Practice Problems: Measures of Central Tendency - Answer

Midterm exam scores for a small advanced neuroanatomy class are provided below. Scores represent percent of items marked correct on the exam.

DataArray
87 99
99 94
75 93
87 88
94 87
75 87
35 87
88 75
87 75
93 35


Mean

Mean = X / N = 820 / 10 = 82.0


Median

35757587878788 939499

The median is 87. Half of the scores fall above this number and half fall below.


Mode

Mode is equal to 87. It occurs 3 times; all other scores occur only 2 times or less


What does this information tell you about students' performance on the midterm (the traditional grading scale is used)?

The mean grade on the midterm was an 82 (a low B). Half of the students had a test score above 87 (a high B or an A). Half the students' scores were lower than an 87. The most common test score was an 87 (a high B).


Is this data skewed?

Yes, this data is skewed (a negative skew). The score of 35 is an extreme score (outlier), has caused the skew, and distorts the mean.


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