Question: The data I am using from WHO on confirmed cases of malaria have some large differences in some years e.g. in 2008 it is 4508 and 2009 it is 211, whilst the rest of the data is in the millions (from 2000 to 2003 it is lower too). What is your opinion on why the data is so different? What would be the reasons and would you use such data in a statistical analysis or exclude them? Thank you (the articles you send are very useful too, I appreciate it).

Alena Pance answered on 1 Jun 2020:

Hi Sophia,
It depends on what is the data in question. Whether it refers to ‘malaria’ or to a specific species or whether it is world-wide or specific to a continent or a country.
There are 5 species of Plasmodium parasites that cause malaria: Plasmodium falciparum, Plasmodium vivax, Plasmodium malarie, Plasmodium ovale and Plasmodium knowlesi. The first 2 are the most common though their prevalence does not overlap. P. vivax and P. ovale can form hypnozoites in the liver that cause relapses of the disease and are difficult to eliminate. P. knowlesi has a short live cycle so the disease is very quick. But the most important and deadly is P. falciparum, that is wide-spread in Africa and kills in the range of half a million to a million children every year. Because the numbers in Africa are so frighteningly high, they dominate the world statistics in a way, and the difference from year to year isn’t that great.
Overall, there was a big decrease in malaria mortality and morbidity world-wide between 2000 and 2014, mainly brought about by the use of insecticidal mosquito nets and drug combination therapies, but since 2014 the progress in the control of the disease has flattened with fluctuations from year to year. Many of the fluctuations are due to lack of continuity in the control measures and activities, political and economic instability.
That’s more or less the picture world-wide in the last two decades. Sometimes the WHO pages are difficult to follow and you need to make sure you are looking at the right one.

I hope this helps,
Best wishes
Alena