5. No. The data from the double-blind study are more reliable, and suggest that the results from the single-blind were biased.

7. (a) This is an observational study, so confounding may be a problem.

(b) Rates of cervical cancer go up with age; women of different marital status have different patterns of sexual activity, and are therefore exposed to different kinds of risk; similarly for education. In other words, these are potential confounders.

(c) Pill users are more active sexually than non-users, and have more partners. That seems to be what makes the rate of cervical cancer higher among pill users. (This is like

example 2 on p.16 or exercise 11 on p. 23.)

(d) No; see (c).

10. (a) Observational study.

(b) Yes.

(c) Yes.

(d) No--the gene would also have to be associated with controlling behavior by the mother (p. 20). (e) Mothers who see their children over-eating might react in a way that psychologists would interpret as "controlling" behavior--Johnny, stop eating!

(f) No. The Chronicle seems to have over-reacted.

12. False; the conclusion does not follow. This is just like the admissions study (pp. 17ff). The Democrats may be concentrated in wards with low turnouts. Here is an example, with only two wards (and see exercise 13 on p. 24):

 4. (a) 25%

(b) 99%

(c) 140-150 mm

(d) 135-140mm

(e) About 5 x 2.1 = 10.5%

(f) 102-103 mm

(g) 117-118 mm is a good guess; the interval is somewhere between 115 and 120 mm.

6. (i) and (ii) not (iii). Reason: With lists (i) and (ii), 25% of the people have heights between 66.5 inches and 67.5 inches; 50% between 67.5 and 68.5 inches; 25% between 68.5 and 69.5 inches. Not so with list (iii).

7. (i) Natural causes. (ii) Trauma. Reason: Young people die of accidents, murder, etc.; old people die of heart disease, cancer, etc.

12. False. There are very few days where the temperature is above 90 degrees; the investigators should have looked at the number of riots divided by the number of days in each temperature range.