Measures of Central Tendency and Dispersion Flashcards
(19 cards)
measures of central tendency
- averages which give us information about the most typical values in a set of data
- mean, median, mode
how do you work out the mean?
add up all the values in a set of data and divide this figure by the total number of values
strengths of the mean
- most sensitive - includes all the values
- most representative of the data
weaknesses of the mean
- easily distorted by extreme values (anomalies) so may not be representative
- can’t be used with ordinal data
- mean value may not be an actual value in the data set
how do you work out the median?
- arrange the values from lowest to highest - the median is the middle value
- if the number of values in a data set is even, the median is halfway between the two middle values
strengths of the median
- unaffected by extreme values
- easy to calculate
- can be used with ordinal data (unlike the mean)
weakness of the median
less sensitive than the mean as not all values are included in the final calculation
how do you work out the mode?
- the most frequently occurring value
- in some data sets there might be two (bi-modal) or no mode
strengths of the mode
- very easy to calculate
- less prone to distortion by extreme values
- may be the only method you can use
weaknesses of the mode
- very crude measure
- doesn’t use all values
- there might not be a mode
- not representative of the data as a whole
measures of dispersion
- tell us about the spread of values
- how far values vary and differ from one another
- range, standard deviation
how do you calculate the range?
take away the lowest value from the highest value
strength of the range
easy to calculate
weaknesses of the range
- only takes into account the two most extreme values
- unrepresentative of the data as a whole
- doesn’t show whether values are clustered or spread evenly around the mean
what’s standard deviation?
- a single value that tells us how far scores deviate from the mean
- the higher the standard deviation, the greater the spread of scores
- a high standard deviation suggests that not all participants were affected in the same way by the IV
- a low standard deviation reflects the fact that the data is clustered around the mean
- it implies that participants responded in a similar way
strengths of standard deviation
a more precise measure of dispersion than the range as it includes all values
weaknesses of standard deviation
- more complicated to calculate
- can be distorted by extreme values
levels of measurement - which measures of central tendency and dispersion to use
nominal - mode - n/a
ordinal - median - range
interval - mean - standard deviation
why can’t mean or standard deviation be used for ordinal data?
the intervals between the units of measurement are not of equal size
