What are the degrees of freedom (labelled YYYY in Table 18.3) for the chi‐squared test of heterogeneity?

A. 1 B. 2 C. 3 D. 4 E. 5

Table 18.3

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MI No treatment 95% CI Study n N n N Weight RR Lower Upper 1 3 284 31 4.2 0.83 0.2 3.39 2 48 235 49 199 67.3 0.83 0.58 1.18 34 3 3 27 0 28 1 7.25 0.39 134.07 19 77 18 59 27.5 XXXX 0.47 1.4 Total 73 367 71 317 100 0.84 0.63 1.12 Heterogeneity chi-squared = 2.16 (df = YYYY) P = 0.54. I (variation in RR attributable to heterogeneity) = 0% Estimate of between-study variance tau-squared = 0. Test for overall effect: Z = 1.18, p = 0.24.