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Statistical Methods in Medical Research 4ed

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18.10 Meta-analysis 647<br />

the comb<strong>in</strong>ed estimate of efficacy, ^u*, will have greater variance than the estimate<br />

y obta<strong>in</strong>ed from the fixed-effects model.<br />

A slightly more efficient procedure is to estimate by maximum likelihood,<br />

which <strong>in</strong>volves an iterative calculation (see, for <strong>in</strong>stance, Normand, 1999, equation<br />

(8)).<br />

Both these procedures are <strong>in</strong> the spirit of empirical Bayesian methods (§6.5),<br />

whereby the between-trial variation can be estimated from the available data. In<br />

contrast to this approach is the fully Bayesian analysis, <strong>in</strong> which (with the model<br />

described above) prior distributions are specified for the parameters vi, u* and<br />

v*, either based on specific prior judgements or us<strong>in</strong>g non-<strong>in</strong>formative distributions<br />

to represent ignorance (Smith et al., 1995; Normand, 1999).

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