= Solution
Specify the expected control-group event probability at the chosen follow-up time, the intervention probability or smallest clinically important absolute reduction to detect, the primary test's <significance level> and whether it is one- or two-sided, the desired <statistical power>, and the allocation ratio. <Statistical power> is the <probability> of rejecting the <null hypothesis> under that specified alternative; its complement is the <Type II error> probability.
For two independent binary-outcome groups, these probabilities determine the response <variances> needed by the sample-size calculation. Also specify how much loss to follow-up is anticipated when converting the required evaluable sample into a recruitment target. Here the design is balanced and the stated primary <significance level> is $0.05$. A target <statistical power> such as $80\%$ or $90\%$ and the anticipated event <probabilities> cannot be recovered from the <sample size> alone, so they should not be invented. The recruitment inflation allows for attrition rather than changing the target effect.
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