Which formula to use:

parameter Conditions/given Confidence Interval test statistic Key words Proportion nP > 5 & nQ < 5 given: population proportion (P) sample proportion (p = x/n) q=1-p & Q=1-P   Proportion Percent You are not given a standard deviation Mean population data known OR n > 30 GIVEN: σ (population standard deviation) population mean (μ)         _ sample mean: X sample size = n     You know what the population standard deviation is. Mean population data NOT known and n < 30 GIVEN: s (sample standard deviation) population mean (μ)         _ sample mean: X sample size = n     Given sample info Standard deviation OR variance(σ²) Population normally distributed GIVEN: σ (population standard deviation) sample size = n s (sample standard deviation)    You're working with a hypothesis about the standard deviation of a sample