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Biostatistics

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720 CHAPTER 13 NONPARAMETRIC AND DISTRIBUTION-FREE STATISTICS<br />

usual procedure of assigning the tied observations the mean of the ranks for which they are<br />

tied and proceed with steps 2 to 6.<br />

EXAMPLE 13.10.1<br />

In a study of the relationship between age and the EEG, data were collected on 20 subjects<br />

between ages 20 and 60 years. Table 13.10.1 shows the age and a particular EEG output<br />

value for each of the 20 subjects. The investigator wishes to know if it can be concluded that<br />

this particular EEG output is inversely correlated with age.<br />

Solution:<br />

1. Data. See Table 13.10.1.<br />

2. Assumptions. We assume that the sample available for analysis is a<br />

simple random sample and that both X and Yare measured on at least the<br />

ordinal scale.<br />

3. Hypotheses.<br />

H 0 : This EEG output and age are mutually independent.<br />

H A : There is a tendency for this EEG output to decrease with age.<br />

Suppose we let a ¼ :05.<br />

TABLE 13.10.1 Age and EEG Output<br />

Value for 20 Subjects<br />

Subject<br />

Number<br />

Age (X)<br />

EEG Output<br />

Value (Y)<br />

1 20 98<br />

2 21 75<br />

3 22 95<br />

4 24 100<br />

5 27 99<br />

6 30 65<br />

7 31 64<br />

8 33 70<br />

9 35 85<br />

10 38 74<br />

11 40 68<br />

12 42 66<br />

13 44 71<br />

14 46 62<br />

15 48 69<br />

16 51 54<br />

17 53 63<br />

18 55 52<br />

19 58 67<br />

20 60 55

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