measures of dispersion

• What is range?


  the difference between minimum and the maximum values in the data set.
• The range has a significant role in describing the variability if there are no outliers.
• The range is a crude measure of the variation (spread) of the data.
• Range provides an account of the data set’s most extreme values.
• The range is easy to calculate.
• The range is extremely sensitive to outliers.
• The range doesn't use all figures so is not as accurate as standard deviation
• The range measures the two extreme values where as standard deviation measures the spread of data.
• What is the interquartile range?


  The interquartile range is a measure of statistical dispersion, which is the spread of data
• What is the best measure of the variability of skewed distributions or data sets without outliers?


  The interquartile range.
• Why is the interquartile range the best measure of the variability of skewed distributions or data sets without outliers?


  Because it’s based on values that come from the middle half of the distribution, it is unlikely to be influenced by outliers.
• The interquartile range detects the typical rage of data, detects outliers, and shows the spread of values.
• The interquartile range doesn't show the entire picture of all the data and may miss out on information, like extreme values.
• The interquartile range is better than the range as it only used middle values, which omits the extremes and therefore cannot affect the result.
• The interquartile range doesn't use all figures so not as accurate as standard deviation.
• What is standard deviation?


  it is the measure of the amount of variation of a random variable expected around its mean.
• Using statistics to compare a factor allows us to see how the spread of the data around the mean has changed and it allows us to make a judgement on how the factor has changed across the time mentioned. 
• Standard deviation gives a more accurate figure than the range or interquartile range as it considers all figures.
• Standard deviation isn't affected by extreme values
• Standard deviation measures the spread of data from the mean while the range measures the two extreme values in the data set.
• The standard deviation shows the extent of the differences from the mean
• Standard deviation doesn't consider how close together the means are between the two sets of data
• What is normal distribution?


  It occurs in a set of data in which most values cluster in the middle pf the range and the rest taper off symmetrically towards extreme values.
• What is the coefficient of variation (CV)?


  It is the spread/ratio of the standard deviation around the mean by a percentage.
• The higher the CV value:


  The greater the level of dispersion around the mean
• What does the CV allow to be compared?

  The spread of values between two different data sets that have different means.
• What is the standard error of the mean (SE)?


  it is a measure of the accuracy of the sample mean as an estimate of the limits within which the true mean lies