2 Descriptive statistics include: Types of dataMeasures of central tendencyMeasures of dispersion
3 Types of data (1)Nominal data: data that has names. eg: rock types (sedimentary, igneous or metamorphic).Ordinal data: data that can be placed in ascending or descending order. eg: settlement type (city, town, village & hamlet).
4 Types of data (2)Interval data: data with no true zero. Very uncommon so don’t worry about it.Ratio data: most numerical data.
5 Central TendencyWhen you calculate the central tendency of a data set you calculate its average.The measurements used for calculating central tendency include the mean, the mode and the median.
6 The MeanCalculating the mean is one of the commonly used statistics in geography.It is found by totalling the values for all observations (∑x) and dividing by the total number of observations (n).The formula for findingthe mean is:Mean = ∑xn
7 The MedianThe median is the middle value when all of the data is placed in ascending / descending order.Where there are two middle values we take the average of these.
8 The Mode The mode is the number that occurs the most often. Sometimes there are two (or more) modes. Where there are two modes the data is said to be bi-modal.
10 Midpoint x frequency (fx) Groups of dataSometimes the data we collect are in group form.Slope Angle (°)Midpoint (x)Frequency (f)Midpoint x frequency (fx)0-426125-978410-1415-191758520-2422Totaln = 30∑(fx) = 265Finding the mean is slightly more difficult. We use the midpoint of the group and multiply this by the frequency.
11 Midpoint x frequency (fx) Calculating the meanSlope Angle (°)Midpoint (x)Frequency (f)Midpoint x frequency (fx)0-426125-978410-1415-191758520-2422Totaln = 30∑(fx) = 265The mean is: ∑(fx)/n =265 / 30 =8.8Which is in the 5 – 9 group
12 Midpoint x frequency (fx) Calculating the modeSlope Angle (°)Midpoint (x)Frequency (f)Midpoint x frequency (fx)0-426125-978410-1415-191758520-2422Totaln = 30∑(fx) = 265We cannot find the mode for grouped data but we can find the modal group. The modal group. The modal group is the group that occurs most frequently (ie: 5-9 group).
13 Your turnRead page 25 – 29 of ‘Geographical Measurements and Techniques: Statistical Awareness, LT Scotland, June 2000.Answer questions 1 & 2 from Task 4 in this book.10 mins