Descriptive statistics

• Measures of central tendency

  derived from a data set and show what is happening on average in that data set
• Mode


  The most common score in the data set
• Mode Adv + Dis

  Adv = Not affected by outliers + can be used on nominal data

  Dis = may be more than one mode
• Median


  The middle score when the data is set in numerical order
• Median Adv + Dis

  Adv = not affected by outliers and can be used in ordinal data

  Dis = score may be meaningless if a decimal
• Mean


  The sum of the whole data set divided by the number of scores in the data set
• Mean Adv + Dis

  Adv = most powerful measure as it uses all of the data sets in its calculation + can be used in interval data

  Dis = Score may be meaningless if a decimal + affected by outliers - may not properly represent the data set
• Measures of dispersion

  derived from a data set and show the spread of scores
• Range


  The lowest score in data set subtracted from higher score
• Range Adv + Dis

  Adv = takes into account the extremes of data set + gives a simple measure of spread. Can be used in ordinal data

  Dis = Does not take into account all of the data and only the extremes
• Standard Deviation


  This is a measure of how far every score in a data set is from the mean
• Standard Deviation Adv + Dis

  Adv = most powerful measure of dispersion because all data is used in the calculation - Can be used on interval data

  Dis = This measure is more difficult to interpret than the range
• Standard deviation 6 steps:

  1. Work out the mean
  2. Take it from each score in the data test
  3. Square each difference
  4. Add together each of the squared differences
  5. Divide this by N-1
  6. Find the square root of this value + this is the standard deviation