The data of Groenvold et al. (1995), summarised in Table 6.2, can be collapsed into 2x2 tables, as in Table 6.3.

Using equations (6.5) and (6.6) we calculate the expected value and variance of a, and the OR for each table, giving Table 6.4.

The three odds ratios are less than 1, reflecting that at all levels of PF there were fewer patients in the older age group who were limited to having to stay in a bed or chair. From Equation (6.8), ORMH - 0.306. Applying equation (6.7), the Mantel-Haenszel statistic is 6.65. Table T3 for x2> with df = 1, shows this to be statistically significant (p- 0.0099). Groenvold et al. report a slightly smaller p-value when using partial-gamma, but the Mantel-Haenszel test is regarded as sensitive and the difference between the two results is small.

Table 6.3 DIF analysis of the number of patients having to stay in bed or a chair (Data corresponding to Table 6.2)

Physical functioning score (PF)

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