Category: General  /  Created: 11/03/2015 14:53:07

What is missing data and types of missing data?

 

What is Missing data:

Information not available for a subject (or case) about whom other information is available. Missing data often occurs when a respondent fails to answer one or more questions in a survey.

Type of missing data:

1)       MCAR (missing completely at random)

       Classification of missing data applicable when missing values of Y are not present on X.

       When missing data are MCAR, observed values of Y are truly random sample of all Y values, with no underlying process that lends bias to the observed data.

2)       MAR (missing at random)

       Classification of missing data applicable when missing values of Y depends on X, but not on Y.

 

       When Missing data are MAR, observed data for Y are true random sample for the X values in the sample, but not a random sample of all Y values to missing values of X.