Table 1.

Summary of missing data categories

	Explainable logic (vs. random)	Identifiable pattern	Affects statistical inference	Action
Structurally Missing Data (SMD)	X			Exclude entry
Missing Completely At Random (MCAR)			X	Impute
Missing At Random (MAR)		X	X	Impute
Missing Not At Random (MNAR)		X	X	Impute

Rows correspond to different missing data scenarios; columns correspond to relevant characteristics. First column stands for the origin of the missing data (randomly generated or not). Second column states if a pattern of missing data can be recognized in the data set. Third column shows the impact on statistical inferences. The last column shows the action that needs to be taken to address the missing data problem