients in the control treatment were given diclofenac gel and were told to apply it twice daily to the affected area. Pain was assessed by a questionnaire given by personnel unaware of the treatments applied to each patient. The results showed that seven days after the start of treatment, pain was significantly lower in the leech group.

a. Does this study include a control group? Explain.

b. Is this an experimental study or an observational study? Explain.

c. Is this a completely randomized design or a randomized block design? Explain.

d. Which strategy for reducing bias was not adopted in this study? How might its absence have affected the results?