Measures of dispersion

• Range - distance between the highest and the lowest value

  Strengths: simple and easy to calculate

  Limitations: doesn't take central values of data into account, can be skewed by extreme values
• Standard deviation - is a measure which shows to what extent the values in a data set deviate from the mean
• low SD reflects that data is tightly clustered around the mean which might imply all ppts responded in similar way
• Standard deviation

  Strengths: can be calculated using all values, may be more representative than range, much more precise measurement than the renge

  Limitations: use of all measurements can be distorted by extreme values
• Standard deviation tells us the average distance of each score from the mean.​

  • 68% of normally distributed data is within 1 sd each side of the mean​

  • 95% within 2 sd​

  • Almost all is within 3 sd​

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