"stratify on target and group by space works"
"group by space works with multiple observations within space unit"
"group by time works with multiple observations within space unit"
"group by space and time works with multiple observations within space unit"
"stratify on target and group by space works with multiple observations within space unit"
"group by space works with one polygon more than folds"
"group by space errors with one spatial unit less than folds"
"The number of folds is higher than the number of spatial units."
"group by time errors with one temporal unit less than folds"
"The number of folds is higher than the number of temporal units."

group by space works with one polygon more than folds