Harvard Law School’s Caselaw Access Project, which last year completed a massive project to digitize all U.S. case law, this week released a tool called Historical Trends that allows a user to visually graph the frequency of words and phrases in those cases over time.
The tool is similar in function to the Google Books Ngram Viewer, which allows users to graph the frequency with which phrases have appeared in a corpus of books over time.
The Historical Trends tool can be used to search for phrases of up to three words and to compare multiple phrases. It also allows wildcard searching. Users can limit searches to specific jurisdictions. Results can be shown as a graph over time or in a table view.
Once you enter a query and generate a graph, you can click anywhere on the graph to create a list of “example cases” that show the use of the phrase within that time span. From the example cases, you can then conduct a search for the phrase in the full collection.
Last October, CAP completed a three-year project to digitize all U.S. case law, covering some 6.4 million cases dating back to 1658. The Historical Trends tool spans the years 1800 to 2018.
The tool can be used to chart usage of a single word, such as abortion. As you can see below, frequency of this word peaked in the years 2005-2013.
A search for the phrase “bear arms” produces an interesting result. The phrase occurred with greater frequency in the years prior to 1875, then fell off, and then fell to even greater frequency in the years 2009-2017.
Adam Ziegler, director of the Library Innovation Lab at Harvard that oversees the Caselaw Access Project, suggested some searches that show the range of the tool.
