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Date sent: Tue, 22 Aug 2000 03:47:22 -0400 Subject: When treatment harms From: Jeanne Lenzer <[log in to unmask]> To: "EBM (E-mail)" <[log in to unmask]> Send reply to: Jeanne Lenzer <[log in to unmask]> > Just an uneducated question, re: a listmember's query: > (snip) - "I am getting some negative RRR [with CAT snipper]. What > would be their interpretation?. I know that RRR = 0 is null effect > and RRR= 1 is cure." > > Here's my question: If - as must be presumed by the range for RRR of > 0-1 - the term RRR assesses only efficacy of intervention and not > risks of intervention - is there a number that incorporates risk of > treatment? (In other words a more global assessment of intervention > that would allow a negative outcome)? > > Without such a global value, how do we measure the many thrombolytic > trials in stroke, for example, that show more deaths with treatment > intervention than without? I am increasingly concerned by the ways > sponsored researchers do "spin control" and it seems to me that RRR is > one such term that can be so abused if the reader is not alert. For > example, an intervention that reduces a primary endpoint (fatal MI in > the pt with diabetes) but increases total death rate (from > pancreatitis/hepatitis whatever - [shades of Rezulin]) the outcome may > be spun as positive through a set of maneuvers from a.) referring to a > positive RRR (correctly) and then b.) combining endpoints (death and > disability) to a more neutral - or even positive effect (as has been > done in the thrombolytic trials). > > Have I misunderstood something here? No, I don't think so but I think there are two separate issues. First, manipulation to show "desired" effects (usually that a treatment is effective). Any of the ways of presenting treatment effects (relative risk RR, relative risk reduction RRR, numbers needed to treat NNT etc) can be manipulated like this, although some more easily than others (eg big RRRs presented for rare outcomes where NNTs are high). The main outcomes I pay attention to are those defined as primary and secondary endpoints in the methods section. If these (and other endpoints) are combined in peculiar ways to produce statistically significant results then it makes me suspicious that there's been some data dredging to find the "right" combination because the main endpoints don't show benefit. Second, I don't think there's a problem in having a negative relative risk reduction. It means treatment is worse than control for that endpoint (assuming that it's statistically significant/the confidence intervals don't cross zero). Take away the negative and call it a relative risk increase of treatment. It's usually easier to see what's happening with numbers need to treat/harm though. Bruce Bruce Guthrie, MRC Training Fellow in Health Services Research, Department of General Practice, University of Edinburgh, 20 West Richmond Street, Edinburgh EH8 9DX Tel 0131 650 9237 e-mail [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%