Two cases are comparable only when they measure the same thing on a fair scale. When they do not, say so, adjust where you can, and state what the comparison cannot show.
This lesson uses the verified notes from checking place, date and source and the linked chains from causes, impacts and responses.
What should you check before comparing?
Run four checks.
- Is it the same measure, such as deaths or homes flooded?
- Is it the same kind of event, such as a river flood and a coastal flood?
- Is the time frame similar?
- Is the population or area of similar size?
If a check fails, convert to a rate where possible and add a caveat. The evidence ledger has a field for exactly that note.
Worked example
All data invented. Case A is a coastal town with 20,000 people, where a storm surge killed 40. Case B is an inland city with 500,000 people, where a river flood killed 55.
Step 1, raw totals. B has more deaths (55 against 40). That seems to make B worse.
Step 2, same scale. Convert to deaths per 100,000.
- A: 40 ÷ 20,000 = 0.002, and 0.002 × 100,000 = 200 per 100,000.
- B: 55 ÷ 500,000 = 0.00011, and 0.00011 × 100,000 = 11 per 100,000.
Step 3, interpret. Per person, A was far harder hit. 200 ÷ 11 is about 18, so the rate in A was roughly 18 times that in B.
Step 4, add the caveats. A storm surge and a river flood are different hazards, the years differ, and one event in each place is a small sample. The comparison shows the burden on each community, not which hazard is more dangerous.
The mistake to watch for
The common slip is to compare raw totals and conclude without any caveat.
Mistaken line: “Case B was worse because 55 people died compared with 40.”
The sentence ignores that B has 25 times as many people.
The correction is to use the rate and name the limit: “Per 100,000 people, Case A was far higher at 200 against 11, although the hazards and years differ.”
Check yourself
1. Case C: 12 deaths among 6,000 people. Case D: 30 deaths among 150,000 people. Compare per 100,000.
Show answer
C: 12 ÷ 6,000 × 100,000 = 200. D: 30 ÷ 150,000 × 100,000 = 20. C is ten times D per person.
2. One case is a flood 2 m deep and another is a flood 0.5 m deep. Name a reason their impacts may not be comparable.
Show answer
The events differ in size. A 2 m flood damages homes and roads far more, so the difference in impact may come from the event, not the community.
3. Give one caveat to add to any two-case comparison.
Show answer
For example: “Each case is one event in one year, so this comparison cannot show a long-term pattern.”
Where this leads next
Fair comparison needs notes that can change when new facts arrive, so continue with updating a case without rewriting history. The statistics and distribution explorer will help with rates. If comparison questions cost you marks, online one-to-one Geography tuition can give you more practice.