Geoff Sayer <[EMAIL PROTECTED]> wrote: > 3. The statistical power of the study - which would require greater > detail > of the occurrence of events. The 1200 odd GPs (Computers: 1069 vs Non > computers: 188) only provided 100 consecutive encounters. Some of these > quality indicators may not have the power to show an association if it > is a small one. > > Depression occurs at 1.9 per 100 encs (from most recent report) thereby > it is expected that there are 357 depression encounters in the Non-Computer > GP group. You then put several factors into a multivariate analysis the > statistical power is reduced again if there is in fact a real but small > difference between the two groups.
>From my reading of the abstract and the actual presentation, my guess is that >the analysis was done at the GP level i.e. they fitted a linear regression >model to the number (or percentage, since there were 100 patients per GP >presumably) of patients for each GP receiving each of the "quality indicators" >. Thus there may well be precision and power issues if only 188 of the GPs >were not computer users. Hmmm, but hold on - they report "adjusted odds >ratios", which suggests that they fitted a logistic model (which is a type of >generalised linear regression model and thus more or less consistent with the >way the study was reported) - if so, then the model really does need to take >account of the cluster sample design - there will be a lot of correlation >between patients seen by the same GP and hence the "design effect" is likely >to be large, which further reduces the precision of the parameter estimates >(and adjusted odds ratios) from the model. It is not obvious that a model whi! ch accounted for the sample design was used. Or they could have used multilevel modelling, which is probably even better, but trickier. Would be interesting to know what type of model was fitted to what data, and if sub-optimal, to repeat the analysis using statistical methods which make the most of the collected data while also taking into account the sample design. Tim C _______________________________________________ Gpcg_talk mailing list [email protected] http://ozdocit.org/cgi-bin/mailman/listinfo/gpcg_talk
