How can the ‘central tendency’ of data be measured (50% of marks)? How is the ‘degree of dispersion’ is described (50% of marks)?
There was a lack of sufficient knowledge to pass this question. The first question required a
definition of mean, median and mode and some explanation about when the use of one
would be preferred over another. One candidate gave an example of a simple data set (a set
of numbers) and calculated the mean, median & mode and explained the effect of an outlier.
This simple exercise demonstrated they had a very good understanding of the terms.
The degree of dispersion was poorly answered. A list of measures with a sentence or
equation describing each would have scored well. The list could have included range, interquartile range (and box and whisper plots), mean absolute deviation, variance and standard deviation and coefficient of variation. Not all measures needed to be discussed to pass the question. Many candidates confused standard deviation and standard error of the mean and many candidates failed to discuss ranges which are the simplest way to describe dispersion.
What follows is "a list of measures with a sentence or equation describing each", which should have "scored well".
Measures of central tendency:
Degree of dispersion: measures which describe the dispersion of data around a mean
Lecture on types of data; by Keith G. Calkins
Richards, Derek. "Types of data." Evidence-based dentistry 8.2 (2007): 57-58.