Introduction and methods sections reproduced from: Early Breast Cancer Trialists' Collaborative Group, "Treatment of Early Breast Cancer. Volume 1. Worldwide Evidence 1985-1990"
Oxford University Press 1990
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||Systematic public availability of randomized trial results
||Informative overviews even of somewhat different trials, despite heterogeneity of design and of size of treatment effect
||Importance of reliably assessing MODERATE treatment effects
||Two main reasons for using overviews of properly randomized trials to assess MODERATE treatment effects: avoiding selection biases and reducing random errors
||Review of many trials, with no data-dependent omissions, to limit selection bias in assessment of treatment effects
||Other selection biases either in design or in analysis of trials
||Proper randomization (with no subsequent exclusions) to limit selection bias in design of trials of moderate treatment effects
||Selection biases from subgroup analyses: statistical difficulty in the assessment of qualitative "interactions" and of quantitative "interactions"
||Specific categories of patient or of treatment: data-dependent emphasis on subgroup analyses versus indirect extrapolation of overall analyses
||Use of recurrence data, as well as mortality data, to study interactions unbiasedly
||Use of overviews to assess effects of treatment on other specific causes of early death, or other rare endpoints
||Use of overviews to improve the reliability of data from particular trials
||Summary of the inclusion criteria for trials in the present overviews
||Principles of identification of trials: selection bias may be limited even without absolute completeness
||Practice of identification of trials: multiple sources of information
||Methods of seeking data from individual trials
||Methods of checking data from individual trials
||Methods of publishing data from individual trials
||Medical assumptions: (1) modest sizes of treatment effects, and (2) differences of size but not of direction between effects in different circumstances
||Comparisons only of like with like, based on "Observed minus Expected" (O-E) differences in each separate trial
||Routine stratification of all main analyses by age (<50, 50+) and by year (1, 2, 3, 4, 5+) of follow-up
||Additional stratification of selected analyses for the available information on nodal status or Estrogen Receptor status
||Arithmetic procedures for calculation of Observed minus Expected (O-E) numbers of events among treatment-allocated patients, and for obtaining "two-sided" significance levels ( 2 P )
||Interpretation of P-values: statistical significance and medical judgement
||RESULTS OF RADIOTHERAPY TRIALS as an example of the summation of (O-E) values from different trials to provide an overall test of the "null hypothesis" of no treatment effect
||Use of (O-E) values to provide a description of the typical reduction in the odds of treatment failure (i.e. to describe the "alternative hypothesis")
||Graphical display methods for separate trial results, and for an overview
||Similarities between risk ratios, death rate ratios and odds ratios when event rates are low
||Logrank "year of death" analyses for statistical significance tests, and for estimation of reductions in annual odds of death
||Life-table estimation for descriptive purposes
||Test of heterogeneity between several different trial results
||Arithmetic details of tests for trend, for heterogeneity and for interaction
||Practical meaning of a clear effect of treatment in a single large trial
||Practical meaning of a clear effect of treatment in an overview of many trials
||Fixed-effect "assumption-free" methods, and random-effect "assumed representativeness" methods
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