measures of central tendency and dispersion Flashcards
name the 3 measures of central tendency
mean, median and mode
name the 2 measures of dispersion
range and standard deviation
what is the mean & how do you calculate it?
the average. Calculated by adding up all the scores and dividing that by the total number of scores
evaluate the mean
most sensitive of the measures as it includes ALL of the scores. More representative of the data as a whole.
However, it is easily distorted by extreme values.
what is the median & how do you calculate it?
the middle value in a data set when scores are arranged from lowest to highest. In an even number of scores, the median is halfway between the 2 middle scores. In an odd amount of scores, its the middle value.
evaluate the median
extreme scores don’t affect it. It is easy to calculate once you have arranged the numbers.
However, it is less sensitive as the lower and higher value are ignored and extreme values may be important.
what is the mode & how do you calculate it?
the most frequently occurring value within a data set. There may be 2 modes (bi-modal) or no mode. Find the number that occurs the most times.
evaluate the mode
sometimes mode is the only measure you can use eg in lists or results that are in writing. Very crude measure as it isn’t representative of the data as a whole. The mode may be very different from the median etc. When there’s more than one, it’s not very useful.
what is the range & how do you calculate it?
simple calculation of the spread of scores and is worked out by talking the lowest score from the highest score and usually adding 1. Adding one is a mathematical correction that allows for the fact that raw scores are often rounded.
evaluate the range
it is easy to calculate.
However it only takes into account the 2 most extreme values which may be unrepresentative of the data as a whole.
what is standard deviation & how do you calculate it?
a more sophisticated measure of dispersion that is a single value that tells us how far scores deviate (move away) from the mean. The larger the SD, the greater the spread.
evaluate standard deviation
more precise measure of dispersion as it involves all values in the final calculation.
However, it can be distorted by a single value or extreme values may not be revealed.
what are descriptive statistics?
the use of graphs, tables and summary statistics to identify trends and analyse sets of data
define measures of central tendency
the general term for any measure of the average value I a. set of data
define measures of dispersion
the general term for any measure of the spread or variation in a set of scores
