Descriptive Statistics

• Descriptive statistics= methods of summarising data & there's usually two methods to do this: measures of central tendency or measures of dispersion.
• Measures of central tendency= the way the data tends to sit in the centre- mean, median, mode.
• Measures of dispersion= the way the data is spread out- range, standard deviation.
• Mean= a statistical or arithmetic average.
• Mean Evaluation:

  • Strength- most sensitive measure, taking all scores into account.
  • Weakness- can be distorted by extreme scores & can become unrepresentative of the data.
• Median= the middle score after the data is ordered.
• Median Evaluation:

  • Strength- unaffected by extreme scores, so if data has extreme scores, this is a better measure than the mean.
  • Weakness- only takes 1 or 2 scores into account & can become unrepresentative of the data.
• Mode= the most frequently occurring score.
• Mode Evaluation:

  • Strength- unaffected by extreme scores.
  • Weakness- only takes 1 or 2 scores into account & can become unrepresentative of the data.
• Measures of dispersion:

  • Gives information on the spread of the data set.
  • Spread is all about consistency (reliability), eg 2 sets of data can have the same mean but completely different levels of dispersion.
  • A lower spread indicates a more reliable set of data.
• If asked to comment on a range of standard deviation, the smaller the better- less dispersion= more reliability.
• Range= the difference between the highest & lowest score in a data set.
• Range Evaluation:

  • Strength- easily recognised/ found.
  • Weakness- if there are extreme scores, the range is inappropriate as it will be distorted & only takes into consideration the highest & lowest score.
• Standard deviation= indicates the spread in data from the mean & is the most powerful measure of dispersion as it takes all scores into account & shows how close each individual score is to the mean.
• Lower standard deviation= more consistency= higher reliability.
• Standard Deviation Evaluation:

  • Strength- takes all scores into account & is a sensitive measure.
  • Weakness- more difficult to calculate.