psychology key vocab (dispersion and distribution)

how do you calculate the mean?

add up all the scores in a data set and divide them by the total number of scores

how do you calculate the median?

Arrange the scores from lowest to highest. Identify the middle value in the data as the median. If there are two middle values, add them together and divide by two.

how do you calculate the mode?

Find the most common number.

mean - strengths

the most sensitive as it uses all the values. this makes it more representative of the entire set

mean - weaknesses

• most likely to lead to a score which is not an actual score in the set of data

• it can be unrepresentative as it is easily distorted by extreme values

median - strengths

• not affected by extreme scores

• easy to calculate

median - weaknesses

less sensitive because not all the scores are used in the calculation

mode - strengths

• very easy to calculate

• less prone to distortion by extreme values

• only measure to use when data is nominal (in categories) e.g. favourite colour

mode - weaknesses

• less sensitive because not all the scores are used in the calculation

• data can end up with none or two

how do you calculate the range?

you subtract the lowest value from the highest value

range - strengths

• easy to calculate

• takes full account of extreme values 

range - weaknesses

• distorted by extreme value

• does not show the overall spread of the data as not all data is considered

how do you calculate standard deviation?

it measures how much scores deviate from the mean by calculating the difference between the mean and each score

standard deviation - strengths

• more sensitive because all values are used in the calculation

• allows interpretation of individual scores compared to the mean

standard deviation - weaknesses

• more complicated to calculate

• can still be distorted by an extreme value (but less so than the range)

• less meaningful if data is not normally distributed (as the mean isn't in the middle)

where is the distribution concentrated in a positive skewed distribution

the left of the graph

where is the distribution concentrated in a negative skewed distribution

the right of the graph

order of median, mode, and mean in a positive skew

mode, median, mean

order of median, mode, and mean in a negative skew

mean, median, mode