DS3 Summary Statistics

Basic concepts: • calculate and use the measures of location – mean, mode and median – for grouped data presented in table or graphical form including from stem-and-leaf plots and cumulative frequency polygons • determine the mean for larger data sets of either ungrouped or grouped data using the statistical functions of a calculator • describe and calculate standard deviation • select and use the appropriate statistic (mean, median or mode) to describe features of a data set, eg median house price or modal shirt size • compare summary statistics of various samples from the same population • assess the effect of outlying values on summary statistics for small data sets

Median Mean Mode

Working with a larger set of data 18 95 60 147 Mode = most common score = 21 Median = middle score, so between the 8th and the 9th score = 20

Calculator steps… ‘2’ for stats mode ‘1’ and check it looks like this Enter data, pressing ‘=‘ after each score. Use the blue wheel to go to the frequency column and enter the frequencies. Press then and see this Press ‘4’ then ‘2’ for the mean, ‘4’ then ‘3’ for the standard deviation (covered in class soon)

Standard Deviation The standard deviation is a measure of the spread of data about the mean. It is an average of the squared deviations of each score from the mean. Standard deviation is calculated from the formula shown below. In this course you only have to use a calculator to find the standard deviation.

Which measure is best to use?