A claim says what should be true. Evidence shows what was measured. A good conclusion only goes as far as the evidence allows.
This lesson is part of SPM Chemistry and links to the other consumer and industrial chemistry lessons. You can practise the same habit with the claim evidence and explanation revision desk.
What are the four steps?
Work through any product example in this order.
- Claim: what does the product or person say?
- Evidence: what was actually measured or observed?
- Fairness: did only one variable change?
- Conclusion: what does the evidence support, and what is the limit?
Step 3 is the one students skip, because convincing numbers make it easy to forget to check the test design.
Worked example: a cleaner that “works twice as fast”
An original advertisement says: “Brand A removes oil stains twice as fast as Brand B.” A student tests each brand on the same type of cloth with the same oil stain.
| Brand A | Brand B | |
|---|---|---|
| Water temperature | 50 °C | 25 °C |
| Time to remove stain | 40 s | 80 s |
Step by step, the claim is “twice as fast”. The evidence is 40 s against 80 s, and 80 ÷ 40 = 2, so the numbers match the claim.
But the fairness check fails. Brand A was used in warm water and Brand B in cool water. Since both the brand and the temperature changed, the result cannot be blamed on the brand alone.
A correct conclusion reads: “Brand A removed the stain in 40 s and Brand B in 80 s, but the water temperatures were different. The test does not show that Brand A is faster because of the cleaner. Both brands should be tested at the same temperature.”
The mistake that loses marks
The usual mistake is to accept the claim because the numbers agree. The data table is being trusted without asking how it was produced.
| Over-claimed | Supported |
|---|---|
| Brand A is twice as fast | In this test, Brand A took half the time, but two variables changed |
| A natural cleaner is safer | The label does not give evidence about safety |
Check yourself
A fictional cleaner X is said to “remove rust best”. The test used the same rust sample, the same 10 minutes and the same water temperature for cleaners X and Y. After 10 minutes, X left 20% of the rust and Y left 55%. What can be concluded?
Answer
The test is fair, because only the cleaner changed. The evidence supports the claim for this sample and time: X left less rust (20%) than Y (55%). The conclusion should not be stretched to every kind of rust or every cleaner.
What to study next
Apply the same habit to an environmental case in discussing green chemistry using specified criteria, then use the practice set.
If you want a teacher to check your conclusion wording, see online one-to-one Chemistry tuition.