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Conditional logistic regression with within-group varying weights

wclogit[varlist] [using] [ifexp] [inexp] [{help:weight}exp] ,group(varname)[level(#)or]

DescriptionThis command maximises the partial log-likelihood for conditional logistic regression with weights that can vary within the matched set defined by the

groupoption. In calculations the Breslow likelihood as specified in the STATA manual. Note that only one case is allowed within one group so no ties are possible and that frequency weights are not allowed. In other words the dataset should be expanded to an "individual data" format.The main application for this function would be when you have inverse probability weights to correct for any bias introduced in selecting members of each group. A typical epidemiological design would be the case-cohort study where every case from a larger cohort is included in the analysis but a smaller random sample of all possible controls are included.

Options

group(varname)is not optional; it specifies the identifier variable (numeric or string) for the matched groups.

level(#)specifies the confidence level, in percent, for the confidence intervals of the coefficients; see help level.

orreports the estimated coefficients transformed to odds ratios, i.e., exp(b) rather than b. Standard errors and confidence intervals are similarly transformed. This option affects how results are displayed, not how they are estimated.ormay be specified at estimation or when redisplaying previously estimated results.

ExamplesTo analyse an "enriched" matched case control study using inverse probability weights specified in the variable

ipw..wclogit case exp [aw=ipw], or level(99) group(matchedset)

Although in this example the option used "analytical weights" [aw=ipw] it is because these seemed more natural for this command. Inverse probability weights are definitely not frequency or probability weights.

AuthorAdrian Mander, MRC Human Nutrition Research Unit, Cambridge, UK.

Email adrian.mander@mrc-hnr.cam.ac.uk

Also seeOn-line: help for clogit, stcox.