International A Level Biology / Cardiovascular health and risk
Reading illness and mortality data revision notes
Edexcel International A Level Biology (YBI11), chapter 3: Cardiovascular health and risk, specification point 1.15, 1.18. Free lesson.
Watch the video lesson · International A Level Biology past papers
Illness and mortality data can show how disease rates change and whether factors are linked. Comparing rates, describing patterns and checking evidence carefully helps you avoid misleading conclusions.
Why compare rates rather than totals?
Mortality means death. A town with more deaths may simply have a larger population, so raw totals do not show which town has the higher death rate. A rate per 100 000 estimates how many deaths there would be in a group of 100 000 people. Use the same unit as the table or graph: deaths per 100 000 people. Compare the rates, not just the numbers of deaths.
How to describe a graph trend
Start with the overall pattern, then support it with figures from the graph and their units. Avoid listing every point. In the example, CHD death rates fall for both men and women. Women have lower rates than men throughout. The fall is steep at first, then levels off. Men: 400 deaths per 100 000 in 1990, falling to 130 per 100 000 in 2020. Mention a change in the shape of the trend, such as the line levelling off.
How to calculate percentage change
Percentage change compares a new value with the original value. A negative answer means the value has fallen. To compare groups, calculate each percentage change using its own original value.
How to recognise conflicting evidence
A positive correlation means that as one quantity rises, the other tends to rise too. But evidence that does not fit the pattern can show that the relationship is not the whole explanation. Country averages do not show what happens to every individual, and other factors or differences in recording deaths may affect the data. Countries A to E show CHD death rates rising as mean blood cholesterol rises. For example, A has 4.6 mmol dm⁻³ and 70 deaths per 100 000, while E has 6.0 mmol dm⁻³ and 240 deaths per 100 000. Country F does not fit: its mean cholesterol is 6.1 mmol dm⁻³, but its death…
What overlapping error bars mean
Error bars show the spread of data around each mean. If they overlap, the difference between the means could be due to chance, so it may not be statistically significant. This is about significance, not whether the data are reliable. Do not describe overlapping error bars as proof that data are unreliable.