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Appendix D: Technical Details of Power Calculations and Meta-Analyses
Pages 337-346

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From page 337...
... This appendix describes and illustrates the power calculation methods used by the committee to take account of the diverse statistical methods used in the studies on which the analyses are based. The results of epidemiologic studies are generally reported in terms of relative risks (RRs)
From page 338...
... Thus, a relatively large increase in the risk of afebrile seizures could have gone unde TABLE D-1 Power Calculations for the SONIC Study Relating DPT Use to Afebrile Seizures PowerC Time Period RR Upper CIa 6b 50% 80% Within 7 days 0.5 1.5 0.56 3.00 4.80 Within 14 days 0.8 1.5 0.32 1.88 2.45 Within 28 days 0.6 1.1 0.31 1.83 2.38 aCI, Confidence interval. bo, Standard error.
From page 339...
... A different approach was taken to calculate the power of the statistical tests used in a retrospective epidemiologic study by Shields and colleagues (1988~. As described in Chapters 4 and 5 of this report, Shields and colleagues ascertained the age distribution of cases of SIDS and of a number of necrologic disorders in Denmark during two time periods with different vaccination schedules.
From page 340...
... But, because only four of the studies correct for the age pattern of SIDS (which would lead one to expect more SIDS cases in the first few days after vaccination than a uniform distribution would predict) , an additional step was needed to adjust data from the poorly controlled studies.
From page 341...
... For the other three studies, the committee calculated standard errors without taking into account the matching and other variance reduction techniques that were actually used in the study. This implies that the resulting confidence intervals overstate the true uncertainty, again by an unknown amount.
From page 342...
... This change made very little difference in the results. Thus, although the results depend somewhat on the statistical assump tions, in no case is there a significantly elevated average odds ratio for the
From page 343...
... b. Similar results comparing SIDS deaths in the early period with deaths in the late period plus deaths after the end of the first month postvaccination.
From page 344...
... The estimate of the total incidence in the 2 days postvaccination based on the data in all eight studies is 6.57 cases/864,041 children = 7.6 cases per million vaccinated children. To determine the relative and attributable risks of encephalopathy following DPT immunization, the background incidence rate was estimated as follows.
From page 345...
... , the total incidence in the week following vaccination is 2 cases per 173,771 children = 11 ~ cases her million vaccinated children. - rid Using a background rate of 0.43 x 7/2 per million = 1.5 per million, the RR estimate is 7.6 and the attributable risk estimate is 3.3 per million immunizations.
From page 346...
... 1987. Diphtheria-tetanus-pertussis immunization and sudden infant death: results of the National Institute of Child Health and Human Development Cooperative Epidemiological Study of Sudden Infant Death Syndrome Risk Factors.


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