Presenting and analysing data at A2

Tables at A2

Everything from Unit 3 still applies: IV first, units in headings only, repeats and means, same decimal places.

The January 2024 report adds: 'tables should only have headings with units for raw data' when asked for raw data, and 'A heading RQ was not appropriate as it is a calculated value rather than raw data'. Be ready to correct significant figures or units in a table you are given.

Graphs matched to the analysis

• Two conditions: bar chart of means, y axis from zero, with standard deviation or range bars; test with a t-test.
• Many values of a continuous IV: scatter graph or line graph; test with Spearman's rank; or draw a line and find a gradient or constant.
• Counts in categories: bar chart; test with chi-squared.
• Growth over orders of magnitude: log scale.

The October 2023 mark scheme gave 2 marks for 'bar graph with labelled axes and a t-test for two light intensities, or a line or scatter graph and a correlation test for more than two'.

Describing analysis in a plan

A full answer says:

1. Calculate means (and rates) for each condition.

2. Calculate standard deviations.

3. Plot the graph (state the axes).

4. State the null hypothesis.

5. Name the test and say you will compare the calculated value with the critical value at p = 0.05 and reject or accept H₀.

Worked example

Describe how results comparing the respiration rate of diploid and tetraploid seeds (6 samples of each) should be presented and analysed.

1. Table: seed type, distance moved by fluid in each repeat / mm, rate / mm³ min⁻¹, mean.
2. Calculate mean and standard deviation of rate for each type.
3. Bar chart of mean rate with SD bars, y axis from zero.
4. H₀: no significant difference between mean respiration rates; t-test with 10 degrees of freedom; compare with 2.23 at p = 0.05.

Answer: Table of raw readings and rates, means and SDs, bar chart with error bars, t-test with H₀ and comparison at p = 0.05.

Check yourself

1. Which presentation suits mean zones of inhibition for two antibiotics, with repeats?
   • Bar chart of means with standard deviation bars
   • Scatter graph of each repeat
   • Log graph
   • Pie chart
   Show answer

   Bar chart of means with standard deviation bars. Two categories: bar chart with error bars.

2. Which presentation suits light intensity and percentage cover in 10 quadrats?
   • Bar chart of two means
   • Histogram
   • Scatter graph
   • Pie chart
   Show answer

   Scatter graph. Paired continuous data.

3. Which heading would be wrong in a table of raw data from a respirometer?
   • RQ
   • Distance moved by fluid / mm
   • Time / min
   • Mass of seeds / g
   Show answer

   RQ. RQ is calculated, not measured.

4. A plan compares two groups with 6 samples each using a t-test. How many degrees of freedom will be used?
   Show answer

   10. 6 + 6 - 2 = 10.

5. Which sentence best describes analysing results in a plan?
   • Look at the results and see if they are different
   • Calculate means and SDs, plot a graph, state H₀, use a named test and compare with the critical value at p = 0.05
   • Draw a graph if there is time
   • Use a statistical test
   Show answer

   Calculate means and SDs, plot a graph, state H₀, use a named test and compare with the critical value at p = 0.05. Specific steps score; 'use a statistical test' alone is vague.

6. Why must a bar chart's y axis start at zero?
   • So the error bars fit
   • So the x axis can be logarithmic
   • Bar charts never use zero
   • Otherwise the relative heights of the bars mislead the reader
   Show answer

   Otherwise the relative heights of the bars mislead the reader. The January 2024 report noted this.

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Sources

• Pearson Edexcel International Advanced Level in Biology specification (XBI11/YBI11, first teaching 2018): Unit 3, Unit 6 and Appendix 6 mathematical skills
• Pearson Examiners' Report WBI16/01, January 2024
• Pearson mark scheme WBI16/01, October 2023 (via Physics & Maths Tutor)

Last updated 8 November 2026. Spotted a mistake? Tell us.