Descriptive statistics

• Identify the measures of central tendency

  and explain their purpose

  Measures of central tendency = Mean, median and mode.

  Purpose: They inform researchers about the average of their data set(s).
• When is it appropriate to use the mean

  and how is it calculated?

  Used when dealing with interval data. Calculated by adding up all of the scores and dividing that number by the

  total number of scores in the data set.
• Explain one strength and one

  disadvantage of calculating the mean.


  Representative of the data set as all data is included in its calculation. Can be affected by extreme scores as these will be included in its calculation.
• When is it appropriate to use the median and how is it calculated?


  Used when dealing with ordinal data.

  Odd data: divide the number of scores by 2 and round up to get the position of the median number.

  Even data: divide the number of scores by 2. Go to the number in that position and average it with the number in

  the next higher position to get the median.
• Explain one strength and one

  disadvantage of calculating the median.


  Not affected by extreme scores as it only takes into account the middle value.

  Not representative of the entire data set as it only reflects the middle value.
• When is it appropriate to use the mode

  and how is it calculated?

  Used when dealing with nominal data.

  Count how many times each score appears in the data set. The mode is the most common number.
• Explain one strength and one disadvantage of calculating the mode.


  Not affected by extreme scores as the mode is most common value so it would not be extreme.

  There may sometimes by multiple or no modes. Also does not represent all the data as it only reflects the

  most common value.
• Identify the measures of dispersion and

  explain the purpose of calculating them.

  Measures of dispersion = range and standard deviation.

  Purpose: They inform researchers about how spread/dispersed their data is.
• When is it appropriate to use the range

  and how is it calculated?

  When examining the overall spread of the data.

  Calculated by: highest score – lowest score.
• Explain one strength and one

  disadvantage of calculating the range.


  Easy to calculate.

  Affected by extreme scores as it only uses the highest and lowest (the two extremes) of the data set.
• When is it appropriate to use the standard

  deviation?


  When examining how spread the data is around the mean. The higher the standard deviation, the greater the

  spread of data around the mean.
• Explain one strength and one disadvantage of calculating the standard deviation.


  Less affected by extreme scores as it uses all of the data in its calculation so extreme scores can be ‘drowned out’.

  Takes a long time to calculate as the mean must be calculated first.