Counting the number, percentage and types of cases
In order to count the number of cases of a particular disease or disorder, you need to be able to decide if a person really has that condition or not. You make your diagnosis based on criteria given in a case definition, i.e. a set of standard descriptions of the disease.
To calculate the percentage of cases that are due to a particular disease or disorder, you divide the number of cases of that condition (e.g. malaria) by the total number of cases of all diseases and disorders combined, and multiply the result by 100.
For example, there were four cases of malaria in the three days covered by the data in the table below, and 18 cases in total of all diseases or disorders. The percentage of malaria cases is therefore:
4 ÷ 18 × 100 = 22.2%.
So 22.2% of all cases seen in those three days in your health facility were due to malaria.
Use the table below to answer the following question. What is the highest ranking (i.e. most common) disease/disorder among people attending this health facility during the three days of data collection, and what is the second most common diagnosis?
List of causes of disease/disorder seen at one health facility during three days, ranked in order of magnitude
| Disease/disorder | Number of cases | Percent of total cases |
|---|---|---|
| Malaria | 4 | 22.2% (4/18) |
| Pneumonia | 3 | 13.6% (3/18) |
| Measles | 2 | 11.1% (2/18) |
| Injury (laceration, fracture) | 2 | 11.1% (2/18) |
| Meningitis | 2 | 11.1% (2/18) |
| Diarrhoea | 2 | 11.1% (2/18) |
| Tuberculosis | 1 | 5.5% (1/18) |
| Polio | 1 | 5.5% (1/18) |
| Abortion | 1 | 5.5% (1/18) |