DB posted this on my blog and deserves an item on its own. It is how the medical establishment sweeps under the table inconvenient studies, normally known as ‘publication bias.’ What is most interesting is DB’s reference to Cancer Prevention Studies (CPS) I and II. It is data supplied by the American Cancer Society and CPS I as the basis of the BMJ published Enstrom/Kabat paper. Dr. James Enstrom had come up with the null hypothesis and was denied access to the CPS II data as a result. The results are 1.00, the null hypothesis, i.e. no correlation between passive smoking and ill health.
Conclusion.— There is a publication delay for passive smoking studies with nonsignificant results compared with those with significant results
Two approaches are used to assess publication bias in the environmental tobacco smoke/coronary heart disease (ETS/CHD) literature: (1) Statistical tests applied to all sex-specific relative risk (rr) estimates from 14 previously published studies indicate that publication bias is likely. A funnel graph of the studies′ log relative risks plotted against their standard errors is asymmetrical, and weighted regression of the studies′ log relative risks on their standard errors is significant (P < 0.01). (2) Previously unpublished ETS/CHD relative risks from the American Cancer Society′s Cancer Prevention Studies (CPS-I and CPS-II) and the National Mortality Followback Survey (NMFS) do not show an increased CHD risk associated with ETS exposure. CPS-I: men, RR = 0.97 (0.90-1.05); CPS-I: women, RR = 1.03 (0.98-1.08); CPS-II: men, RR = 0.97 (0.87-1.08); CPS-II: women, RR = 1.00, (0.88-1.14); NMFS: men, RR = 0.97 (0.73-1.28); women, RR = 0.99 (0.84-1.16). Comparison of pooled relative risk estimates from 14 previously published studies (rr = 1.29; 1.18-1.41) and unpublished results from three studies (rr = 1.00; 0.97-1.04) also indicates that published data overestimate the association of spousal smoking and CHD (χ2 = 25.1; P < 0.0001).
There is also similar evidence for publication bias in epidemiology and the overestimation of risks (22) , such as for the case of health effects from environmental tobacco smoke (7, 23) .