1. Descriptive Statistics
Advanced Higher Geography
Descriptive Statistics
Ollie Bray – Knox Academy, East Lothian

2. Descriptive statistics include:
Types of data
Measures of central tendency
Measures 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 Tendency
When 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 Mean
Calculating 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 finding
the mean is:
Mean = ∑x n

7. The Median
The 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.

9. Task Answers Find the mean, median and mode of the following data.
5 mins
©Microsoft Word clipart
Find the mean, median and mode of the following data.
The weekly pocket money for 9 first year pupils was found to be:
3 – 12 – 4 – 6 – 1 – 4 – 2 – 5 – 8
Answers
Mean 5
Median 4
Mode 4

10. Midpoint x frequency (fx)
Groups of data
Sometimes the data we collect are in group form.
Slope Angle (°)
Midpoint (x)
Frequency (f)
Midpoint x frequency (fx)
0-4 2 6 12
5-9 7 84
10-14
15-19 17 5 85
20-24 22
Total
n = 30
∑(fx) = 265
Finding 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 mean
Slope Angle (°)
Midpoint (x)
Frequency (f)
Midpoint x frequency (fx)
0-4 2 6 12
5-9 7 84
10-14
15-19 17 5 85
20-24 22
Total
n = 30
∑(fx) = 265
The mean is: ∑(fx)/n =
265 / 30 =
8.8
Which is in the 5 – 9 group

12. Midpoint x frequency (fx)
Calculating the mode
Slope Angle (°)
Midpoint (x)
Frequency (f)
Midpoint x frequency (fx)
0-4 2 6 12
5-9 7 84
10-14
15-19 17 5 85
20-24 22
Total
n = 30
∑(fx) = 265
We 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 turn
Read 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