Levin College of Law
It is important to always confirm that case law is still good law. In other words, you must make sure that the court decision has not been overruled or otherwise limited directly or indirectly. You use a CITATOR to determine if a decision remains valid and the extent to which it may have been criticized, distinguished, followed, explained, etc.
Shepard's is the citator tool in Lexis Advance and Nexis Uni. A case may be marked with one of the following signals.
The Shepard's signal appears in the upper left corner, next to the case name, and a Shepard's preview box appears to the right of the case in Lexis+:
Click on the Shepard's signal or the "Shepardize® document" button (below the Shepard's Preview) to get the full Shepard's Report, which looks like this:
KeyCite is the citator tool in Westlaw. Here is how it works:
Here is an example of a Florida state court case with a yellow KeyCite flag:
Click on the KeyCite flag to access additional KeyCite information. If the KeyCite symbol is a yellow or red flag, clicking on the flag will pull up all Negative Treatment from subsequent authorities, which looks like this:
For even more information about the subsequent treatment of your case, click on the Citing References tab at the top of the page. This will show all of the subsequent cases (as well as statutes and secondary sources, if any) that have cited to your case, whether negative, positive or neutral. 
In Fastcase, you can evaluate the precedential value of a case using the Authority Check tool. The Authority Check report for a case will show you later cases that have cited your case. Authority Check uses algorithms--which it calls Bad Law Bot--to find negative citation history of a case. Bad Law Bot will place a red flag next to a case when it finds negative treatment of that case.
