Exam Connection

Level 1 (1 mark): "You could take more measurements."
Why only 1 mark: vague — does not say what measurements, how many, or why this improves reliability.

Level 2 (2 marks): "You could take three repeat velocity measurements at each site and calculate the mean. This would reduce the effect of random error caused by turbulence and inconsistent technique, making the data more reliable because individual readings are less likely to skew the result."
Why full marks: names a specific improvement, explains the mechanism, links it explicitly to reliability.

Level 1 (1–3 marks): "The investigation was mostly effective. We collected data from 5 sites which showed the pattern we expected. There were some problems with the weather."
Why only Level 1: describes what happened rather than evaluating quality; no reference to reliability, validity, or representativeness; no specific data values cited.

Level 2 (4–6 marks): "The investigation provided evidence to support the hypothesis — velocity generally increased downstream in line with the Bradshaw Model. However, Site 3 was an anomaly, possibly due to a waterfall increasing turbulence. The sample size of 5 sites was small and limits the reliability of conclusions. Repeating measurements would improve this."
Why Level 2: identifies pattern and anomaly with some explanation; notes a limitation with a basic improvement; but does not use quantitative evidence or address multiple evaluation dimensions.

Level 3 (7–8 marks): "The investigation largely supported the hypothesis: a Spearman's rank coefficient of r_s = +0.81 indicates a strong positive correlation between distance downstream and velocity, which is statistically significant at the 95% confidence level for n = 8 data pairs. Three limitations reduce the overall reliability and validity: first, the float method measures surface velocity only, which overestimates mean channel velocity by approximately 20% compared to a flow meter at 0.6 × depth — affecting validity. Second, all data was collected on one afternoon in November; discharge on that day may not represent typical conditions, reducing representativeness. Third, the sample of 8 sites, while sufficient for basic pattern identification, is at the minimum for reliable Spearman's rank — 12+ sites would increase statistical confidence. The anomaly at Site 4 (lower than expected velocity) is likely explained by the tributary junction at that point, which temporarily increases turbulence. To improve the investigation, I would use a flow meter rather than the float method, and extend the transect to 12 sites with data collected across three visits in different seasons."
Why Level 3: uses specific statistical evidence (r_s value, significance level, sample size); addresses all three evaluation dimensions; explains the anomaly geographically; proposes specific, justified improvements.