This comparison covers Sampling Strategies: Choosing the Right Approach within Physical Geography Fieldwork for GCSE Geography. Revise Physical Geography Fieldwork in Fieldwork for GCSE Geography with 13 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 7 of 16 in this topic. Use this comparison to connect the idea to the wider topic before moving on to questions and flashcards.
⚖️ Sampling Strategies: Choosing the Right Approach
A sampling strategy determines where and how often you collect data. Your sampling strategy must match your enquiry question — and you must be able to justify it in the exam. Using the wrong sampling strategy can lead to biased results that do not reliably test your hypothesis.
| Strategy | How It Works | Best For | Limitation |
|---|---|---|---|
| Systematic sampling | Data collected at regular intervals — e.g., every 100 m downstream along the river | Detecting downstream patterns and trends; comparing sites fairly | May miss important features if they happen to fall between sampling points (e.g., a major tributary at 150 m) |
| Random sampling | Sites chosen using random numbers (e.g., from a random number table or app); every point has an equal chance of being chosen | Pebble sampling within a site (eliminates selection bias when choosing individual pebbles) | May produce a cluster of points in one part of the study area while leaving gaps elsewhere; can miss important features |
| Stratified sampling | The study area is divided into zones (e.g., upper, middle, lower course); a proportional number of samples is taken from each zone | Ensuring all parts of the river are represented even if the zones are different lengths | More complex to design; requires prior knowledge of the zones; time-consuming |
| Opportunistic/pragmatic sampling | Sites chosen based on access, safety, and available time — "wherever we could get to safely" | Realistic when access is limited or some sites are dangerous | Introduces bias — results may reflect accessible rather than representative locations; difficult to justify in a rigorous enquiry |
For most GCSE river investigations: use systematic sampling for sites (e.g., every 100–200 m downstream, or at 5 specified points from source to mouth) combined with random sampling within each site for pebble collection. This is the combination most likely to earn full marks in an exam question about sampling justification.
How many sites? A minimum of 5 sites is needed to identify a trend with reasonable confidence. More sites (8–10) produce a more reliable picture but require more time. Your choice should be justified: "We used 7 sites to ensure the entire river from moorland source to urban lower course was sampled, allowing us to test the Bradshaw Model predictions across the full downstream gradient."
Practice questions for Physical Geography Fieldwork
A student drops an orange into a river and times how long it takes to travel 10 metres. Which variable are they measuring?
Describe how you would use the float method to measure river velocity at one site. Include how you would improve the reliability of your results.