12 FURTHER MATHEMATICS DISPLAYING AND DESCRIBING THE DISTRIBUTIONS

12 FURTHER MATHEMATICS DISPLAYING AND DESCRIBING THE DISTRIBUTIONS OF NUMERICAL VARIABLES

The grouped frequency distribution

The histogram

CAS CALCULATOR

Histograms

Outliers are any data values that stand out from the main body of data. These are data values that are atypically high or low.

Centre Histograms 6 to 8 display the distribution of test scores for three different classes taking the same subject. They are identical in shape, but differ in where they are located along the axis. In statistical terms we say that the distributions are ‘centred’ at different points along the axis.

Centre But what do we mean by the centre of a distribution? For the present we will take the centre to be the middle of the distribution. You might know of this point as the median. The middle of a symmetric distribution is reasonably easy to locate by eye.

Centre

Spread

Range

Example Report For these 85 countries, the distribution of the number of phones per 1000 people is positively skewed. The centre of the distribution lies between 170 and 340 phones/1000 people. The spread of the distribution is 1020 phones/1000 people. There are no outliers.

WORK TO BE COMPLETED Exercise 1 C Questions 1, 5, 7, 9