Data Analysis and Interpretation
Core Concepts
Candidates must read tables and graphs accurately and compute basic statistics: mean (average), median (middle value), mode (most frequent), and range. Understand standard deviation as a measure of spread (large SD means widely scattered data), and error bars as indicators of variability or uncertainty. Know the difference between accuracy (closeness to true value) and precision (closeness of repeated measurements to each other). Recognize outliers, trends, and the meaning of a line of best fit. Understand that a statistically significant result is unlikely under the null hypothesis, but significance does not equal importance.
Traps
Common traps: confusing accuracy with precision; treating a single outlier as a trend; misreading axes that do not start at zero; and assuming a steep slope means a stronger relationship than a shallow one without checking units. Questions may present a mean without spread and expect you to notice that variability is unknown. Another trap is claiming a result is "proven" rather than "supported."
Rule of Thumb
Always check: What are the axes and units? Is the sample size shown? Are error bars present? Report both a central value and a spread.
Worked Example
Measurements: 10, 10, 11, 12, 47. The mean is 18, but the median is 11. The value 47 is an outlier that pulls the mean upward, so the median better represents typical data. Reporting "average = 18" without noting the outlier would mislead.