What's the date/number listed to the right of each search result?
The value in the right column changes based upon the current sort.
For most results, it displays the last date in the time period field, the date on which the study was undertaken.
If you sort by "Most Cited in ICPSR Bibliography," it will display the number of related citations that ICPSR has found in its bibliographic searches.
The "Most Downloaded" sort will display the number of unique users who have downloaded this study in the last 90 days.
"Released/Updated" will display the date on which the study was last updated or the release date (whichever is later).
On the previous version of the site, this was the date on which ICPSR released/updated the data, but we changed that in April 2010, as the time period is more useful to researchers.