I read about the following experiment in a recent NYTimes article. Researchers were interested in the effect of cellphone use on an individual’s willingness to assist others. On a street in Manhattan a man (apparently) using crutches dropped his newspaper and had obvious difficulty picking it up. An observer recorded whether a person passing the man was (a) on a cellphone, and (b) whether or not the person retrieved the man’s newspaper for him. Over the course of a week, this scenario was repeated many times. Of the 48 people who were on a cellphone, 19 retrieved the newspaper. Of the 205 people who were not on a cellphone, 134 retrieved the newspaper.

(a) Write a null and a two-sided alternative hypothesis in this case. Define the two parameters of interest as best you can.

(b) What are the explanatory and the response variables in this case?

(c) Construct a contingency table for these data with the rows being the categories for the response variable.

(d) Compute the appropriate sample percentages and write a brief summary of your results. Does the difference in the sample percentages seem to be of practical importance? Explain.

(e) Compute the p-value in this case.