| Years | Regular Sample Hospitals | Total Sample Hospitals |
|---|---|---|
| 1988 | 758 | 759 |
| 1989 | 875 | 882 |
| 1990 | 861 | 871 |
| 1991 | 847 | 859 |
| 1992 | 838 | 856 |
| 1993 | 913 | |
| 1994 | 904 | |
| 1995 | 938 | |
| 1996 | 906 | |
| 1997 | 1,012 | |
| 1998 | 984 | |
| 1999 | 984 | |
| 2000 | 994 | |
| 2001 | 986 | |
| 2002 | 995 | |
| 2003 | 994 | |
| 2004 | 1,004 | |
| 2005 | 1,054 | |
| 2006 | 1,045 |