## Chapter 31. Statistics

What is the mode in the following data set?

1, 1, 1, 1, 1, 1, 3, 4, 5, 5, 5, 5, 5, 7, 8, 8, 8?

A. 1

B. 3

C. 4

D. 5

E. 8

Answer: A. Mode is the most common value in the data set; in this case, there are 6 value 1s.

What is the median in the following data set?

1, 1, 1, 1, 1, 1, 3, 4, 5, 5, 5, 5, 5, 7, 8, 8, 8?

A. 1

B. 3

C. 4

D. 5

E. 8

Answer: D. Median is the value that divides the distribution of the data set. There are 17 numbers in the data set; the ninth number (the middle number that divides the data set in half) in the data set is 5. In case of even numbers of values in a data set, the mean of the 2 values that divide the data set would be the median. For example, the median of the data set 1, 1, 3, 5 would be (1 + 3) / 2 = 2.

A university research student wishes to study possible risk factors for disease X and decides to collect and compare the medical histories of 200 disease X patients within his institution in the last 10 years and compare this with 200 other patients with similar age group, demography, and ethnicity but disease X free. What type of study is this?

A. Case series

B. Case-control

C. Prospective cohort

D. Randomized control studies

Answer: B. This is a case-control study; the study is predefining disease X cases versus non-disease X cases and trying to identify possible risk factors.

What level of evidence would the scenario in question 3 provide?

A. Level I

B. Level II-1

C. Level II-2

D. Level II-3

E. Level III