The times of UFO sightings in the United States reported to the UFO National Reporting Center during the period May 14€“31, 2014, are described by the histograms in Fig. 37 (using number of hours since midnight) and Fig. 38 (using number of hours since noon).
Fig. 37

Fig. 38

a. Explain why one distribution is unimodal and the other is bimodal. Which of the two distributions is somewhat misleading?
b. The means and medians for both distributions are shown in Fig. 39. A student thinks that the values for the medians must be wrong, because he thinks the values should be 12 hours apart, not 11 hours. What would you tell the student?
Fig. 39

c. How is it possible that the means of the two distributions differ by only approximately 6.4 hours when the medians differ by so much more (11 hours)?
d. During what three-hour time slot were there the most sightings? Do you get the same result by inspecting the two distributions?
e. Why were there so many sightings during the time slot you found in part (d)? A UFO believer explains that alien aircraft tend to approach the United States then. What is another explanation? What type(s) of bias likely occurred?

Transcribed Image Text:

Times of UFO Sightings 205 200 150 100 49 50 -40 17 15 15 5 10 5 2025 Hours since midnight Times of UFO Sightings 205 200 150 100 49 50 40 15 15 17 5 10 5 20 25 Hours since noon Summary statistics: Column n Mean Median Hours since midnight 370 16.91081121 10 Hours since noon 370 10.489189