What is an interest inventory?

An interest inventory is a questionnaire that asks how much you would like to do various work activities, and scores the pattern in your answers into a small number of interest categories. It does not have right answers, it does not test you on anything, and there is nothing to prepare for.

The most widely used framework behind them is Holland's six categories — Realistic, Investigative, Artistic, Social, Enterprising and Conventional. Score them, take your top three, and you have a Holland code that can be compared against the same six ratings assigned to occupations.

They are used by school careers services, university advisors, employment agencies and vocational rehabilitation programmes, mostly as a conversation starter rather than an answer. That is the right way to use one.

This is the distinction that matters most, and the one most commonly collapsed. An interest inventory asks what you want to do. An aptitude test asks what you can do. Neither substitutes for the other, and each is useless for the other's question.

The two are positively correlated in real populations, which is exactly what makes the confusion easy — people tend to get better at what they are willing to keep doing, and to enjoy what they are already good at. But the correlation is far from perfect, and the gaps are where careers go wrong in both directions: people who are good at something they find dull, and people drawn to work they have no aptitude for and no plan to acquire it.

A free online test is essentially always an interest inventory. Real aptitude testing is proctored, timed, and normed against a comparison group, and is not something a website can do while you sit on a sofa.

An IQ test is a specific kind of aptitude measure — general cognitive ability — and shares the aptitude column above. It says nothing about what work you would enjoy, and using one to choose a direction is a category error.

A personality test sits closer to an interest inventory than an aptitude test does, and the two genuinely overlap: openness tracks Artistic and Investigative interests, extraversion tracks Enterprising and Social ones, conscientiousness tracks Conventional ones. But the correlations are moderate, and one interest area — Realistic — has no dependable personality correlate at all. Nothing in the five-factor model predicts whether someone wants to work with their hands.

So if your question is specifically about work, ask about work. Sixty questions about work activities is a better instrument for that than inferring it from five trait scores, which is why this site offers both and does not pretend the personality one answers the career question.

The three you are most likely to meet:

The O*NET Interest Profiler is published by the U.S. Department of Labor, is free, is in the public domain under a Creative Commons licence, and links directly to their occupation database. It is the instrument this site uses.

The Strong Interest Inventory is commercial, must be administered through a certified practitioner, and typically costs money. It is longer, reports on more scales, and has a large research literature behind it.

The Self-Directed Search, developed by Holland himself, is designed to be self-administered and self-scored, and is also commercial.

They rest on the same six-category framework and, for the question most people bring to them, will not disagree much. The free one is not a lesser version of the paid ones; it is a shorter one from a different publisher.

Treat the output as a list of things to investigate, not as an answer. The failure mode of these instruments is not that they are wildly inaccurate — it is that people accept a ranked list as a verdict and skip the part where they go and find out what the work is actually like.

The cheap version of finding out: read the day-to-day description of three occupations from the list, not the job title. Find one person doing each and ask what the worst part of the week is. That single question is worth more than any test, including this one, because it tells you what the work is when nobody is selling it to you.