Measure of dispersion

• What are measures of dispersion based on?

  The spread of scores
• What two measures of dispersion will be focused on?

  Range and standard deviation
• How is the range calculated?

  • Subtract the lowest value from the highest value
  • Usually add 1 to the result
• What is the range for the data set with highest value 17 and lowest value 5?

  13
• Why is 1 added to the range calculation?

  To account for rounding errors in raw scores
• If a task takes 45 seconds, what is the possible range of time taken?

  44.5 to 45.5 seconds
• What is an advantage of using the range?

  It is easy to calculate
• What is a disadvantage of the range?

  It only considers extreme values
• How can outliers affect the range?

  They can distort the representation of data
• What does the range not indicate about the data?

  How closely numbers are grouped around the mean
• What is the standard deviation?

  • A measure of how far scores deviate from the mean
  • Indicates the spread of data
• What does a larger standard deviation indicate?

  Greater dispersion within the data set
• What does a low standard deviation suggest?

  Data is tightly clustered around the mean
• Why is standard deviation considered more precise than range?

  It includes all values in the calculation
• How can standard deviation be distorted?

  By a single extreme value
• What is a limitation of standard deviation compared to range?

  Extreme values may not be revealed