A2 3 practical skills: statistics decision tool and evaluation grid
A2 Biology teachers and technicians · Print and reuse all year
A printable decision tool for choosing statistical tests plus a marking grid for evaluation answers, aligned to CCEA A2 3 practical skills.
Specification: A2 3 Practical Skills in A2 Biology
Students lose A2 3 marks in two predictable places: choosing the wrong statistical test, and writing generic evaluations. These two tools address both and can be laminated for repeated use.
| The question asks about… | Data type | Test | Conclusion must state |
|---|---|---|---|
| A difference between two means | Continuous, roughly normal | t-test | Significance at p = 0.05 vs critical value |
| A relationship between two variables | Continuous pairs | Correlation coefficient | Strength, direction, and significance |
| An association between categories | Counts / frequencies | Chi-squared | Degrees of freedom and null hypothesis outcome |
| Spread around a mean | Continuous | Standard deviation / error bars | Whether error bars overlap |
Evaluation marking grid — award a mark only where all three columns are satisfied:
| Limitation named | Effect on the data stated | Specific improvement given |
|---|---|---|
| Specific to the apparatus used | Names the error type (parallax, heat loss, timing lag) | Change that removes that error, not 'more repeats' |
| Not a generic 'human error' | Says whether readings are too high or too low | Feasible with school apparatus |
- Use it as peer marking: students swap evaluations and can only award a mark when they can point to all three columns.
- Pair with any potometer, respirometer or enzyme rate practical.