Margin of Error
MoE = z × sqrt(p(1-p)/n) for a proportion. Approximation: ~1/sqrt(n).
For UK political polls (n=1,000): MoE typically 3.1%. Halve sample size, MoE rises by sqrt(2).
Worked examples
n=1,000: MoE ≈ 3.1%.
n=500: MoE ≈ 4.4%.
Frequently asked questions
Why does sample size matter so much?
Because MoE shrinks with sqrt(n). Doubling n halves MoE only by sqrt(2).