A claim is supported only as far as the test compared the things named in it. Read the data, say what it shows, then say what the claim adds beyond it.
This lesson is part of chemistry in health contexts. It pairs well with the claim evidence revision desk.
How do I check a claim against data?
Ask three questions. What was compared? Was the test fair? Does the claim go beyond what was compared?
The third question catches overreaching claims, because a claim can name a comparison the test never made.
Worked example: Soap Z
An advert says: “Soap Z kills germs better than other soaps.” A school test pressed hands washed in either Soap Z or plain water onto agar plates and counted bacterial colonies after two days. Five plates were used for each.
| Plate | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Soap Z | 12 | 9 | 15 | 10 | 14 |
| Plain water | 41 | 38 | 44 | 39 | 43 |
Means. Soap Z: (12 + 9 + 15 + 10 + 14) ÷ 5 = 60 ÷ 5 = 12 colonies. Plain water: (41 + 38 + 44 + 39 + 43) ÷ 5 = 205 ÷ 5 = 41 colonies.
Model answer. The mean colony count after Soap Z (12) is lower than after plain water (41), so in this test Soap Z reduced bacterial growth compared with plain water. The test did not include any other soap, so the claim that Soap Z works better than other soaps is not supported. This assumes the same contact time and the same hands for every plate.
The mistake that costs marks
Students copy the advert: “The data proves Soap Z kills germs better than other soaps”. The data sounds like the claim, but no other soap appears in the table.
| Statement | Supported by the table? |
|---|---|
| Soap Z gave fewer colonies than plain water | Yes, 12 against 41 |
| Soap Z is better than other soaps | No, no other soap tested |
| Soap Z kills all germs | No, colonies still grew |
Check yourself
A second test compares Soap Z and Soap Y, with mean colony counts of 12 and 11. Does this show Soap Y is better?
Answer
Not reliably. The difference is 1 colony, which is small compared with the variation between plates in the first table, where Soap Z readings ranged from 9 to 15.
The data shows the two soaps gave similar results in this test. It would need more trials to show a difference.
What to study next
Continue with explaining medicine categories at curriculum level to build vocabulary. Then read recognising the limits of a classroom example.
For a teacher to go through claim-matching with you, see online one-to-one Science tuition.