One very simple example of MECE groupings is basic survey demographic information, such as age groups. Every respondent fits into one and only one these buckets
How old are you (in years)?
When writing survey questions and answers, it’s important for answer choices to be as MECE as possible in order to provide the most valid results. For example, if a respondent feels that two options from a single-select multiple choice question are correct for her (because they are not mutually exclusive) she will only be able to choose one, either at random or influenced by some kind of bias, such as whichever one is closer to the top