Descriptive Statistics

1
DescriptiveStatistics

• Advanced Higher Geography

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Descriptive statistics include

• Types of data
• Measures of central tendency
• Measures of dispersion

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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 and hamlet).

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Types of data (2)

• Interval data data with no true zero. Very
  uncommon so dont worry about it.
• Ratio data most numerical data.

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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.

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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).

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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.

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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.

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Task
5 mins

• 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
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answers
Mean 5
Mode 4
Median 4
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Groups of data

• Sometimes the data we collect are in group form.

• Finding the mean is slightly more difficult. We
  use the midpoint of the group and multiply this
  by the frequency.

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Calculating the mean
265 30
8.8
The mean is ?(fx) n
Which is in the 5 9 group
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Calculating the mode
We cannot find the mode for grouped data but we
can find the modal group. The modal group is the
group that occurs most frequently- (ie 5-9
group).
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Your turn

• Read page 25 29 what we have just been
  talking about.
• Answer questions 1 and 2 from Task 4 in the books.

10 mins