Measures of central tendency and dispersion

• Mean

  The average - add up all the scores and divide it by the number of scores.
• Strength of the mean

  Includes all the scores in the data set within the calculation, so represents data better than median or mode.
• Limitation of the mean

  May be unrepresentative as one very large or small number makes the average disorted.
• Median

  The middle value.
• Strength of the median

  Less affected by extreme scores so in some cases may be more representative.
• Limitation of the median

  The actual values of lower and higher numbers are ignored.
• Mode

  Most frequent value.
• Strength of the mode

  Relevant to categorical data.
• Limitation of the mode

  An overly simply measure so not useful when describing data.
• Range

  The difference between the highest and lowest value.
• Strength of the range

  Easy to calculate.
• Limitation of the range

  Doesn’t account for the distribution of the scores.
• Standard deviation

  A measure of the average spread around the mean.
• Strength of the standard deviation

  Includes all the values, therefore will have a more accurate picture of the overall distribution of data set.
• Limitation of standard deviation

  Can be distorted by extreme values.