Confidence intervals for proportions

Figure 15.3 refers back to our trial where 42 out of 50 patients showed a successful outcome. Notice that the interval is asymmetrical. The asymmetry arises because possible values are more tightly constrained on one side than the other. The upper limit of the interval could not logically be greater than 100 per cent, so the upper limit cannot be far above the point estimate of 84 per cent. However, the lower limit could be anything down to 0 per cent. Confidence intervals for proportions are always asymmetrical, unless the point estimate happens to be exactly 50 per cent (as in Figure 15.2). 

Typically 50 individuals from each RNAi experiment are analyzed by DIG microscopy and the proportion of the population with faulty DTC migration compared using 95% confidence intervals for proportions (22). 

Confidence Intervals for Proportions and Related Measures of Effect Size... 

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