Would 25 multiple choice questions be enough to detect random answering with certainty? Surely many combinations come up way more often than others when answered truthfully.
After that, some questions supposed to be perfectly correlated with previous are added. These should, however, use different words or concepts altogether, to avoid detection. These questions are meant to establish consistency, and would pick up on randomness
25 strikes me as too few to get into that kind of verification. I seem to remember serious personality tests to usually contain in the range of 100 to 200 questions.
How you ask a question can perturb the answer. If an axiom is that you're determining static elements of personality, then you'd need to ask about the same facets in different ways to avoid skewing the analysis.
"I am quick to react?"
vs
"I take time before reacting to make a measured response"
Both a priori sound positive, so people will tend to "somewhat agree" (as the answer format of these things goes), but they are seemingly antithetical.
Of course they're not really antithetical they're just shallow questions that aren't really going to discern much of your personality. People can react quickly/slowly according to the needs of a situation. Maybe the value is in measuring perceptions of one-another, despite the ease with which we are misguided.