Some businesses install two or more analytics tools - it is possible to have a Google Analytics tool with Piwik or Woopra on the same site. Or have Adobe Analytics and Google Analytics on the same page. Many large organizations run both Adobe and Google - usually with Google at the onset of an analytics project, with Adobe considered for its ability to manage complex campaigns. Or WebTrends or Google Premium.... I think you get the point.
But not every result from a measurement tool will be exactly the same. The number count on Piwik may differ from that of a Google Analytics reports.
So what is the benefit of having dual tools on a site? The best answer lies in comparing data for general trends that appear on both tool. Given the same referral traffic and online conditions, a general increase in one can be similar in another. That can be useful to vet if conditions, such as a campaign effect, are indeed an influence on a result.
In this instance you are comparing precision across measurement tools. Precision in scientific terms is about repeatability - how well your results can be duplicated.
This perspective differs from that for accuracy. Accuracy is defined as a quality or state of being correct or precise; nearness to what should be in place. Given that there may be subtle differences in how solutions measure, you will have a difficult time reconciling different numbers. High data volume and data imperfection impair accuracy. Analytic solutions are not all the same, so there an be some accuracy discrepancy between solutions. How one measures the sources for a bounce rate may be different from another. You or your team can even waste time examining why a difference exists within a given time period between two solutions. Indeed using one solution can eliminate confusing decisions about trends in a set of data. It is ultimately the ideal arrangement for an analytic solution.
But for instances in direction regarding data accuracy,multiple solutions on a site can have a beneficial diagnostic effect for organizing potential reporting issues.
