Questionnaires are certainly in vogue in mental health research. Often they are referred to in technical-sounding jargon, for example it is common to call a questionnaire an "instrument" or a "measurement tool."
There are good reasons to have well-standardized questionnaires. In research, it is useful if people across the world are all using a similar type of questionnaire, so that comparisons can be made more easily and clearly.
In psychotherapy or other mental health practice, there is evidence that obtaining regular feedback from patients or clients can be valuable to improve the quality of the therapy, and to prevent mistakes. One of the leaders in showing the importance of this is Michael Lambert, an esteemed psychologist and psychotherapy researcher from Brigham Young University. In a nutshell, his research shows us that problems can occur in psychotherapy without the therapist realizing it: the patient or client could be developing new symptoms, detaching or losing interest in the therapy, feeling upset or disappointed with the therapist, or even developing a life-threatening emergency, but the therapist may not know this, because it is not talked about or asked about in the session. This could be because the patient is inhibited to share this information, but it could also be simply because the problem was never inquired about. In therapy sessions, just like with any other interaction, one can follow a certain narrative pathway habitually, therefore missing things that could be quietly going wrong in the background.
So Lambert has developed a questionnaire called the OQ-45, which consists of 45 simple questions covering everything from mood, anxiety, relationship satisfaction, loneliness, drinking, family life, work life, cognition, and physical health. The idea is for patients or clients to fill in this questionnaire frequently, maybe even before every therapy appointment, so that no potential evolving problem area would be "missed." The questionnaire would only take a few minutes to fill out, and could be done in the waiting room before an appointment. Samples of the OQ-45 can be found in an internet search.
I believe that this type of questionnaire is useful. Certainly we have to respect Lambert's many years of research, to acknowledge that feedback of this type can improve therapy.
But the therapeutic benefit of this is not due to some special property of the questionnaire itself! And the therapeutic benefit does not require the sophisticated statistical analysis that is offered to purchasers of the questionnaire! The benefit of this is simply to do a review of symptoms regularly with patients or clients.
Questionnaires in psychology have become a business. For hundreds of dollars, one can sign up to receive copies of a questionnaire, scoring manuals, or perhaps an on-line entry and scoring package, which may produce attractive graphs of results.
I believe that it is absurd--in most cases--to have to pay for something like this. The therapeutic principle here is of simply keeping track of a wide range of symptoms or problems systematically. The technology here is not a sophisticated x-ray machine or microscope -- rather, they are sets of simple questions such as "I'm a good person" or "My body hurts" (to be rated from 0-4).
I have jokingly thought of creating a questionnaire, to be marketed, with a full statistical analysis package and online access, called the "How Are You Doing" instrument (the HAY-D-1). It would consist of a single question, "How are you doing?" with the opportunity to choose from one of 5 responses. Perhaps there could be a published article demonstrating its reliability, validity, and correlations with other established research instruments.
Understandably, many researchers have worked long and hard to show useful results from their work. And it could be very desirable for them to have a way to earn a financial reward from the fruits of their labor. I suppose, in a free society, it is quite reasonable for people to attempt to sell such things, if people are willing to buy them.
But when there is this type of marketing and financial dealing going on, it can increase biases on the part of both the seller and the buyer. The buyer, having paid good money for questionnaires or "instruments," is more likely to think highly of their acquisition, due to cognitive bias (think again of Daniel Kahneman's work showing such effects). Perhaps therapists are more likely to rely on such purchased questionnaires rather than simply creating their own.
I think it could be useful, if questionnaires are to be used at all, to create custom symptom review questions. There is also some evidence that questions about the therapeutic alliance could be pertinent to therapeutic progress; these are absent from many symptom review surveys, including the OQ-45.
A nice idea in CBT is to have the clients or patients be actively involved in assessing and planning their own progress, instead of having the therapist be the "assessor." So, it could be a useful therapeutic exercise for clients or patients to design their own questionnaires, using their own language, and their own scale! The therapist could encourage and suggest a wide range of categories of questions to be followed, covering areas of physical, social, occupational, cultural, and psychological health, as well as a category about the therapeutic alliance, but the questions themselves could be designed by the client or patient! If statistical analysis was felt to be interesting or useful, we could easily design a simple app to create graphs, or use a spreadsheet -- we would not have to pay an extra fee for this!
So I support the idea of regularly conducting broad symptom reviews in psychotherapy, but I do not believe it is necessary to buy questionnaire packages. It could be even better to design one's own package, or collaborate with a patient or client to design a custom, personalized survey.