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Biometrika Advance Access originally published online on September 25, 2008
Biometrika 2008 95(4):992-996; doi:10.1093/biomet/asn039
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© 2008 Biometrika Trust

Miscellanea

On the consequences of overstratification

B. L. De Stavola

London School of Hygiene and Tropical Medicine, London WC1E 7HT, U.K. bianca.destavola{at}lshtm.ac.uk

D. R. Cox

Nuffield College, Oxford OX1 1NF, U.K. david.cox{at}nuffield.ox.ac.uk

Received for publication 1 April 2008. Revision received 1 July 2008.

It is common, in particular in observational studies in epidemiology, to impose stratification to adjust for possible effects of age and other variables on the binary outcome of interest. Overstratification may lower the precision of the estimated effects of interest. Understratification risks bias. These issues are studied analytically. Asymptotic results show that loss of efficiency depends on the true effect and on a measure of the average imbalance across strata between exposed and unexposed individuals. Bias depends on the correlation between stratum-specific size imbalances and event rates in the unexposed. Approximate results are also given. An example is used.

Key Words: Bias • Conditional likelihood • Confounder • Epidemiology • Information • Logistic model: Matched pairs • Poisson distribution



References

    Andersson M., Carstensen B., Storm H. H. Mortality and cancer incidence after cerebral arteriography with or without thorotrast. Radiat. Res. (1995) 142:305–20.[CrossRef][Web of Science][Medline]

    Brookmeyer R., Liang K. Y., Linet M. Matched case-control designs and overmatched analyses. Am. J. Epidemiol. (1986) 124:693–701.[Abstract/Free Full Text]

    Cochran W. G. The effectiveness of adjusting by subclassification in removing bias in observational studies. Biometrics (1968) 24:295–313.[CrossRef][Web of Science][Medline]

    Cox D. R. Two further applications of a model for binary regression. Biometrika (1958) 45:562–5.[Free Full Text]

    Day N. E., Byar D. P., Green S. B. Overadjustment in case-control studies. Am. J. Epidemiol. (1980) 112:696–706.[Abstract/Free Full Text]

    Gail M. The effect of pooling across strata in perfectly balanced studies. Biometrics (1988) 44:151–62.[CrossRef][Web of Science]

    Mantel N., Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J. Nat. Cancer Inst. (1959) 22:719–48.[Web of Science][Medline]

    Neuhauäser M., Becher H. Improved odds ratio estimation by post-hoc stratification of case-control data. Statist. Med. (1997) 16:993–1004.[CrossRef]

    Petersen M. R., Deddens J. A. Effects of omitting a covariate in Poisson models when the data are balanced. Can. J. Statist. (2000) 28:439–45.[CrossRef]


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This Article
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Right arrow Articles by De Stavola, B. L.
Right arrow Articles by Cox, D. R.
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