Deciding Between z and t (1)• When we construct a confidence interval for apopulation mean, we must decide whether to use avalue of z or a value of t as the reliability factor.• To make an appropriate choice we must considersample size, whether the sampled population isnormally distributed, and whether the populationvariance is known.• Figure 6.3.3 provides a flowchart that one can useto decide quickly whether the reliability factorshould be z or t.