Descriptive statistics

What are measures of central tendency?

Averages showing where the data clusters

How is the mean calculated?

Add all scores and divide by the number of scores

How is the median found?

Order the scores and take the middle (average the two middle values if there is an even number)

What is the mode?

The most frequent score

What is a strength of the mean?

Most sensitive as it uses all scores

What are weaknesses of the mean?

Distorted by outliers and only suitable for interval data

What is a strength of the median?

Not distorted by outliers and better for skewed data

What is a weakness of the median?

Less sensitive as it ignores most scores

Which levels of data can the median be used with?

Ordinal and interval

What is a strength of the mode?

Can be used with all data including nominal and is easy to find

What are weaknesses of the mode?

May be several or none and ignores most scores

What are measures of dispersion?

Measures of how spread out the scores are

How is the range calculated?

Largest score minus smallest score

What does a high range show?

Scores are widely spread - high participant variation

What is a strength of the range?

Easy to calculate

What are weaknesses of the range?

Affected by outliers and ignores spread between the extremes

What is standard deviation?

A measure of the average distance of scores from the mean

What does a high standard deviation show?

Scores are far from the mean so the mean is less representative

What does a low standard deviation show?

Scores cluster close to the mean - consistent results

What is a strength of standard deviation?

Uses all scores so gives the most accurate picture of variability

What is a weakness of standard deviation?

Complex to calculate

Are you expected to calculate standard deviation?

Your department pack says no - you must interpret it

What is the percentage formula?

Part divided by whole multiplied by 100

What percentage is 15 out of 20 participants?

75%

Why might a lower mean with a low standard deviation be preferred?

Improvement is more consistent for individuals (e.g. a current treatment with SD 2 versus a new one with SD 18)

What do error bars on a graph show?

One standard deviation either side of the mea