Centre stratified: | |
ID4 | Would normally analyse together but adjust for stratification factors (which normally include centres) in analysis. |
ID7 | There will be instances where we have combined centres at the analysis stage due to small numbers. |
ID8 | Different statisticians/trials do different things. Often site = fixed effect and course within site = random effect. If too few within site, then would combine. |
ID14 | Retain structure at analysis. |
ID15 | Have grouped by region/country where numbers are small. Any adjustment should be documented in the Statistical Analysis Plan, and final decision regarding appropriateness can be discussed during blind review of data. |
ID30 | Have used both pre-specified and ad hoc approaches (due to recruitment issues). |
Not stratified by centre: | |
ID32 | We either include as a stratification factor (small number of centres, large patient numbers) or by including centre/provider as a cluster. |
Treatment provider stratified: | |
ID7 | Thinking about complex intervention studies, we don’t usually allow for a ’provider’ effect in the primary analyses, although not necessarily explicitly stated in protocol—many of these studies effectively have partial clustering. We’ve had recent interesting discussions regarding provider effect in such trials, with Chief Investigators strongly feeling that with standardised/manualised intervention and training, it isn’t relevant. |
ID15 | Any adjustment should be documented in the Statistical Analysis Plan, and final decision regarding appropriateness can be discussed during blind review of data. |
ID24 | Experience with multiple treatment providers is in oncology trials with different doctors delivering protocol treatment, e.g. chemotherapy/radiotherapy. The actual treating doctor has not been recorded on the Case Report Forms, hence all providers implicitly combined within a centre. |
ID30 | Have used both pre-specified and ad hoc approaches (due to recruitment issues). |
ID39 | Treatment providers combined by default—as we don’t routinely distinguish them in the analysis. |