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3.6.12Additional lessons

Evaluating COVID-19 Data: Skills — IB Biology SL Revision Notes & Topical Questions

5 min read 6 parts Lesson 81 of 142

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Part 1 of 6Percentage Difference

3.6.12 Evaluating COVID-19 Data: Skills

Percentage difference compares two values at one time.

1
Use percentage difference to compare two directly comparable values measured at the same time, such as cases in two regions in one week.
2
Subtract the smaller value from the larger to find the difference.
3
Find the mean of the two values by adding them and dividing by two.
4
Divide the difference by the mean and multiply by 100 to get the percentage difference.
5
Only compare like with like, so cases cannot be directly compared with deaths.

Part 2 of 6Percentage Change

Use
  • Percentage change compares one value measured at two different times, such as cases in June and in July.
Formula
  • Percentage change = (new value − original value) ÷ original value × 100.
Sign
  • A negative result is a decrease and a positive result is an increase.
Original value
  • The original value is always the denominator, which is different from percentage difference.
CalculationComparesDivide by
Percentage differenceTwo values at one timeMean of the two values
Percentage changeOne value at two timesOriginal value

Part 3 of 6Evaluating the Data

Evaluating the Data
Reporting
  • Cases depend on how many tests are carried out and how widely they are reported.
Population size
  • Raw numbers favour large countries, so rates per 100 000 people give a fairer comparison.
Time lag
  • Deaths and hospital admissions follow infections by days or weeks.
Source
  • Data from a recognised health organisation that is peer reviewed is more reliable than an unreferenced claim.
Graphs
  • Check scale, units and axis labels before drawing conclusions, as scales can exaggerate small changes.

Part 4 of 6Drawing Conclusions

1
Describe the trend using data with units.
2
Calculate a suitable statistic and state exactly what it shows.
3
Consider limitations such as testing differences.
4
Conclude cautiously, noting that correlation does not prove cause.

Part 5 of 6Worked Example

Question

  • In one week region X reported 5 200 cases and region Y reported 3 000.
  • Calculate the percentage difference.

  1. Difference = 5 200 − 3 000 = 2 200.
  2. Mean = (5 200 + 3 000) ÷ 2 = 4 100.
  3. Percentage difference = 2 200 ÷ 4 100 × 100 = 53.66...%.

Answer 53.7%

Part 6 of 6Exam Checklist & Tips

3.6.12 – Key Points for the Exam

  • Percentage difference The difference between two values divided by their mean, × 100.
  • Percentage change The change in a value divided by its original value, × 100.
  • Pandemic An outbreak that spreads across many countries.
  • Peer review Evaluation of research by independent experts before publication.

Common Mistakes

  • Dividing by the new value instead of the original value when calculating percentage change.
  • Comparing cases with deaths using percentage difference.
  • Comparing raw case numbers between countries of very different population sizes.
  • Ignoring the sign of the result, which shows an increase or decrease.

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