| Situation | ME | Assumptions |
| Know sigma | (Z*)[sigma / n]^0.5 | SRS |
| Must estimate sigma, small sample size | (t*)[s / n]^0.5 | SRS, population N-distr |
| binomial--proportion | (Z*)[p(1 - p) / n]^0.5 | SRS, np >10, n(1-p) >10 |
| binomial--count or number | (Z*)[np(1 - p]^0.5 | SRS, np >10, n(1-p) >10 |