I actually found that what I was looking is referred to as "Active Share".
According to ActiveShare.info:
Active Share is the percentage of fund holdings that is different from
the benchmark holdings...
Active Share is not a measure of skill but rather measures how
different the fund's holdings are relative to the holdings of the
particular benchmark considered...
Research has shown that as a group and over fairly long periods of
- funds with low Active Shares have tended to underperform their benchmarks net of costs
- funds with high Active Shares have tended to outperform their benchmarks net of costs, especially among funds that do not trade
frequently, among small cap funds and among funds that do not have
very large assets under management (see further the section 'Active
...The papers below, co-authored by Martijn Cremers,
provide further background and explanation. For more information on
his academic research on Active Share, see activeshare.nd.edu.
The website also offers a search tool to determine a given fund's active share versus the S&P 500.