Dynamic Masking
Snap 9 incorporates the ability to apply answer masks which may be used to hide or display specified combinations of answer codes for single- and multi-response questions.
In last month’s worksheet we looked at a situation where some answers were never required for certain individual parts of a grid question and a static mask was applied. This worksheet looks at applying a dynamic mask, whereby the answer list for one question is masked by reference to the responses received to one or more previous questions.
The example uses four multi choice questions in an interviewer-led questionnaire. It is drawn from the snSupermarket survey which is preloaded on the Snap 9 Installation CD.
Step By Step
Step 1
The first question, Q1, is a multiple response question. The interviewer is told to not prompt for responses.
Step 2
Question 2 has the same code list as Q1. We want the interviewer to read out a list of the responses not mentioned in Q1.
Step 3
With Question 2 highlighted, click the 
Variable Properties button to bring up the properties of the selected question.
Step 4
Click in the entry for the Mask property and type ‘not Q1’. This will then exclude all responses previously made for Q1, from the list of possible answers for Q2.
Click OK to save your settings.
Step 5
In Question 3, we want to know their favourite store out of those selected in Q1 or Q2. Q3 has the same code list again but it is set as a single-response question.
Step 6
With Question 3 highlighted, click the Variable Properties button to bring up the properties of the selected question.
Step 7
Click in the entry for the Mask property and type ‘Q1 or Q2’. During an interview, this will only make available answers selected in Q1 or Q2.
Step 8
Another property in this window is 'Auto Answer'. It is used in conjunction with dynamic masking: if Auto answer is set to 'Yes' and if, during an interview, the question could be asked with only one possible answer, the question will be automatically removed and the single answer given. In this example, we would want Q3 to be automatically answered if the respondent was only aware of one supermarket at Q1 and Q2. Note in contrast we would want Q2 shown even if it had only one answer. A question that has no possible answers at all is never shown
Step 9
Click OK to save your settings.
Step 10
Question 4 is then asking for the respondent’s second favourite. We therefore need to add a mask to Q4 to further exclude the response given to Q3.
Step 11
With Question 4 highlighted, click the Variable Properties icon .
Step 12
Click in the entry for the Mask property and type ‘Q1 or Q2 and not Q3’. This will only display the code labels previously selected in Q1 or Q2, but will exclude the response given for Q3.
Step 13
We should also activate Auto answer for Q4: we would want for Q4 to auto answer if there was only one answer available for the respondent to choose a second favourite from.
Step 14
Test the masking by publishing the questionnaire with ‘preview only’ set in the Output section. Try completing the questionnaire with different combinations of answers at Q1, Q2 and Q3.