Table 1.
Number of studies over year.
| Year | Studies, n |
| 2011 | 1 |
| 2012 | 1 |
| 2013 | 1 |
| 2014 | 7 |
| 2015 | 5 |
| 2016 | 12 |
| 2017 | 14 |
| 2018 | 8 |
| 2019 | 1 |
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.