Article No. 5 - Vol. 28, No. 4 - December 2009

Epidemiological Calendar 2010

The uses of surveillance data include the description and comparison of disease patterns using the person, place, and time variables. In particular, examples of the use of the time variable can be found in the earliest known epidemiological studies. For example, in a report on the 1847 influenza epidemic in London, William Farr presented data collected by week and easily calculated the excess of mortality due to influenza in different periods of the year. (1)

The discussion among statisticians from various disciplines on the use of specific time units seems to have been a constant at the beginning of the 20^th century. In May 1925, a document was presented to the British Royal Statistical Society, which argues for the first time that a period of time shorter than the calendar month (the week) is necessary as a “principle of division” of the year for purposes of vital statistics analysis. (2)

Today, there is an international consensus about the use of a standard time period to group deaths or other epidemiological events. This period is generally the week and is known as the epidemiological week. The division of the 365 days of the year in 52 epidemiological weeks is known as the epidemiological calendar. It is a way to standardize the time variable for the purpose of epidemiological surveillance.

The importance of this division and above all of the use of the epidemiological week relies on the fact that it allows for the comparison of epidemiological events that occurred in a given year or period of a year, with that of previous years. It also facilitates the comparison between countries.

Epidemiological weeks start on a Sunday and end on a Saturday; The first epidemiological week of the year ends, by definition, on the first Saturday of January, as long as it falls at least four days into the month, even if it means that this first week starts in December.

The 2010 Epidemiological Calendar begins on 3 January 2010. To illustrate the previous point, the following correspond to the first epidemiological weeks of a few consecutive years:

2005 January 2 – January 8, 2005

2006 January 1 – January 7, 2006

2007 December 31, 2006 – January 6, 2007

2008 December 30, 2007 – January 5, 2008

2009 January 4 – January 10, 2009

2010 January 3 – January 9, 2010

References

(1) Langmuir AD. William Farr: Founder of Modern Concepts of Surveillance. International Journal of Epidemiology 1976; 5(1):13-18

(2) Watkins H. Time counts: the story of the calendar. New York, Philosophical Library. 1954