To compare the mean number of days spent waiting to see a family doctor for two large cities, you randomly select several people in each city who have had an appointment with a family doctor. The results are shown at the left. Construct a 90% confidence interval for the difference in mean number of days spent waiting to see a family doctor for the two cities.

When the sampling distribution for x̅₁ - x̅₂ is approximated by a t-distribution and the populations have equal variances, you can construct a confidence interval for μ₁ - μ₂, as shown below.

construct the indicated confidence interval for μ₁ - μ₂. Assume the populations are approximately normal with equal variances.

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Sample Statistics for Number of Days Waiting for an Appointment with a Family Doctor Miami Seattle X1 = 28 days s1 = 39.7 days n1 = 20 X2 = 26 days s2 = 42.4 days n2 = 17 (X1 – X2) – tô • V n1 < µ1 - M2 < (x1 – x2) + te • п2 V n1 п2 (п1 1)sĩ + (n2 – 1)sź and d.f. = n1 + n2 - 2 where ở = пу + ng — 2