Data quality in website traffic metrics: A comparison of 86 websites using two popular analytics services

Estimating website traffic is used in contexts such as business intelligence, competitive analysis, marketing, design, and research. However, the accuracy of popular traffic estimation services is a critical unanswered question. This research compares one year’s worth of average monthly analytics metrics data from Google Analytics with those from SimilarWeb for 86 websites of various sizes. The results show statistically significant differences between the two services for total visits, unique visitors, and bounce rates. Using Google Analytics as the baseline, SimilarWeb average values were 19.4% lower for total visits, 38.7% lower for unique visitors, and 25.2% higher for bounce rate. The website rankings between SimilarWeb and Google Analytics for all metrics are significantly correlated, especially for total visits and unique visitors. Finally, the differences between SimilarWeb and Google Analytics measures are systematic, so with Google Analytics metrics from a known site, one can reasonably estimate the Google Analytics metrics for similar sites based on the SimilarWeb values. The implications are that SimilarWeb provides conservative traffic estimates relative to those of Google Analytics and that the tools can be utilized in a complementary fashion in situations where direct site data is not available.