Year 7 Science • AC9S7I06 • Homework
Evaluate scientific methods, data and claims
For every evaluation, identify the problem, explain its effect on the evidence, then give a specific improvement.
Part A • Data quality
Spread, outliers and reliability
Marble-roll times (s): 1.8, 1.7, 1.9, 3.2, 1.8, 1.7
- Identify the possible outlier and explain why it should be investigated rather than automatically deleted.
- Calculate the range of the full dataset. Then calculate the range without the possible outlier. What does this show about spread?
- Give two indicators you would use to judge whether the data are high quality.
- State one unanswered question raised by this dataset.
Part B • Method evaluation
Hidden assumptions
Method: “Place two identical plants on a windowsill. Water one with fertiliser and one with plain water. Measure height after two weeks.”
- Identify three assumptions or uncontrolled variables.
- Explain how one of these could weaken validity.
- Rewrite the method so it better controls variables and uses replicates.
- Identify one improvement that mainly increases reliability and one that mainly increases validity.
Part C • Investigation critique
Temperature and sugar dissolving
| Temperature | Trial 1 (s) | Trial 2 (s) | Trial 3 (s) |
|---|---|---|---|
| 20°C | 118 | 121 | 140 |
| 40°C | 72 | 75 | 110 |
| 60°C | 40 | 43 | 41 |
Method notes: 200 mL water, one teaspoon of sugar, “stir gently”, three trials per temperature. Temperature was set at the start of each trial but not monitored continuously.
- Compare the spread at 20°C, 40°C and 60°C. Which condition is most precise?
- Identify one possible outlier and explain what should be done next.
- Identify two assumptions in the method.
- Identify one likely random source of variation and one possible systematic source of error.
- Evaluate the claim “Higher temperature causes sugar to dissolve faster.” Use the data but acknowledge at least one limitation.
- Suggest two specific improvements and explain how each strengthens the evidence.
Part D • Conflicting evidence
Which evidence is stronger?
Set A: 10 students, no control group, average reaction-time improvement of 0.05 s.
Set B: 40 students, control group included, mixed results, with some students becoming slower.
- Which evidence set is stronger overall? Justify using at least three criteria.
- Identify one piece of conflicting evidence that prevents a simple “yes” conclusion.
- Write a cautious conclusion that matches the evidence.
Enriched evaluation
Full scientific critique
Choose one investigation above and write a complete critique covering: data quality, spread, assumptions, uncontrolled variables, random/systematic error, evidence supporting the claim, conflicting evidence, unanswered questions, and the single most important improvement.