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First teaching 2023

First exams 2025

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Evaluating COVID-19 Data: Skills (HL IB Biology)

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Naomi H

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Naomi H

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Evaluating COVID-19 Data

Calculating percentage difference

  • 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 space difference equals fraction numerator difference space between space two space values over denominator average space of space two space values end fraction space straight x space 100

Worked example

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 space 392 space minus space 1 space 584 space equals space 16 space 808

Step 2: Calculate the average of the two values

fraction numerator 18 space 392 space plus space 1 space 584 over denominator 2 end fraction space equals space 9 space 988

Step 3: Cubstitute numbers into the formula

Percentage space difference equals fraction numerator 16 space 808 over denominator 9 space 988 end fraction space straight x space 100

equals space 168.3 %

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

Calculating percentage change

  • 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 space change space equals space fraction numerator change over denominator original space value end fraction straight x space 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

Worked example

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

space 38 space 950 space minus space 18 space 392 space equals space 20 space 558

Step 2: Substitute numbers into the equation

Percentage space change space equals space fraction numerator 20 space 558 over denominator 38 space 950 end fraction straight x space 100

equals space 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

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    Naomi H

    Author: Naomi H

    Expertise: Biology

    Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.