Evaluating COVID-19 Data: Skills | HL IB Biology Revision Notes 2025

Evaluating COVID-19 Data

A percentage difference calculation allows comparison of two directly comparable values that occur at the same time, e.g. the number of COVID-19 cases in two different countries at the same point in time
- Directly comparable values are values that mean the same thing, i.e. the number of COVID-19 cases and the number of COVID-19 deaths are two different types of value; they are not directly comparable
Percentage difference is calculated by dividing the difference between two values by the average of the two values
The resulting value is expressed as a percentage

$Percentage difference = \frac{difference between two values}{average of two values} x 100$

In mid-July 2023, Europe had 18 392 confirmed cases of COVID-19, while South-East Asia had 1 584 confirmed cases.

Calculate the percentage difference between the number of confirmed cases in Europe and South-East Asia

Step 1: Calculate the difference between the two values

$18 392 - 1 584 = 16 808$

Step 2: Calculate the average of the two values

$\frac{18 392 + 1 584}{2} = 9 988$

Step 3: Cubstitute numbers into the formula

$Percentage difference = \frac{16 808}{9 988} x 100$

$= 168.3$ %

There was 168.3 % difference between the number of confirmed cases in Europe and South-East Asia in mid-July 2023

A percentage change calculation allows comparison of two values from the same data set at different times, i.e. how a factor has changed over time
Percentage change is calculated by dividing the difference between an old and a new value, divided by the old value
The resulting value is also expressed as a percentage

$Percentage change = \frac{change}{original value} x 100$

If the original number is larger, then the change will be a percentage decrease, and if the original number is smaller then the change will be a percentage increase

In mid-June 2023, Europe had 38 950 confirmed cases of COVID-19, while in mid-July 2023, it had 18 392 cases.

Calculate the percentage change in COVID-19 cases in Europe between June and July 2023.

Step 1: Calculate the change in the number of cases

$38 950 - 18 392 = 20 558$

Step 2: Substitute numbers into the equation

$Percentage change = \frac{20 558}{38 950} x 100$

$= 52.8$ %

There has been a percentage change of 52.8 % in the number of European COVID-19 cases between June and July 2023

As the original value was larger than the new value, this can be represented as a negative number (-52.8 %) or described as a percentage decrease