Because a cumulative frequency curve is nondecreasing, a concave-down curve looks like the left side of the ∩ symbol.Ī typical cumulative curve is somewhat S-shaped, as shown to the right.

In general, a concave-up curve looks like an upside-down U, like this: ∩. When the number of new cases is decreasing, the cumulative curve is 'concave down.'.The slope of the curve indicates the number of new cases. When the number of new cases is staying the same, the cumulative curve is linear.Because a cumulative frequency curve is nondecreasing, it looks like the right side of the ∪ symbol. When the number of new cases is increasing, the cumulative curve is 'concave up.' In general, a concave-up curve is U-shaped, like this: ∪.When the underlying quantity (new cases) is a count, the cumulative curve is technically a step function, but it is usually shown as a continuous curve by connecting each day's cumulative total.Ī cumulative curve for many days (more than 40) often looks smooth, so you can describe its shape by using the following descriptive terms: It either increases (when new cases are reported) or it stays the same (if no new cases are reported). When the underlying quantity is nonnegative (as for new cases of a disease), The numbers used in this article do not reflect any specific disease or outbreak. The shape of the cumulative curve indicates whether the daily number of cases is increasing, decreasing, or staying the same.įor this article, I created five examples that show the spread of a hypothetical disease. This article discusses how to read a cumulative frequency graph. However, the cumulative frequency graph is less familiar and is harder to interpret. The two graphs are related and actually contain the same information.

The graph is sometimes called a cumulative frequency graph.Īn example of each graph is shown above.

The total number of cases plotted against time.

The graph is sometimes called a frequency graph. This information is usually shown as a histogram or needle plot. The following two graphs appear frequently: During an outbreak of a disease, such as the coronavirus (COVID-19) pandemic, the media shows daily graphs that convey the spread of the disease.

Cumulative frequency histogram excel