measures of dispersion

• measures of dispersion

  = describe the spread of scores rather than their average.
• Range

  = subtract the lowest score from the highest score and add 1.

  • easy to calculate
  • only takes account of the two most extreme scores, unrepresentative of the whole data.
• standard deviation

  = more sophisticated measure which tells us how far the scores deviate from the mean, the larger standard deviation the greater the spread of scores.

  -a large standard deviation suggests not all participants were affected by the IV.

  -low standard deviation suggests all participants responded in a fairly similar way

  • includes all scores, more precise measure.
  • can be distorted by extreme score.
• Bell curve= represents a normal distribution of scores on a test, where scores are distributed evenly around the mean.