Predictions for activity will be evaluated using the correlation coefficient \\(R^2\\), averaged over the 15 data sets.
$$ R^2 = \frac{1}{15}\sum_{s=1}^{15} r^2_s $$
where
$$ r^2_s =\frac{ [\sum_{i=1}^{N_s} (x_i-\bar x)(y_i-\bar y) ]^2}{ \sum_{i=1}^{N_s} (x_i-\bar x)^2 \sum_{i=1}^{N_s}(y_i-\bar y)^2  }$$
where \\(x\\) is the known activity, \\(\bar x\\) is the mean of the known activity, \\(y\\) is the predicted activity, \\(\bar y\\) is the mean of the predicted activity, and \\(N_s\\) is the number of molecules in data set \\(s\\).
Sample code has been provided to calculate r-squared.