How many (what percentage) of 'unengaged' respondents would you allow in your respondents database and what criteria would you employ in order to make e decision to eliminate/keep?
With respect to Likert scales, there are times, especially in lengthy self-reported questionnaires, when respondents provide 'linear' answers, i.e., they give, constantly, the same rating to all questions, regardless if the questions are reversed or not.
Some call this type of respondents 'unengaged' respondents. This, is rather a 'friendly' term, since there can be also malicious intent in providing, but this is another discussion. However we call them, the first direct effect on the data is reduced variability.
There may be other effects as well (feel free to list them based on your experience or knowledge), which can affect the relations between the constructs and the final inferences.
Thus, how do you proceed in these situations and what criteria do you base your decision on (supporting arguments are welcome and references to written texts are especially appreciated)?
(Edit): I realised that the original question my induce some confusion. This is not a case that require substitution (although, in general terms, it may be). Please consider that all cases are complete (all respondents answered each item). The problem lies within the pattern of responses. Some respond in straight line, hence the name 'straightlined' answers, others in various patterns (zig zagging, for instance), hence the name "patterned". While for scales which include reversed items, some cases (for instance, 'straightlined") can be easily spotted, for scales without reverse items, this is harder to to. However, the question pertains both situations (scales with and without reversed items).
Another particularity of the question is that I am less interested in "how to identify" this cases (methods) and much more in "what to do"/"how to deal" with them, i.e., what criteria or rules of thumbs or best practices to consider.
Responses including references to academic papers or discussions are much appreciated!