Hulth and Rydevik BMC Public Health 2011, 11:252 http://www.biomedcentral.com/1471-2458/11/252 cannot use the total number of queries for a particular week as a denominator for normalization, for we would lose the seasonal variation. For these reasons we investi- gated a large number of common search terms, to find one without any seasonal variation, which would reflect only the increased usage of the web site. We settled for herpes, depicted in Figure 3, a search term which gra- phically seemed to have little seasonal trend, but a total increase over time that could reflect the increased usage of the web site. In the current implementation of GET WELL, each submitted query is normalized. This is done by dividing the number of queries by the expected number of searches for that week. The expected number of queries is calculated by using a locally polynomial smoothing function [13] to estimate the increasing trend of queries on herpes. The parameters of the function are chosen in such a way that the resulting curve subjectively captures the non-linear increase. The resulting trend is shown in Figure 3 with a red, dashed line. Results User requested time series In Figure 4, we present an example of a time series graph produced by GET WELL for a user entered request. In the figure, time series for the last five years (at the point of request) are shown for two query terms related to the winter vomiting disease: vomit (green, continuous line) and diarrhoea (blue, large dashes). The Figure 3 Number of queries on “herpes” submitted to Vårdguiden.se. The number of queries on herpes submitted to the Vårdguiden search engine from June 2005 to December 2009, aggregated by week, together with the estimated trend curve (red, dashed line). Page 4 of 8 Figure 4 Queries submitted to Vårdguiden.se. Example of a graph produced in week 34, 2010 by GET WELL, with media hits. The graph shows the number of articles on winter vomiting disease in Swedish media (black, small dashes), and the normalized number of queries on diarrhoea (blue, larger dashes) and vomit (green continuous) submitted to Vårdguiden, from week 35, 2005 to week 34, 2010. Week 34 each year is marked with a dot. graph also shows the number of articles on winter vomiting disease in Swedish online media (black, small dashes). The past week is marked with a dot in the graph for all years, to facilitate comparisons over the years. In the figure, the output from GET WELL was translated to English. Search patterns from Vårdguiden versus Google For the purpose of evaluating analyses on data from a medical web site and from a general purpose search engine, we downloaded data for two selected query terms from Google Insights for Search [14]. We extracted the time series for the same two query terms from the Vårdguiden search data. The two terms were the Swed- ish equivalences to vomit and to influenza. For both queries we wanted to compare the search patterns obtained from the two web sites. The Google search was restricted to Sweden and the terms in Swedish. The data provided by Google contain the relative search volume, and are already normalized and scaled, while the Vårdguiden data are only normalized. The weeks are differently aggregated: the Vårdguiden data starts the weeks on Mondays, while Google starts the weeks on Sundays. Influenza The term influenza was chosen so that we could com- pare how the enormous interest in this infectious