Question

Confidence Intervals for a Proportion

A study was conducted to measure the effect of a road culvert on the distribution of a fish species in a Blue Ridge stream in Tennessee. The research question is whether a metal pipe culvert (perched 24 cm above the stream in May-July) is blocking the upstream-downstream movements of certain fish species. A difference in the species’ proportional abundance upstream and downstream of the culvert would suggest that the structure may be a barrier to movement. Creek Chub (Semotilus atromaculatus) were collected at a stream site by electrofishing in two sampling enclosures (each 150 m in length) – one upstream and one downstream of a pipe culvert – spaced 120 m apart.

A total of 50 fish was collected: 12 upstream of the culvert and 38 downstream of the culvert.

Use SAS to calculate 95% confidence intervals for the proportions of fish upstream and downstream of the culvert. In your bar graph, present the two proportions with the respective 95% confidence intervals.

Answer 1

Z for 99% confidence interval = Z_0.005 = 2.58

p = 200 / 400 = 0.5

n = 400

confidence interval

                                

                                = (0.5 + 0.065)

                                = (0.565 , 0.435)

Option-2) [0.565 , 0.435]