The index in Reach Opportunities reflects how your user population compares to the entire population for each 3rd party data rule. The index shows the relative audience density of your account's users who belong to each rule. Adding a rule with a high index to a segment can help increase the population of that segment.
For example, an index of 100 suggests that the percentage of your users in that data provider rule is the same as the percentage of the entire population in this rule. An index of 200 suggests that you have twice the percentage of users in this segment than the entire population in this data provider rule.
You can view the indices and overlaps of an individual data provider by unselecting the data providers on the X-axis of the chart that you do not want to see.
Results depict the index over the last 30 days and are computed weekly for all enabled 3rd party data providers. The chart and export show the top 500 rules by overlap volume no matter what providers are selected on the X-axis.
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.