Descriptive Statistics (measures of central tendency and dispersion)

Question 1

What are measures of central tendency

Answer 1

Measures of central tendency are ‘averages’ which give us information about the most typical score in a set of data

Question 2

Measures of central tendency: mean

Answer 2

Add all the scores together in each condition and then divide by the number of scores
✅ includes all scores in a data set so it is more representative of the data as a whole (most sensitive)
❌ can be misleading if there are extreme values

Question 3

Measures of central tendency: median

Answer 3

The median is the middle value in a data set and is calculated by placing all the values of one condition in order and finding the mid point
✅ The median is not affected by extreme scores
✅ It is easy to calculate
❌ less sensitive than the mean as not all scores are included in the final calculation

Question 4

Measures of central tendency: mode

Answer 4

The mode is the value that is most common
✅ unaffected by extreme values, only method that can be used when data are in categories
❌ loses meaning if there is more than one mode

Question 5

When to use each measure of central tendency

Answer 5

• consider if there are any extreme scores (anomalies) if there are none use the mean
• if there is an extreme score the median id most suitable as the mean would be distorted
• mode is never the best option except if the data is in categories (discrete)

Question 6

What are measures of dispersion

Answer 6

Ways of summarising and describing data. It shows us the spread of a set of data, how far the scores vary and differ from one another. There are two types: range and standard deviation (never asked to calculate this in an exam)

Question 7

Measures of dispersion: range

Answer 7

• the difference between the smallest and largest value in a set of scores
  ✅ easy to calculate
  ❌ only takes into account the two most extreme values which may be unrepresentative of the data set as a whole
  ❌ doesn’t indicate whether most numbers are closely grouped around the mean or spread evenly

Question 8

Measures of dispersion: standard deviation

Answer 8

• a more sophisticated measure of dispersion
• a single value that tells us how far scores deviate from the mean
• a large standard deviation means a greater dispersion of data so the particpants were not affected by the IV in the same way
• a low standard deviation means a smaller dispersion of data which implies that all particpants responded in a fairly similar way
  Example of large SD: 12,12,12,1,1,2,12,1,1,6
  Example of small SD: 6,6,6,7,6,5,6,6,6,6
  Example of no SD: 6,6,6,6,6,6,6,6,6,6
  ✅ more precise than the range as it includes all values
  ❌ can be distorted by a single extreme value

Question 9

Evaluation of standard deviation

Answer 9

✅ more precise than the range as it includes all values in the final calculation
❌ can be distorted by an extreme value