Because Covid-19 cases are reported nonuniformly throughout the week, many news outlets add a curve showing the 7-day average (red curve) of the daily new cases (vertical bars). Students in the EPS 109 “Computer Simulations in Earth and Planetary Science” class were asked to investigate why this curve appears to be below the daily case numbers when Covid-19 cases are rising (blue arrows) but above most cases when the cases numbers are falling (green arrows). This mismatch appears to be an artifact resulting the way the 7-day average is typically calculated. For November 23, the point on the red curve is derived by averaging the daily cases from November 17-23. If instead a symmetric average is taken from November 20-26, the resulting blue curve in the second diagram tracks the data much more closely. Why most news outlets prefer the asymmetric average remains unclear. Maybe it is simply because they prefer to assign an average for the day of reporting instead of waiting three additional days until the symmetric average becomes available.
Data from https://ourworldindata.org/coronavirus was used for this analysis.
EPS 109 is taught by Professor Burkhard Militzer.