Question 2: On the CMA2 data entry screen, what is missing for the study of Brooks et al. (2004)? Why is it missing?
You should see something like this:
| Study name | Endarterectomy Events | Endarterectomy Total N | Stenting Events | Stenting Total N | Odds ratio | Log odds ratio | Std Err | I | J |
|---|---|---|---|---|---|---|---|---|---|
| Naylor 1998 | 0 | 12 | 5 | 11 | 0.047 | –3.052 | 1.554 | ||
| Wallstent 2001 | 5 | 112 | 13 | 107 | 0.338 | –1.085 | 0.545 | ||
| CAVATAS 2001 | 25 | 253 | 25 | 251 | 0.991 | –0.009 | 0.298 | ||
| Brooks 2001 | 1 | 51 | 0 | 53 | 3.178 | 1.156 | 1.645 | ||
| Brooks 2004 | 0 | 42 | 0 | 43 | |||||
| SAPPHIRE 2004 | 8 | 167 | 7 | 167 | 1.150 | 0.140 | 0.530 | ||
| EVA-3S 2006 | 10 | 262 | 25 | 265 | 0.381 | –0.965 | 0.385 | ||
| SPACE 2006 | 38 | 584 | 46 | 599 | 0.837 | –0.178 | 0.227 | ||
| BACASS 2007 | 1 | 10 | 0 | 10 | 3.316 | 1.199 | 1.693 | ||
| ICSS 2009 | 43 | 857 | 72 | 853 | 0.573 | –0.557 | 0.199 |
What I noticed was that for Brooks et al. (2004) there is no odds ratio, log odds ratio, or standard error. There is no odds ratio because there are no events in either group. Hence there is no information about the treatment difference and we cannot estimate an odds ratio.
If you put just one event in either of the groups, CMA2 will produce something, as it has for Brooks 2001 and BACASS, each of which have only one event, for endarterectomy, and for Naylor 1998, which has events only for stenting. The standard errors for these log odds ratios are large, because they are poorly estimated.
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Last updated: 19 February, 2010.