This deep dive covers Evaluating Your Investigation: Reliability, Validity, and Improvements 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 10 of 16 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.

🔎 Evaluating Your Investigation: Reliability, Validity, and Improvements

Evaluation is often worth the most marks on a fieldwork question and is the hardest skill to demonstrate. Students who score well at this level do three things: they identify a specific weakness, explain why it is a problem for the investigation, and suggest a realistic, targeted improvement.

Key Concepts: Reliability vs Validity

Concept	What It Means	How to Improve It
Reliability	Would you get the same results if you repeated the investigation? Reliable data can be reproduced.	Repeat each measurement 3 times and calculate the mean; use more sites; return to the same sites in different seasons
Validity	Does your method actually measure what you intended to measure? Are you controlling the right variables?	Use the same person to release the orange at every site (removes variation caused by different throwing styles); measure at the same time of day at every site; control the length of the float course
Accuracy	How close are your measurements to the true value?	Use a flow meter instead of the float method for velocity; calibrate equipment before use; ensure tape measures are not stretched or kinked
Representativeness	Does your sample reflect the full range of conditions you are investigating?	Increase sample size (more pebbles per site; more sites); use stratified sampling to cover upper, middle, and lower course

Specific Weaknesses to Mention in Exam Answers

Float method only measures surface velocity. The fastest water is near the surface; velocity at the bed is typically 20–30% slower due to friction. This means our velocity figures overestimate the mean velocity of the whole cross-section. To improve this, we could use a flow meter set at 0.6 times the depth (the standard depth for mean velocity measurement) at two or three points across the channel.

Only one visit to the river. River discharge and velocity vary enormously with weather and season — a river measured after a week of dry weather will behave very differently from the same river after two days of heavy rain. A single visit cannot tell us whether our results are typical or exceptional. To improve reliability, we could revisit the same sites in different seasons (autumn, spring) and compare results.

Small pebble sample (10 per site). With only 10 pebbles, one very large or very small pebble can significantly distort the mean. Increasing to 20–30 pebbles per site would produce a more stable, representative mean size and roundness.

Subjective roundness assessment. The Powers Roundness Scale requires visual judgement, which varies between students. Two people assessing the same pebble may assign different roundness values, introducing inconsistency. This could be reduced by having the same student assess all pebbles, or by photographing pebbles and having one person assess all photos after the fieldwork day.

Only 5 sites. With only 5 data points, a single anomaly at one site significantly distorts the overall pattern. Adding 3–4 more sites (especially in the middle course, which is often undersampled) would produce a clearer picture and reduce the influence of any single anomalous reading on the Spearman's rank value.

Evaluating Your Investigation: Reliability, Validity, and Improvements