Takes a binary presence-absence matrix and returns the variance of the Stone and Roberts' (1990) C-score.

1 | ```
c_score_var(m = matrix(rbinom(100, 1, 0.5), nrow = 10))
``` |

`m` |
a binary presence-absence matrix in which rows are species and columns are sites. |

A large value of this variance implies that some species pairs in the matrix are strongly segregated (large C-score) and other species pairs are random or aggregated.

Returns the variance of the C-score calculated across all possible species pairs in the matrix.

The matrix-wide C-score is not calculated for missing species, so empty rows in the matrix do not affect the result. This index has not been thoroughly tested with real data sets.

Stone, L. and A. Roberts. 1990. The checkerboard score and species distributions. Oecologia 85: 74-79.

Stone, L. and A. Roberts. 1992. Competitive exclusion, or species aggregation? An aid in deciding. Oecologia 91: 419-424.

`c_score`

co-occurrence index.

1 | ```
varCScore <- c_score_var(m=matrix(rbinom(100,1,0.5),nrow=10))
``` |

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