Identifying missing evidence means asking what a claim leaves out and why that matters. For sustainability claims, the gaps are usually the baseline, the total amount, the time period, the source and the effects on other resources.
This final lesson draws on every skill in food, water and energy systems, especially reading water data and comparing approaches. The statistics and distribution explorer lets you test totals and rates.
Which questions should you ask?
- Compared with what? Is there a baseline year or place?
- Rate or total? A fall per unit can still mean a rise overall.
- Over what period? One good year is not a trend.
- Who measured it, and how? Is the source or method stated?
- What else changes? Energy, soil, waste, other communities.
- Who benefits and who bears the cost?
Worked example
The data are invented for practice. A farm company says: “We have cut our water use by 20%, so our farming is now sustainable.”
The 20% hides which measure was used.
Suppose water per tonne of crop fell from 10 m³ to 8 m³, a 20% cut. Before, the farm produced 1,000 tonnes. After, it produces 2,000 tonnes.
Before. 10 × 1,000 = 10,000 m³.
After. 8 × 2,000 = 16,000 m³.
Change. 16,000 − 10,000 = 6,000 m³, and 6,000 ÷ 10,000 = 0.6, so total use rose by 60%.
Written answer. The claim reports a rate, water per tonne, not the total taken from the local source. In this example the total rose by 60% because output doubled. The claim also gives no baseline year, no source for the figures, and no evidence about the river or aquifer supplying the farm. To judge sustainability we would need total abstraction, the state of the source over several years and effects on other users.
What mistake does this lesson prevent?
Mistaken answer: “The claim is wrong because farms use a lot of water.”
This replaces evidence with an opinion. It does not use the claim’s own words, and it cannot earn credit as analysis.
The correction is to name the specific gap and say what would fill it: “The claim does not state the baseline or the total, so we cannot tell whether the 20% fall reduces pressure on the source.”
Check yourself
1. A town reports that its energy use per person fell 5%. Name one thing missing.
Show answer
The total. If the population rose by more than 5%, total energy use may have increased. The time period and baseline are also missing.
2. A poster says a wind farm is “fully sustainable”. Give two questions to test it.
Show answer
For example: What materials and energy were used to build and maintain it? What is its effect on land, wildlife and local residents? Does it supply energy all year, and how is demand met when the wind is low?
3. Rainfall was 20% above average this year and a company calls its water supply secure. What is missing?
Show answer
One year does not show a trend. The claim needs several years of data, the supply capacity and demand levels.
Where does this lead next?
Now put everything together in the mixed practice set. Record repeated slips in the mistake log so you can retest them later.
Learning to question evidence calmly takes practice with feedback, which is one thing online one-to-one Geography tuition can offer.