The index in the DMP Reach Opportunities report shows the relative audience density of your users in comparison to all the users in the DMP universe for each 3rd party data provider rule.
An index of 100 for a certain rule means that the percentage of your total users in that rule is the same as the percentage for the entire population. An index of 200 suggests that you have twice the percentage of users in the rule than all the users in the DMP universe.
Say that Salesforce DMP universe has 1,000 total devices. 100 of those devices are in the 3rd party data provider rule "Ice Cream Lovers". That means 10% of the entire universe are "Ice Cream Lovers".
Now, say that you have 100 users total in your DMP instance. If 10 of these users are in the "Ice Cream Lovers" rule, that would be 10% of your users. The ratio of "Ice Cream Lovers", 10%, would be same for your account as it is for the whole DMP universe. As such, the Index would be 100 meaning your audience has the same distribution as the "average client".
If 20 of your users were "Ice Cream Lovers", that would be 20% and twice as much as the DMP universe. The Index would be 200. If only 5 of your users were "Ice Cream Lovers", that would be 5% and half as much as the DMP universe, resulting in an Index of 50.
By using this data, Publishers are able to identify which audiences are "strong" in comparison to other publishers. Your ad sales team could pitch high indexing segments by saying to potential advertisers, "If you are looking for Ice Cream Fans, you are more likely to find them on our websites than on any other Publisher's."
Marketers can use this report to discover what their audiences are interested in and try out new segments that they may have not thought about previously. Who knew their audience was highly indexed with Ice Cream Fans? Marketers can then adjust their advertisements accordingly.
To zoom into the chart, select a section of the chart
You can create a new segment comprised of 3rd party data by selecting data rule points and clicking Create Segment in the righthand panel.