Ignoring data values

There are several ways to drop, delete, remove or ignore data values.

 

1) Ignore elements or element combinations by modeling with an "M", Missing, model.

This method is most flexible, self-documenting, and easiest to undo. Before:

Models=

?,2,R ; Item 2 is on a rating scale (or partial credit)

?,?,D ; All other items are dichotomies

*

 

After:

1,3,M ; Ignore response by person 1 to item 3

4,?,M ; Ignore all responses by person 4

?,2,R ; Item 2 is on a rating scale (or partial credit)

?,?,D ; All other items are dichotomies

*

 

2) Delete the datum from the Data= file.

For single value references:

Before:

Data=

1,2,1

1,3,2 ; Datum to be deleted

1,4,3

 

After:

Data=

1,2,1

1,4,3

 

For multiple-value references:

Before:

Data=

1,2-4,1,2,3 ; Datum values of 2 is to be deleted

 

After:

Data=

1,2-4,1,,3 ; Blank data values are ignored

 

3) Comment out the datum value

For single value references:

Before:

Data=

1,2,1

1,3,2 ; Datum to be deleted

1,4,3

 

After:

Data=

1,2,1

; 1,3,2 ; this datum is ignored

1,4,3

 

For multiple-value references:

Before:

Data=

1,2-4,1,2,3 ; all 3 data values are to be deleted

 

After:

Data=

; 1,2-4,1,2,3 ; all 3 data values are ignored

 

4) To ignore all data values that include a specific element, delete or comment out that element number in the Labels= specification, e.g.,

Labels=

1, Students

1=George

; 2=Mary ; all elements referencing element 2 in facet 1 will be ignored

3=John

 

5) To ignore facet element references, BUT STILL VALIDATE ELEMENT REFERENCES, leave the facet control character blank.

Model=?,,?,D ; ignore facet element references for facet 2

Data=

4,5,6,1 ; analyzed as 4,0,6,1

 

6) To ignore an entire facet in the data, you can use the Entered= specification.

Entry = 1,0,2 ; the second facet in the data is to be ignored completely. No element number validation occurs.

Model=?,?,D ; model only the two active facets (1st and 3rd)

Data=

4,5,6,1 ; analyzed as 4,6,1

 

or use the "X" facet control character:

Model=?,X,?,D

 

7) To ignore every occurrence of particular response values in the data, you can use Missing=, e.g., data values "9" and "." are to be treated as missing data:

Missing = 9,. ; all 9's and periods are treated as missing.

 

8) To ignore every occurrence of particular response values for a particular Model= specification, e.g, value "3" is missing for rating scale (or partial credit) "Speed".

Model = ?, ?, Speed

*

Rating (or partial credit) scale = Speed, R6

-1=missing,,,3 ; recode 3 as -1, the missing value code.


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