eVars are the primary custom variable used in Adobe Analytics. Understanding how these variables work can provide users with meaningful insights into the data they look at.
When data is sent to Adobe Analytics, the server call is translated into a single row of data with hundreds of columns. Two columns are dedicated to each eVar, one for direct data collection and the other for persisting values.
- The standard evarXX column contains data sent to Adobe from an image request.
- The post_evarXX column contains persistent data, which depends on the eVar's expiration and allocation.
Under almost all circumstances, the post_evar column is used in calculating reports.
Success events and eVars are frequently defined in different image requests. The post_evar column allows eVar values to tie themselves to events, showing data in reporting. Take the following visit for example:
- A visitor comes to your site and lands on the home page.
- They search for "cats" using your site's internal search. Your implementation sets eVar1 to internal search.
- They view a product, and proceed through the checkout process.
A simplified version of the raw data would look like the following:
- visitor_id is how Adobe ties hits to the same user. In actual raw data, the concatenated values of visid_high and visid_low determine visitor ID.
- pagename is what populates the Pages report.
- evar_1 is set on all image requests that explicitly define eVar1.
- post_evar_1 carries the previous value, dependent on the variable's allocation and expiration set in the admin console.
- event list contains all metric data. For this example, event1 is 'Searches', and the other events are standard shopping cart metrics. In actual raw data, event_list contains a comma-delimited set of numbers with a lookup table tying those numbers to a metric.
Adobe Analytics reporting tools (such as Analysis Workspace) work off this collected data. For example, if you pulled an Internal Search Terms report using Orders as the metric, the back end logic would be:
- Look through all event_list values, and pick out all the hits with 'purchase' in them.
- Out of those hits, display the post_evar1 value.
If the above example was the data set, pulling this data in Adobe Analytics would look like the following:
Since data sets typically do not consist of a single visit, there would be many line items. The number of orders tied to each unique eVar value would be displayed.
Since allocation and expiration determine what values persist, they are vital in getting the most value out of an analytics implementation. It is highly recommended to discuss how multiple values for an eVar are handled (allocation) and when eVars stop persisting data (expiration).
- By default, an eVar uses last allocation. New values overwrite persisted values.
- By default, an eVar uses an expiration of visit. Once a visit ends, values stop being copied in the post_evar column.
eVar allocation and expiration can be changed in the Admin Console under Report Suite Settings > Conversion > Conversion Variables.