missing data

Question 1

missing completely at random (MCAR)

Answer 1

genuine random missingness
missingness on y is not related to y or any other variable in the model

Question 2

missing at random (MAR)

Answer 2

when the probability of missing data on variable Y is related to other variables within the model, but not Y itself
there is no way to confirm this because we have no knowledge about the missing data

Question 3

missing not at random (MNAR)

Answer 3

when the probability of missingness on y is related to the values of y itself
there is no way to confirm this because we have no knowledge about the missing data