Descriptive Statistics

what are the three measures of central tendency?

mean, mode and median

what are the strengths of means?

• most sensitive of the measures of central tendency (it includes all the scores/values in a data set)

• more representative of the data as a whole

what are weaknesses of means?

can be distorted by extreme values resulting in an incorrect average

what are the strengths of a median?

• extreme scores don't affect it

• easy to calculate

what is a weakness of the median?

less sensitive than the mean as the actual values of lower/higher numbers are ignored and extreme values may be important

what is a strength of the mode?

easiest to calculate

what are weaknesses of modes?

• not representative of the whole data set

• not useful if there are multiple modes

what are the two measures of dispersion?

range and standard deviation

how do you calculate the range?

• take the lowest value from a data set, take it away from the highest value and add one

• e.g. (17-5) + 1 = 13

• we add one as a mathematical correct that allows for the fact that raw scores are often rounded

what is a strength of the range?

easy to calculate

what are weaknesses of the range?

• unrepresentative of the data set as a whole (only uses two most extreme values)

• doesn't indicate whether most numbers are closely grouped around the mean or spread out

what is standard deviation?

• single value that tell us how far scores deviate (move away) from the mean

• the larger the standard deviation, the greater the spread within a set of data

• if we're talking about a particular condition within an experiment, a large standard deviation suggests that not all participants were affected by the IV in the same way

• low standard deviation values reflect the fact that the data is tightly clustered around the mean (they all reacted the same way)

what is a strength of standard deviation?

it's more precise measure of dispersion as it includes all values within the final calculation

what is a weakness of standard deviation?

• can be distorted by a single extreme value

• also extreme values may not be revealed unlike with the range