I have a dataset with 101 observations and 402 columns (those columns comprise several multiple-item questionnaires). Among those 402 columns, 10 of them are categorical and the remaining are continuous. There are 82 observations without missing values, which means 18% of the entire sample (N=101) has one or more missing values. There are 14 missing patterns with 10 of them containing only one observation.

I would like to examine if the missing data mechanism is MCAR in this dataset. I have tried LittleMCAR ("BaylorEdPsych" package) and TestMCARNormality ("MissMech" package) to test for MCAR using RStudio (version 1.1.442). However, LittleMCAR only allows a maximum of 50 variables; TestMCARNormality did not work out either. The code for TestMCARNormality is shown as below:

## df[1:10] were excluded due to their class of categorical variables; del.lesscases was set to 1 because default for this parameter was 6, and if set to default it would have no missing pattern in the test.

TestMCARNormality(df[11:402], del.lesscases = 1)

After I ran this code, it showed the following error:

Error in solve.default(sigoo) : system is computationally singular: reciprocal condition number = 1.37693e-17

I wasn't sure why this happen and what it meant. I was wondering if anyone knows how I can address this issue and how I can test MCAR for my dataset. Thank you in advance for your time; sincerely appreciated!!

  • $\begingroup$ Although this is about R, I think the fundamental issue is statistical so I am voting to leave it open. $\endgroup$ – Peter Flom - Reinstate Monica Apr 4 '18 at 12:58
  • $\begingroup$ Thank you for keeping this open, Peter. While some literatures did encourage a test for MCAR for determining a proper approach for dealing with missing data, some other literatures did also indicate that multiple imputation can deal with both MCAR and MAR (Enders, 2010). In such a case, it seems that I can proceed to the phase of imputation regardless MCAR or MAR (except for MNAR). I just don't understand why a test of MCAR is critical if I were able to deal with missing data by multiple imputation. $\endgroup$ – adonies Apr 4 '18 at 16:29

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