Does sediment size change along a beach?
Compare particle size at three positions along a beach.
The method
At each position, measure 20 pebbles selected from a marked grid using randomly chosen coordinates.
| Position | Median (mm) | IQR (mm) |
|---|---|---|
| North | 18 | 32 |
| Middle | 15 | 26 |
| South | 12 | 19 |
Choose a presentation
A box plot can show median and spread if all five summary values are available. This table alone is not enough to draw a complete box plot.
Follow a limitation through the enquiry
- Limitation
- Only surface pebbles were sampled during one visit.
- Effect on the evidence
- The results describe surface material on that visit. Recent storms could make the pattern unrepresentative of other dates.
- A useful improvement
- Repeat the same sampling method on other suitable dates and record tide and recent weather.
Try it yourself
Explain why the proposed improvement would help this enquiry. Then identify something it would still not establish.
One possible answer
Repeat the same sampling method on other suitable dates and record tide and recent weather. This strengthens the evidence for the stated enquiry, but a small study still cannot represent every place or date.
Check your answer: did you address the question, use accurate evidence and explain the link?
Change the conditions
Imagine the same enquiry on another date or at another site. Which part of the method would you keep consistent? Explain why, using the enquiry aim.
What to look for
A useful answer identifies a specific measurement, sampling rule or time condition and explains how consistency makes the comparison fairer.