Descriptive statistics:

• What are descriptive statistics?

  • Descriptive statistics are used to analyse quantitative data
  • Descriptive statistics include:

  1. measures of central tendency
  2. measures of dispersion
  3. how to calculate them
• What are the three types of measures of central tendency?

  • mean
  • median
  • mode
• What is the mean?

  • Arithmetic average
  • You add up all the scores and divide it by the number of scores
• What is a strength of the mean?

  • It's a sensitive measure
  • It includes all the scores/values in the data set within the calculation
  • Represents data set better than median or mode
• What is a limitation of the mean?

  • It can be unrepresentative
  • One very large or small number makes it distorted
  • The median or mode tend to not be so easily distorted
• What is the median?

  • Middle value
  • Place all the scores in ascending order and select the middle value
  • If there are two values in the middle, the mean of these will be calculated
• What is a strength of the median?

  • Less affected by extreme scores
  • The median is only focused on the middle value
  • In some cases may be more representative of the data as a whole
• What is a limitation of the median?

  • Less sensitive than the mean
  • The actual values of lower and higher numbers are ignored
  • Extreme values may be important
• What is the mode?

  • Most frequent or most common value
  • Used with categorical or nominal data
• What is a strength of the mode?

  • It's relevant to categorical data
  • When data is 'discrete', i.e represented in categories
  • Sometimes the mode is the only appropriate measure
• What is a limitation of the mode?

  • It can be an overly simple measure
  • The mode may be at one extreme
  • It is not a useful way of describing data when there are many modes
• What are measures of dispersion?

  • Provide the researcher with an indication of how spread out the data set is
  • There are two measures of dispersion

  1. range
  2. standard deviation (don't need to know how to do it)
• What is the range?

  • The difference between the highest and lowest value
  • sometimes 1 is added if values have been rounded up or down
• What are some strengths of the range?

  • It's easy to calculate
  • Arrange values in order and subtract the smallest from the largest
  • Simple formula, easier than standard deviation
• What are some limitations of the range?

  • Does not account for the distribution of the scores
  • The range does not indicate whether most numbers are closely grouped around the mean or spread out evenly
  • The standard deviation is a much better measure of dispersion in this respect
• What is standard deviation?

  • Measure of the average spread around the mean
  • The larger the standard deviation, the more spread out the data is
• What are some strengths of standard deviation?

  • More precise than the range
  • Includes all values within the calculation
  • Therefore, more accurate picture of the overall distribution of data set
• What are some limitations of Standard deviation:

  • Can be distorted by extreme values
  • Also, extreme values may not be revealed, unlike within the range