Measures of CT & Dispersion

• What is descriptive statistics?

  The use of graphs, tables and summary statistics to identify trends and analyse sets of data.

  • describes the patterns found in a set of data
• What are measures of central tendency?

  The general term for any measure of the average value in a set of data.

  • describes an average
• What are measures of dispersion?

  The general term for any measure of the spread or variation in a set of scores.

  • describe how spread out the data is
• What are the 3 measures of central tendency?

  1. Mean
  2. Median
  3. Mode
• Evaluate the use of mean as a measure of central tendency

  • most sensitive measure of central tendency as it includes all the values in a data set

  strength:

  • representative

  limitation:

  • it’s easily distorted by extreme values
• Evaluate the use of median as a measure of central tendency

  strength:

  • extreme scores don’t affect the median

  limitation:

  • less sensitive than the mean as it doesn't account for all scores
• Evaluate the use of mode as a measure of central tendency

  • there may be two modes (bi-modal) or even no mode in a data set

  strength:

  • very easy to calculate

  limitation:

  • not representative of the data as a whole
• What are the 2 measures of dispersion?

  1. Range (highest score minus lowest score PLUS 1 - to be more inclusive)
  2. Standard deviation = a sophisticated measure of dispersion in a set of scores - it tells us by how much, on average, each score deviates from the mean
• Evaluate the use of standard deviation as a measure of dispersion

  • high standard deviation shows more variability in a set of data - suggests not all participants were affected by the IV in the same way
  • low standard deviation shows that the data is clustered around the mean, implying that all participants responded to the IV in a similar way

  strengths:

  • all scores are taken into account - more reliable
  • can be used in further analysis

  limitations:

  • takes longer to calculate
  • can be distorted by a single extreme value