2 added 589 characters in body; added 5 characters in body
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Choose the questions one by one as the user progresses through the survey rather than selecting them in advance.

***** edit

Assume that the survey is completed online via a website.

User logs in and opens survey

User opens first question.

system selects a question which has not been answered the required number of times yet

User fills in answer

User moves to next question

system selects a question which has not been answered the required number of times yet....

Etc

Each question is only selected as the user requests it. Thus you can apply a shorter timeout to 'user has opened a single question and left the browser open'. Vs 'user has registed to do a survey and hasn't got back to us yet'

Choose the questions one by one as the user progresses through the survey rather than selecting them in advance.

Choose the questions one by one as the user progresses through the survey rather than selecting them in advance.

***** edit

Assume that the survey is completed online via a website.

User logs in and opens survey

User opens first question.

system selects a question which has not been answered the required number of times yet

User fills in answer

User moves to next question

system selects a question which has not been answered the required number of times yet....

Etc

Each question is only selected as the user requests it. Thus you can apply a shorter timeout to 'user has opened a single question and left the browser open'. Vs 'user has registed to do a survey and hasn't got back to us yet'

1
source | link

Choose the questions one by one as the user progresses through the survey rather than selecting them in advance.