Evaluating COVID-19 Data: Skills (DP IB Biology: SL): Revision Note

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

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

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

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

• 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