Statistical tests are tools scientists use to spot important results – those rising above the randomness or “noise” in the universe. We use statistical tests in A-level biology, too. Even if a change in our data “looks” dramatic by eye, the test provides the unbiased reassurance to make our conclusions confidently.
Statistical tests work by setting a threshold (called the probability value level, p-value level or confidence level) used to spot significant changes from differences that could be explained by randomness in our measurements. Only data rising above this threshold gain the title “significant”.
But how do we know which statistical test to use?
Choosing statistical tests in A-level biology
Firstly, some good news – you don’t need to memorize any mathematical formulae! If you need them in the exam, they will be given to you. But you do need to know how and when use the tests. (And if you are with the OCR or Edexcel exam boards you may have to actually do some calculations.)
Which statistical test we use depends on what best suits your data. We have a choice of three different statistical tests in A-level biology:
Chi-squared test – used when looking at differences between frequencies (data that is counted) in different categories (known as discrete data).
Student’s t-test – used to look at differences between means (averages) of data involving measurements (like lengths, or times).
Spearman’s rank correlation coefficient test– used to look at the correlation between two variables in measured data.
Here is a diagram to help you choose:
Hopefully this helps with you choose between statistical tests in A-level biology exam questions! This blog is part of a larger study guide to A-level biology statistics (see below). I’ve also written about how to answer A-level biology evaluate questions, and application questions, but what about “Describe” and “explain” questions.
Good luck!
There’s much more help with statistical tests, p-values, significance etc. (and model answers to exam questions) in our shiny eBook “How to use statistical tests in A-level biology”, available in our shop. A purchase from our shop gives you a month’s free subscription to “ask an expert” – very useful for some exam practice 🙂
If you’d like to work through some A-level biology statistics questions, from exam boards like AQA, please get in touch with me at Woolton Tutors, and we can set up some online A-level biology tutoring sessions. If you have a few quick questions, have a look at our Ask an expert service.
Best wishes,
John
Dr John Ankers
Specialist online A-level biology tutor and academic wellbeing coach
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