Interpreting health data and risk perceptionEdexcel International A Level Biology: Revision notes
Section 1
Illness and mortality data
Morbidity is illness; mortality is death. Incidence is the number of new cases in a population in a given time; prevalence is the total number of cases at a point in time.
Because populations differ in size, compare rates, such as deaths per 100,000 people, not raw numbers:
rate per 100,000 = (number of cases ÷ population) × 100,000
Worked example: 900 deaths in a population of 3,000,000 is 900 ÷ 3,000,000 × 100,000 = 30 per 100,000. If the earlier rate was 50 per 100,000, the percentage change is (30 − 50) ÷ 50 × 100 = −40%.
Quote figures from the data and use rates, not numbers of cases, when populations differ in size.
Section 2
Correlation, causation and conflicting evidence
A correlation is a relationship between two variables. It does not prove causation, because a confounding variable (for example age or smoking) may affect both. Evidence for causation is stronger when:
- there is a known mechanism (e.g. LDL deposited in plaques)
- there is a dose-response relationship
- several studies in different populations give consistent results
- controlled trials show that changing the factor changes the outcome.
Conflicting evidence arises from differences in sample, sample size, method, control of confounding variables, and bias (for example funding source). Weigh the evidence from many studies, preferably peer-reviewed.
Never write that data "prove" a cause from a correlation. Say that they suggest or support a link, and name possible confounding variables.
Section 3
Evaluating study design
When you evaluate a study consider:
- Sample selection: it should be random and representative (age, gender, ethnicity) to avoid bias.
- Sample size: a larger sample reduces the effect of chance and anomalies.
- Validity: the study measures what it claims to measure; confounding variables are controlled; the data collection method is accurate (self-reported diets may not be).
- Reliability: similar results are obtained when the study is repeated.
- Duration and control groups for comparison.
Validity is about measuring the right thing; reliability is about repeatable results. Do not mix them up.
Section 4
Perceived and actual risk
Actual risk is calculated from data on incidence and mortality. Perceived risk is a person's judgement of how likely harm is. They often differ because:
- the media give most attention to rare, dramatic events
- people underestimate risks that are familiar or that they feel they control (diet, smoking) and overestimate involuntary or frightening ones
- personal experience, for example a relative with CVD, changes perception.
This matters because people may ignore real risks of common diseases such as CVD, so campaigns must communicate clear, accurate data.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Interpreting health data and risk perception
- A health authority publishes mortality data for a disease. In 2010 there were 1,200 deaths from the disease in a population of 2,400,000 people. In 2020 there were 900 deaths in a population of 3,000,000 people.Calculate the percentage change in the mortality rate between 2010 and 2020.2 marks
- A study of the link between a type of fast food and heart disease recruited 60 volunteers, all of whom were students at one university. The researchers asked the volunteers to record what they ate for one week and then measured their blood pressure.Suggest two changes to the sample that would allow the conclusions to be applied more confidently to the general population.2 marks
- A study followed 100,000 adults for 12 years. Of the 20,000 adults who ate fewer than two portions of fruit and vegetables each day, 800 developed cardiovascular disease (CVD). Of the 20,000 adults who ate five or more portions each day, 500 developed CVD. The remaining adults ate between two and five portions each day. The diets were recorded by the adults themselves in questionnaires.Calculate the percentage reduction in the incidence of CVD in the group eating five or more portions each day compared with the group eating fewer than two portions.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).