descriptive statistics

measures of central tendency

what the relationship is of the values with the central point / measuring the average

mean, median and mode

mean

how to calculate: add up all of the numbers then divide that by the amount of numbers

strength: good representative of the data cuz it uses every value

limitations:
- very sensitive as it can be easily distorted by extreme values
- can’t be used with nominal data that is in categories

median

how to calculate:
- order the data from smallest to largest
- work your way from the outside-in until you hit the middle
- if two values in the middle then work out the middle of those two values

strength: not affected by extreme scores

limitation: doesn’t take into account the precise value of each observation, thus doesn’t use all info available in the data

mode

how to calculate: most common value in any given set of data

strengths:
- useful for nominal data
- unaffected by extreme values

limitations:
- only useful for nominal data
- not very useful for describing data when there are multiple modes

measures of dispersion

- how dispersed or spread out the data are
- these are displayed in tables and graphs
- they help researchers understand whether scores in a data set are very similar (homogenous) or very different
- range and standard deviation

range

how to calculate: subtract the lowest value from the highest value and then add one

strength: easy to calculate

limitation: fails to take into account distribution in relation to the mean meaning it’s affected massively by extreme values as it only takes the two most extreme values into account

standard deviation (SD)

- measure of the spread of the data around the mean
- a single value that tells the researcher how far scores deviate the mean
- the larger the SD, the more spread out the data is

strengths:
- very precise as it takes into account all values
- not difficult to calculate - particularly if you have a calculator

limitation: it may hide some extreme values in the data set

raw data

- untreated numbers that researchers take from each pp
- this is the data first produced from a study