In an original study, a researcher investigated the effect of a new organic foliar fertilizer on the growth rate of rare orchid seedlings (measured by the increase in leaf surface area, in mm2\text{mm}^2mm2, over a 14-day period) using an independent groups design. Group 1 (12 seedlings) was treated with the organic fertilizer, while Group 2 (12 seedlings) was treated with a standard mineral fertilizer. A key limitation identified in this original study was that individual genetic variation and differences in baseline seedling health (subject variables) could have skewed the growth results.
To address this, the researcher designed a follow-up study.
The researcher obtained a sample of 12 cloned orchid seedlings of a specific micropropagated lineage. Using a repeated measures design, each orchid seedling underwent two consecutive 14-day growth cycles.
The order of the treatments was counterbalanced across the seedlings (half receiving Treatment A first, and the other half receiving Treatment B first), and the increase in leaf surface area (mm2\text{mm}^2mm2) during each 14-day cycle was recorded.
| Orchid Seedling | Treatment A (Standard) | Treatment B (Organic) |
|---|---|---|
| 1 | 38 | 45 |
| 2 | 48 | 52 |
| 3 | 30 | 31 |
| 4 | 50 | 58 |
| 5 | 35 | 40 |
| 6 | 44 | 42 |
| 7 | 41 | 49 |
| 8 | 51 | 55 |
| 9 | 32 | 36 |
| 10 | 42 | 47 |
| 11 | 37 | 39 |
| 12 | 44 | 50 |
Explain how the follow-up study could be said to be an improvement on the original study.
Practise AQA A Level Psychology Scientific processes with exam-style questions for A Level Psychology. 689 questions, matched to the AQA A Level Psychology (7182) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
