I take a train to work. There are two directions in which the trains can run. One direction is where I need to go and the other direction is the opposite. I have noticed that the trains in the opposite direction run more often. I collected the data over 200 days. Of these, on 156 days, the first train I saw after arriving at the station ran in the opposite direction. Only on 44 days, the first train I saw run in the direction I needed.

(a) Is the sample (observation of several train departures from a given station in either direction) biased or unbiased?

(b) If the sample is biased, what could be the factors that make it such? How can I collect an unbiased sample?

(c) Are my observations consistent with the Null Hypothesis that trains run in both directions with equal frequency on average?