AQA A-level biology error bars and probability: revision notes and model answers

One page revision notes for AQA explaining the idea of error bars. I include model answers for a range of types of question and explanation of what p < 0.05 means. I list a couple of past paper questions which have good questions to practice from, all from the current specification.

AQA want you to say that differences are significant if error bars don’t overlap, even though in reality it’s more complicated than that. I clearly explain this and say that this idea shouldn’t be used if students go on to degree-level statistics.

Questions and mark schemes consulted in writing these notes included:

• significant difference: 74022 2020 2.4
• differences that are not significant: 74012 2019 1.2
• range error bars: 74023 2017 2.5
• no error bars: 74022 2020 7.2
• probability and chance: 74021 2019 4.4

Update, 2024: Following feedback from a student, added scale to clarify that the error bar shows mean ± SD. Clarified that the comments on probability/significance are when comparing means (so e.g. wouldn’t apply to the chi-squared test).