PYB110 Week Two Revision Notes
Measures of Central Tendency
The Mean Formula for Calculating
The mean is the average score. It is typical or representative of the
overall data. the Mean
It is calculated by adding the sum of all scores and dividing by the X
number of scores. M
The mean is the best way for us to estimate the unknown score of an N
The mean is influenced by every score in a distribution. Therefore, it represents all scores
but because of this can be influenced by outliers. This can lead to biased means.
There should be equal distance between the total of all mean scores above the mean and
below the mean. Therefore it is like a ‘balancing’ point.
The mean can end up being a value or score which does not exist in the original scores.
The mode is the most common score in a unimodal distribution (normal one peak
It is represented as the peak in a histogram or frequency polygon.
It is useful only when a few possible values are given as it only describes one score.
The median is the middle score that is evident after all scores have been ranked numerically.
It is easy to identify if there are an odd number of scores as it will always be the middle
If there is an even number of scores it will fall halfway between the two middle scores and
will include a .5 of a score.
The median is sometimes a better measure of central tendency than the mean because in
the case of skewed distributions, the mean can be distorted by outliers.
Which Central Tendency Measure Do I Choose?
How many values are there?
o If only a few – consider the mode.
o If more than a few – consider either the mean or median.
Shape of the distribution?
o If the data is significantly skewed – consider the median.
o If the data is symmetrical – consider the mean. This