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:
| Institution | Location | Founded | Type | Enrollment | Nickname | Joined |
| --- | --- | --- | --- | --- | --- | --- |
| Avila University | Kansas City, Missouri | 1916.0 | Private / Catholic | 1939.0 | Eagles | 2000 |
| Baker University | Baldwin City, Kansas | 1858.0 | Private/ Methodist | 4112.0 | Wildcats | 1971 |
| Benedictine College | Atchison, Kansas | 1858.0 | Private/Catholic | 2012.0 | Ravens | 1991 |
| Central Methodist University | Fayette, Missouri | 1854.0 | Private/Methodist | 4500.0 | Eagles | 1971 * |
| Culver–Stockton College | Canton, Missouri | 1853.0 | Private/ Disciples of Christ | 810.0 | Wildcats | 1980 |
| Evangel University | Springfield, Missouri | 1955.0 | Private/ Assemblies of God | 1911.0 | Crusaders | 1987 |
| Graceland University | Lamoni, Iowa | 1895.0 | Private/non-sectarian | 2444.0 | Yellowjackets | 1971 |
| MidAmerica Nazarene University | Olathe, Kansas | 1966.0 | Private/ Nazarene | 1743.0 | Pioneers | 1980 |
| Missouri Valley College | Marshall, Missouri | 1889.0 | Private/ Presbyterian | 1727.0 | Vikings | 1971 |
Question:
What is every year for joined with the Ravens nickname?
Answer:
1991.0