Let's look at data on deaths from the WHO covid-19 dashboard for 31st May 2020. The WHO dashboard has two options for statistics - total numbers which is shown in the left column and numbers per 1,000,000 population shown in the right column.
Five out of the ten countries in the column on the left column do not appear in the right column. The United States, the country with the most deaths overall, did not make it to the top 10 in deaths per 1,000,000 population. It is ranked 12 with 307 deaths per 1,000,000 population. Rather, San Marino which has recorded 42 deaths in total is leading the list of countries with deaths per 1 million population.
This illustrates why it is important to also standardize absolute numbers when reporting statistics. While the total death toll numbers are informative by themselves, standardized figures allow us to compare the impact on the population across different countries better than absolute numbers.
Population size varies by country and the impact of certain outcomes will vary by population size - for instance, a death toll of 100 in a population of a 200 (50%) is far more devastating than a death toll of 100 in a population of 10000 (1%). San Marino's population is estimated to be 33,000 compared to the United States estimated 322,180,000 population (WHO 2016 est.).
Belgium, which is the country with the second most deaths per 1 million population, and appears on both lists has recorded 9,467 deaths in an estimated population of 11,585,681. We can compare Belgium to Mexico which has reported 312 more deaths than Belgium. Mexico however does not appear in the top 10 countries for deaths per 1,000,000 because their estimated population of 127,540,000 is over ten times the population size of Belgium.
Now that we have discussed why standardizing is useful, the next question is how to standardize total figures. This is the formula that yields the rate per 1,000,000 population:
If we apply this formula to number of deaths, the statistic that is generated simply tells us what the number of deaths would be if the population size was 1,000,000. It means that if the population of the U.S.A and San Marino were both 1 million people then the covid-19 deaths reported would be 307 and 1,235 respectively.
That is simple standardization and it allows us to better compare what is happening in different populations.