Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Year | Political Rights | Civil Liberties | Status | President |
| --- | --- | --- | --- | --- |
| 1972 | 6 | 6 | Not Free | Hamani Diori |
| 1973 | 6 | 6 | Not Free | Hamani Diori |
| 1974 | 7 | 6 | Not Free | Hamani Diori |
| 1975 | 7 | 6 | Not Free | Seyni Kountché |
| 1976 | 7 | 6 | Not Free | Seyni Kountché |
| 1977 | 7 | 6 | Not Free | Seyni Kountché |
| 1978 | 7 | 6 | Not Free | Seyni Kountché |
| 1979 | 7 | 6 | Not Free | Seyni Kountché |
| 1980 | 7 | 6 | Not Free | Seyni Kountché |
| 1981 | 7 | 6 | Not Free | Seyni Kountché |
| 1982 | 7 | 6 | Not Free | Seyni Kountché |
| 1983 | 7 | 6 | Not Free | Seyni Kountché |
| 1984 | 7 | 6 | Not Free | Seyni Kountché |
| 1985 | 7 | 6 | Not Free | Seyni Kountché |
| 1986 | 7 | 6 | Not Free | Seyni Kountché |
| 1987 | 7 | 6 | Not Free | Seyni Kountché |
| 1988 | 6 | 6 | Not Free | Ali Saibou |
| 1989 | 7 | 6 | Not Free | Ali Saibou |
| 1990 | 6 | 5 | Not Free | Ali Saibou |
| 1991 | 6 | 5 | Partly Free | Ali Saibou |
| 1992 | 5 | 4 | Partly Free | Ali Saibou |
| 1993 | 3 | 4 | Partly Free | Ali Saibou |
| 1994 | 3 | 5 | Partly Free | Mahamane Ousmane |
| 1995 | 3 | 5 | Partly Free | Mahamane Ousmane |
| 1996 | 7 | 5 | Not Free | Mahamane Ousmane |
| 1997 | 7 | 5 | Not Free | Ibrahim Baré Maïnassara |
| 1998 | 7 | 5 | Not Free | Ibrahim Baré Maïnassara |
| 1999 | 5 | 5 | Partly Free | Ibrahim Baré Maïnassara |
| 2000 | 4 | 4 | Partly Free | Mamadou Tandja |
| 2001 | 4 | 4 | Partly Free | Mamadou Tandja |
| 2002 | 4 | 4 | Partly Free | Mamadou Tandja |
| 2003 | 4 | 4 | Partly Free | Mamadou Tandja |
| 2004 | 3 | 3 | Partly Free | Mamadou Tandja |
| 2005 | 3 | 3 | Partly Free | Mamadou Tandja |
| 2006 | 3 | 3 | Partly Free | Mamadou Tandja |
| 2007 | 3 | 4 | Partly Free | Mamadou Tandja |
| 2008 | 3 | 4 | Partly Free | Mamadou Tandja |
| 2009 | 5 | 4 | Partly Free | Mamadou Tandja |
| 2010 | 5 | 4 | Partly Free | Mamadou Tandja |
| 2011 | 3 | 4 | Partly Free | Salou Djibo |
Question:
how long did it take for civil liberties to decrease below 6?
Answer:
18 years