This help page describes how eVars work as a dimension. For information on how to implement eVars, see eVars in the Implement user guide.
eVars are custom variables that you can use however you'd like. If you have a solution design document , most dimensions specific to your organization end up as eVars. By default, eVars persist beyond the hit they are set on. You can customize their expiration and allocation under Conversion variables in Report suite settings.
The number of available eVars depends on your contract with Adobe. Up to 250 eVars are available if your contract with Adobe supports it.
Populate eVars with data
Each eVar collects data from the v1 in image requests. For example, the v1 query string parameter collects data for eVar1, while the v222 query string parameter collects data for eVar222.
Since eVars contain custom strings in your implementation, your organization determines what the dimension values are for each eVar. Make sure you record the purpose of each eVar and typical dimension values in a solution design document .
How eVars work
When you send data to Adobe Analytics, data collection servers translate the hit 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.
- A standard column contains data sent to Adobe from the image request.
- A "post" column contains persistent data, which depends on the eVar's expiration and allocation.
Under almost all circumstances, the post_evar column is used in reports.
How eVars tie to metrics
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 arrives to your site on your home page.
- They search for "cats" using your site's internal search. Your implementation uses eVar1 for internal search.
- They view a product, and proceed through the checkout process.
A simplified version of the raw data would look similar to the following:
- The visitor_id column ties hits to the same visitor. In actual raw data, the concatenated values of visid_high and visid_low determine visitor ID.
- The pagename column populates the Pages dimension.
- The evar column determines the hits when eVar1 was explicitly set.
- The post_evar1 carries the previous value, dependent on the variable's allocation and expiration set under report suite settings.
- The event_list column 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.
Translating data collection to reporting
Tools in Adobe Analytics, such as Analysis Workspace, work off of this collected data. For example, if you pulled a report using eVar1 as the dimension and Orders as the metric, you would see a report similar to the following:
Internal search term (eVar1)
Analysis Workspace pulls this report using the following logic:
- 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.
The importance of allocation and expiration
Since allocation and expiration determine what values persist, they are vital in getting the most value out of an analytics implementation. Adobe highly recommends that you discuss within your organization how multiple values for each 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 copying over from row to row in the post_evar column.
You can change eVar allocation and expiration under Conversion variables in Report suite settings.
Value of eVars over props
Adobe recommends using eVars in most cases, supported through the following:
- eVars have a 255-byte limit in reports. Props have a 100-byte limit.
- Props by default do not persist beyond the hit they are set. eVars have custom expiration, allowing you to determine when an eVar no longer gets credit for a subsequent event. However, if you use report time processing , both props and eVars can use a custom attribution model.
- Adobe supports up to 250 eVars, and only 75 props.
See prop for more comparisons between props and eVars.