Calculate the standard error and margin of error for a sample proportion.
The standard error of a proportion is largest at 50 per cent and shrinks toward the extremes. That is why published poll margins usually quote the worst case, which applies regardless of the actual result. A 1,000-person poll has a worst-case margin of about ±3.1 points, which is why small changes between polls are usually noise.
Standard Error of Proportion
SE = √(p(1−p) ÷ n); margin of error = z × SE
SE = √(p(1−p) ÷ n); margin of error = z × SE The standard error of a proportion is largest at 50 per cent and shrinks toward the extremes. That is why published poll margins usually quote the worst case, which applies regardless of the actual result.
A 1,000-person poll has a worst-case margin of about ±3.1 points, which is why small changes between polls are usually noise.
This calculator takes 3 inputs: Sample proportion, Sample size, Confidence level. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.