This question already has an answer here:
I'm calculating Pearson's r for a set of dichotomous values.
For one item in my data set, all values are identical. Since the variance in y will be 0, I will ultimately end up with a division by 0.
I guess I have two questions:
Is it fair to say that the correlation coefficient is 0, or is it more valid to say that it cannot be calculated for this item?
Is manually checking for 0 variance and treating this as an exception the accepted best practice, or can the formula be modified to cater to this scenario?