Distributions - normal and skewed

• Characteristics of a normal distribution:

  • Produces a symmetrical, bell-shaped curve when plotted
  • Most scores are close to the mean, with progressively fewer scores at the extremes of either tail of the distribution
  • Median and mode occupy the same centre point of the curve as the mean does
• For data to be considered normally distributed:

  • 68.26% of scores lie within one standard deviation of the mean (34.13% on each side)
  • 94.55% of scores lie within two standard deviations from the mean
  • Only 4.56% of scores lie beyond two standard deviations from the mean (2.28% above or below)
• Skewed distributions:

  • Positively skewed: large proportion of scores fall below the mean
  • Negatively skewed: large proportion of scores fall after the mean
• In both skewed distributions, the mode remains at the highest point on the graph, unaffected by extreme scores