SARS, lay epidemiology, and fear

• Published in: The Lancet (British edition) Vol. 361; no. 9370; pp. 1739 - 1740
• Main Authors: Razum, Oliver, Becher, Heiko, Kapaun, Annette, Junghanss, Thomas
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 17-05-2003; Elsevier Limited
• Subjects: Data Interpretation, Statistical; Disease Outbreaks - statistics & numerical data; Epidemics; Epidemiology; Global Health; Humans; Models, Statistical; Severe acute respiratory syndrome; Severe Acute Respiratory Syndrome - epidemiology; Severe Acute Respiratory Syndrome - psychology; Hong Kong China; Asia; China; Germany
• ISSN: 0140-6736; 1474-547X
• DOI: 10.1016/S0140-6736(03)13335-1

A German newspaper2 fitted an exponential curve to the cumulative number of probable SARS cases (as reported by WHO3), forecasting a progressively steeper increase in case numbers. Under such conditions, almost everyone will become infected during the epidemic.4 However, a linear curve can be fitted to the same data, yielding an equally impressive R2 of 0.96, but predicting only 2410 cases 60 days later. [...]R2 statistics are invalid with cumulative data because the assumption that observations are independent is violated. Given the possibility of waning immunity, the data are also consistent with an emerging endemic situation in which a part of the population will be affected seasonally.4,5 Attempts to model the dynamics of an epidemic early on can lead to untenable conclusions, especially when based on worst-case scenarios such as a persistently high R0.