Almost every career test in the world rests on one idea: that people are happier in work that matches their interests. It is a reasonable idea and there is real evidence for it. The question is how much of the picture it explains.
The most comprehensive answer available comes from Hoff, Song, Wee, Phan and Rounds (2020), published in the Journal of Vocational Behavior. They reviewed 105 studies spanning more than sixty years, with a combined sample of 39,602 people. The relationship between interest fit and overall job satisfaction came out at a correlation of 0.19.
Squared, that is under 4 per cent of the variance in whether someone is satisfied at work.
Earlier meta-analyses found the same territory — around 0.17 in 2005, around 0.21 in 1987. Nobody in the field disputes this. It is simply not something you will find on a product page.
What interest does predict
Interest congruence relates more strongly to job performance, at around 0.32 — closer to 10 per cent of variance. And the 2020 analysis found the relationship was stronger for particular facets of satisfaction than for the global measure, with satisfaction with one's choice of job among the strongest.
For a fifteen-year-old choosing a stream, that facet is exactly the target. Nobody is trying to predict whether they will enjoy a job they will not hold for a decade. The question is whether the choice itself was well made.
What this means for how we built Marga
It means interest cannot be the answer. It can be the router.
The interest questions tell us which region of work to look at. What happens after that is a different kind of measurement: what does work in that region actually require, and where does this student stand against it. That second part is where the useful information is, and it is the part nobody in this market builds.
Every product in this category measures roughly 4 per cent of the picture and presents it as five best-fit careers. We would rather publish the ceiling and then build past it.