observed: Input to be checked. Should be a numeric vector with the observed values of size n.
lower: Input to be checked. Should be a numeric vector of size n that holds the predicted value for the lower bounds of the prediction intervals.
upper: Input to be checked. Should be a numeric vector of size n that holds the predicted value for the upper bounds of the prediction intervals.
interval_range: Input to be checked. Should be a vector of size n that denotes the interval range in percent. E.g. a value of 50 denotes a (25%, 75%) prediction interval.
Returns
Returns TRUE if the check was successful and a string with an error message otherwise.