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Figure 1 | BMC Medical Research Methodology

Figure 1

From: A simple method for analyzing data from a randomized trial with a missing binary outcome

Figure 1

BK-plot of bias from an unobserved binary covariate among subjects not missing outcome. The upper diagonal line is the probability of outcome among subjects not missing outcome in randomization group Z = 1. The lower diagonal line is the probability of outcome among subjects not missing outcome in randomization group group Z = 0. For subjects in group 0, the fraction with X = 1 is φ0s and the probability of outcome is indicated by point A. For subjects in group 1, the fraction with X = 1 is φ1s and the probability of outcome is indicated by point B. The true treatment effect Δ s is the difference between the diagonal lines. The apparent treatment effect Δ s is the vertical distance between points A and B, which equals Δ + ψ s ε s , where ε s = φ1s - φ0s and ψ s = α1s - α0s = the slope of each diagonal line. To bound the overall bias Σ s ψ s ε s pr(S = s), we specify an upper bound for ε s based only on the fraction missing and a plausible value for the maximum of ψ s based on the estimates of ψ s if an observed covariate were missing.

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