Measures of central tendency and dispersion

• the mean


  • calculated by adding together every score from the data set, and dividing by the number of scores

  • it can only be used with ratio and interval - level data
• the median 


  • midpoint of the scores when placed in numerical order from low to high - if there is an even number, the median is calculated by finding the mean of the middle two scores

  • can be used with ratio, interval and ordinal data
• mode 


  • most common score

  • sometimes there is no mode because no score appears more than once, or there could be two or more modes

  • with nominal data, it is the category that has the highest frequency count

  • with interval and ordinal data, it is the data item that occurs most frequently

  • if two categories have the same frequency the data gave two modes I.e. are bi-modal