Google Tag Manager and Optimizely

optimizely-gtm.html

<script>
    // Curry Optimizely optimizely.activateUniversalAnalytics() into GTM via window.optimizelyGTM
    (function() {
        window.gtmData = window.gtmData || [];
        window.optimizelyGTM = window.optimizelyGTM || {};
        var oldObj = window.GoogleAnalyticsObject;
        window.GoogleAnalyticsObject = 'gtmtmp';
        window.gtmtmp = function(set, dim, val) {
            window.optimizelyGTM[dim] = val;
        };
        try {
            window.optimizely = window.optimizely || [];
            window.optimizely.push("activateUniversalAnalytics");
        } catch (e) {} finally {
            window.GoogleAnalyticsObject = oldObj;
            window.gtmtmp = undefined;
            delete window.gtmtmp;
            window.gtmData.push({event: 'gtm.curriedPageview'});
        }

    })();
</script>

1. Paste this code into a GTM Tag on "all pages"
2. Change your default GTM UA Pageview tag to fire on the GTM trigger gtm.curriedPageview
3. Create 3-5 Dimensions in the UA Admin as Session or User Level Variables (e.g., AB Testing - {index} where index is the next number from 1-20 you're using)
4. Create 3-5 GTM variables as javascript variable -> optimizelyGTM.dimensionN (e.g., optimizelyGTM.dimension4, optimizelyGTM.dimension5, etc...)
5. You can now track each experiment back to UA using the Options -> Analytics Integrations -> Universal Analytics -> Dimension Index modal in optimizely.

References: https://help.optimizely.com/Integrate_Other_Platforms/Integrating_Optimizely_with_Google_Universal_Analytics