Introductory Biostatistics

d¼average di¤erence

¼

31

12

¼ 2 :58 mmHg

sd^2 ¼

185 
ð 31 Þ^2 = 12

11

¼ 9 : 54

sd¼ 3 : 09

SEðdÞ¼

3 : 09

ffiffiffiffiffi

12

p

¼ 0 : 89

t¼

2 : 58

0 : 89

¼ 2 : 90

Using the column corresponding to the upper tail area of 0.05 in Appendix C,

we have a tabulated value of 1.796 for 11 df. Since

t¼ 2 : 90 > 2 : 201

we conclude that the null hypothesis of no blood pressure change should be

rejected at the 0.05 level; there is enough evidence to support the hypothesis of

increasedsystolic blood pressure (one-sided alternative).

Example 7.4 Data in epidemiologic studies are sometimes self-reported.

Screening data from the hypertension detection and follow-up program in

Minneapolis, Minnesota (1973–1974) provided an opportunity to evaluate the

accuracy of self-reported height and weight. Table 7.3 gives the percent dis-

crepancy between self-reported and measured height:

x¼

self-reported height
measured height

measured height

100%

TABLE 7.3

Men Women

Education n Mean SD n Mean SD

aHigh school 476 1.38 1.53 323 0.66 1.53
bCollege 192 1.04 1.31 62 0.41 1.46

252 COMPARISON OF POPULATION MEANS