Determining Sample Size

Question 1

Estimating the Mean or Average

Answer 1

Given z, e, σ

n ≥ ((zσ)/e)^2;

where s (used to determine σ)
= √(((x-x̄)^2)/(n-1))

Question 2

Estimating the Proportion (Infinite Population) / Cochran’s Formula

Answer 2

Given z, e, p

n ≥ (z/e)^2 (p) (1-p);

where
p = x/N, or
p = 0.5 (conservative estimate)

Question 3

Slovin’s Formula

Answer 3

Given e, N; to achieve a certain confidence interval, nothing about the population is known

n ≥ (N)/(1 + N(e^2))

Question 4

Finite Population Correction

Answer 4

Given nₒ (Cochran’s sample size recommendation), N (small population size)

n ≥ (nₒ) / ((1) + ((nₒ - 1) / N))