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Old 01-01-2013
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Question Biostat question mean,median and mode

In a medical class of 147 students, the distribution of scores on a biochemistry final examination has a mean equal to 67,a median equal to 76, a mode equal to 80, a standard deviation equal to 5.5 and a variance equal to 30.25. Three students were unable to take the test on the scheduled date and were given a different form of the exam one week later.Which parameter is most likely to be the least biased estimator of central tendency for this distribution of biochemistry test scores?

A.Mean
B.Median
C.Mode
D.Standard deviation
E.Variance
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Old 01-01-2013
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mode.

the mode is least influenced by outliers.
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C. Mode.

Least affected
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Old 01-02-2013
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Mode remains unaffected !
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Mode. It is the least affected one
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Old 01-03-2013
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Correct Answer B Median

The correct Answer is B Median

In any normal distribution, the mean is conventionally used to represent central tendency. Recall that in a normal distribution,the mean (arithmetic average), median (the most common score) and mode (the most common score) are all the same value. This means that the distribution described in this question is not nomal,but negatively skewed. We can tell that the distribution is negatively skewed because the mean is less than the median (mean <median). Because the mean (Choice A) is overly sensitive to extreme values, in a skewed distribution the median is a better representation of central tendency than the mean.

The mode (choice C) is generally only used to represent central tendency when the distribution is excessively skewed, such as when close to 50% of the students received the same score.

The standard deviation (choice D) provided an assessment of variation or spread of the distribution and is of no help in defining central tendency.

The variance (Choice E) is computed by taking the square of the standard deviation. Like the standard deviation,it is a measure of variation, not central tendency.
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