IFT Institut für Therapieforschung, München, Germany.
Int J Drug Policy. 2013 Jan;24(1):23-9. doi: 10.1016/j.drugpo.2012.05.002. Epub 2012 Jul 17.
Prevalence estimation of cannabis use is usually based on self-report data. Although there is evidence on the reliability of this data source, its cross-cultural validity is still a major concern. External objective criteria are needed for this purpose. In this study, cannabis-related search engine query data are used as an external criterion.
Data on cannabis use were taken from the 2007 European School Survey Project on Alcohol and Other Drugs (ESPAD). Provincial data came from three Italian nation-wide studies using the same methodology (2006-2008; ESPAD-Italia). Information on cannabis-related search engine query data was based on Google search volume indices (GSI). (1) Reliability analysis was conducted for GSI. (2) Latent measurement models of "true" cannabis prevalence were tested using perceived availability, web-based cannabis searches and self-reported prevalence as indicators. (3) Structure models were set up to test the influences of response tendencies and geographical position (latitude, longitude). In order to test the stability of the models, analyses were conducted on country level (Europe, US) and on provincial level in Italy.
Cannabis-related GSI were found to be highly reliable and constant over time. The overall measurement model was highly significant in both data sets. On country level, no significant effects of response bias indicators and geographical position on perceived availability, web-based cannabis searches and self-reported prevalence were found. On provincial level, latitude had a significant positive effect on availability indicating that perceived availability of cannabis in northern Italy was higher than expected from the other indicators.
Although GSI showed weaker associations with cannabis use than perceived availability, the findings underline the external validity and usefulness of search engine query data as external criteria. The findings suggest an acceptable relative comparability of national (provincial) prevalence estimates of cannabis use that are based on a common survey methodology. Search engine query data are a too weak indicator to base prevalence estimations on this source only, but in combination with other sources (waste water analysis, sales of cigarette paper) they may provide satisfactory estimates.
大麻使用的流行率估计通常基于自我报告数据。尽管有关于该数据源可靠性的证据，但它的跨文化有效性仍然是一个主要关注点。为此目的需要外部客观标准。在这项研究中，使用与大麻相关的搜索引擎查询数据作为外部标准。
大麻使用数据取自 2007 年欧洲学校酒精和其他毒品调查项目 (ESPAD)。省级数据来自三项使用相同方法的意大利全国性研究（2006-2008 年；ESPAD-Italia）。与大麻相关的搜索引擎查询数据的信息基于 Google 搜索量指数 (GSI)。（1）对 GSI 进行可靠性分析。（2）使用感知可及性、基于网络的大麻搜索和自我报告的流行率作为指标，测试“真实”大麻流行率的潜在测量模型。（3）建立结构模型以测试响应倾向和地理位置（纬度、经度）的影响。为了测试模型的稳定性，在国家层面（欧洲、美国）和意大利省级层面进行了分析。
与大麻相关的 GSI 被发现高度可靠且随时间保持稳定。两个数据集的整体测量模型均高度显著。在国家层面，没有发现响应偏差指标和地理位置对感知可及性、基于网络的大麻搜索和自我报告的流行率的显著影响。在省级层面，纬度对可及性有显著的正向影响，这表明意大利北部大麻的感知可及性高于其他指标所预期的水平。
尽管 GSI 与大麻使用的关联比感知可及性弱，但研究结果强调了搜索引擎查询数据作为外部标准的外部有效性和有用性。研究结果表明，基于共同调查方法的大麻使用国家（省级）流行率估计具有可接受的相对可比性。搜索引擎查询数据是一个较弱的指标，不能仅基于此来源进行流行率估计，但与其他来源（废水分析、卷烟纸销售）结合使用，可能会提供令人满意的估计。
