Identify The Inference Methods Practice Test

Estimating a population mean from a small sample when the population standard deviation is unknown uses a one-sample t-interval. Here you have ten squirrels, so the degrees of freedom are n minus one, which is nine. The confidence interval for the mean is built as the sample mean plus or minus a t critical value with nine degrees of freedom times the sample standard deviation divided by the square root of the sample size. This approach accounts for the extra uncertainty introduced by estimating sigma from the sample. The z-interval would be used only if the population standard deviation were known (or the sample were very large), which isn’t the case here. The two-sample t-interval is for estimating the difference between two independent means, and the matched-pairs t-test is for paired data, not for estimating a single mean. So a one-sample t-interval with nine degrees of freedom is the appropriate method.