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How to convert a dataset in SAS to a .csv file so that it places
a dot "." in place of missing values.  
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Note that Proc Export can be used to create a .csv file but 
the missing data is not represented, simply 2 commas in a row are 
given.

To read data into Mplus, there must be some value given for a missing data,
it cannot read a blank.  It is fine if that value is "." but it can't be " " 
when using free format. 

The following simple use of ODS in SAS can be used to produce
a comma delimited file that has a "." placeholder for missings
since it simply copies the proc print (which shows "." by default)
into the designated file.

ods listing close;
ods results off;
ods csv file = "C:\mydirectory\datafile.csv";

proc print data = a noobs;
 run;

ods csv close;
ods results on;
ods listing;

Note in order to read this file into Mplus, it is still necessary to 
go in and delete the first row which has the variable names.
Mplus does not have the capability to read in variable names or even
to skip the first row.


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Missing data in Mplus 5.1 compared to previous versions

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The default in Mplus 5.1 is to do full information maximum
likelihood estimation in the presence of missing data (even for Exploratory
Factor analysis), whereas in earlier versions of the software the default
was LISTWISE deletion.

Note, if for some reason you desire to do LISTWISE deletion (for example
in order to compare to other software that only does listwise)

Then add the following statement in the DATA: section of the program

listwise = on;