Standard Deviation in A Level Geography

Standard deviation is a statistical measure that shows how spread out a set of data values is from the mean (average). In A Level Geography, it’s used to describe and compare variation in physical and human datasets, such as rainfall totals, river discharge, temperatures, sediment size, deprivation scores or migration rates.

A small standard deviation means values are closely clustered around the mean (low variability). A large standard deviation means values are widely spread (high variability).

Where will I use standard deviation in A Level Geography?
Standard deviation is useful whenever you want to compare how consistent or variable data is, for example:

• Water & Carbon Cycles: variability in rainfall, discharge, interception or soil moisture
• Coastal Systems: variability in sediment size (sorting) or beach profile measurements
• Hazards: variability in hazard frequency/magnitude (e.g. annual earthquakes, storm days)
• Global Systems & Governance / Changing Places: variability in income, deprivation, access to services, health or education
• NEA: comparing two locations, two time periods, or testing whether one site is “more variable” than another

The standard deviation formula

For AQA A Level Geography, students should be able to use the population standard deviation formula:

Key:

σ = population standard deviation
Σ = “sum of”
x = each value
x̄ = mean
n = number of values

Sample standard deviation (useful for NEA)

If your data is a sample (common in fieldwork), you may also see:

Step-by-step method for calculating standard deviation

1. Calculate the mean (x̄)
   Add all values and divide by the number of values (n).
2. Find each deviation from the mean
   Calculate x−x̄ for every value.
3. Square each deviation
   Calculate (x−x̄)² for every value.
4. Add the squared deviations
   Work out ∑(x−x̄)²
5. Divide by n
   This gives the variance.
6. Square root the variance
   This gives the standard deviation.

Worked example

River discharge recorded (cumecs):
12, 15, 14, 10, 9

1) Calculate the mean

2) Calculate deviations and squared deviations

3) Divide by n (variance)

4. Square root

Standard deviation = 2.28 cumecs

Interpretation: River discharge typically varies by about 2.28 cumecs from the mean discharge of 12 cumecs.

How to interpret standard deviation in Geography

When you interpret a standard deviation value, you should always:

• State the mean
• State the standard deviation
• Explain what it suggests about variability
• Compare two datasets if given
• Link to a geographical process

Example interpretation sentence:
“The mean rainfall is 80 mm with a standard deviation of 2 mm, suggesting rainfall is consistent from month to month. This would reduce short-term variability in river discharge and may lower the likelihood of flash flooding.”