Descriptive statistics

• What are descriptive statistics?


  The use of graphs, tables and summary statistics to identify trends and analyse sets of data
• What are measures of central tendency?


  A descriptive statistic that provides information about an 'average' value for a data set
• What are three measures of central tendency?


  Mean, median and mode
• What is the mean?


  The arithmetic average of a data set that takes the exact values of all the data into account
• What is the median?


  The middle value of a data set when the items are placed in rank oder (from lowest to highest)
• What is the mode?


  The most frequently occurring value in a set of data
• What are measures of dispersion?


  A descriptive statistic that provides information about how spread out a set of data are.
• What are two measures of dispersion?


  Range and standard deviation
• What is the range?


  The difference between the highest and lowest item in a data set - usually 1 is added as a mathematical correction
• What is standard deviation?


  - A more sophisticated measure of dispersion which tells us how much scores deviate from the mean

  - All differences are added up and divided by the number of scores

  - This gives variance and then this is square rooted
• What is a strength of using the mean?


  Most sensitive measure of central tendency - takes account of exact distance between all the values of all the data
• What is a limitation of using the mean?


  Easily distorted by extreme values = misrepresentative of the data as a whole
• What is a strength of using the median?


  Not affected by extreme scores and easy to calculate
• What is a limitation of using the median?


  Less sensitive than the mean - not all items are included in the final calculation (such as outliers/extreme scores)
• What is a strength of using the mode?


  More useful for nominal (categorical) data
• What is a limitation of using the mode?


  Not always representative of the whole data
• What is a strength of using the range?


  Easy to calculate
• What is a limitation of using the range?


  Only takes into account the two most extreme values - fails to take into account the distribution of the numbers
• What is a strength of using standard deviation?


  A precise measure of dispersion - takes all the exact values into account
• What is a limitation of using standard deviation?


  Can be distorted by extreme values