How to include the denominator or "n" on charts
When we present data, why is it important to include the denominator or “n”?
Knowing the “n” enables our audience to accurately interpret the data we present. The three main reasons for showing denominator values are:
- The denominator can indicate the scale on which we are working. Our audience will often ask, “When you say 60% of clients are receiving proper care, how many clients are we talking about?” Our audience wants to know if we are talking about 10 clients per month or 10,000.
- Variations in the denominator can help interpret indicator results. Sometimes a spike or drop in a denominator explains some of the variation in our indicators. For example, a health facility may be overwhelmed by an influx of refugees, causing the quality of care to decrease. Another example is that many services are expected to increase, such as services for people living with HIV being retained in care. With these indicators, the denominator should continue to increase as more people living with HIV are retained in care and their health improves. If not, there may be something wrong with the way the data are collected.
- When taking a sample from a population, the size of the sample (“n”) influences the statistical significance of the results. If we are using data from a sample rather than including data from all of the patient visits or other encounters, then the size (and variation) of the sample determine how confident we can be that our sampled indicator value reflects the true value for the entire population. For example, if we take a random sample of 20 women out of 100 delivering in a facility to see if their partograph was correctly completed and find that 50% (10/20) were, this doesn’t necessarily mean that 50 out of the 100 total women had correct partographs. However, if the sample was truly random, we can be reasonably sure that somewhere between 27 and 73 of the 100 women had correctly completed partographs.
Download the resource below to learn how to include the denominator ("n") on charts.