Assertiveness is the tendency to take charge, speak first and try to influence what other people do. It is not aggression, it is not confidence, and it says nothing about whether you are right.
Where it sits
In the Big Five, assertiveness is one of the six facets of extraversion, beside friendliness, gregariousness, activity level, excitement-seeking and cheerfulness. The ten statements the site uses are the assertiveness facet of the IPIP-NEO, such as Take charge and Can talk others into doing things, with reversed statements such as Wait for others to lead the way. You rate how accurately each describes you on five points, the reversed ones are flipped, and the ten are added, so a score runs from 10 to 50. The IPIP key page gives coefficient alpha of .84 for the scale. No norms have been published for it on its own, so the result is shown against the possible range rather than as a percentile.
What the research finds
Judge and colleagues (2002) found extraversion to be the Big Five trait most strongly linked to leadership, and the link is stronger for emerging as a leader than for leading well. Ames and Flynn (2007) looked at assertiveness on its own and found its relation to leadership is curved. People rated low on it were seen as failing to push for results, people rated high were seen as damaging working relationships, and those in the middle were rated the most effective. The benefits of assertiveness show up on the task side and its costs on the social side.
What it is not
It is not aggression. Aggression is getting your way at someone else’s expense, and in the Big Five that belongs to low agreeableness, not to extraversion. A person can be highly assertive and highly agreeable, as the trust guide describes.
It is not confidence or self-esteem. Quiet people can be sure of themselves and talkative people unsure.
It is not competence, and it is not being right. A high scorer states a view before being asked, whether or not the view is a good one.
A low score is not timidity. Low scorers hold views and act on them; they prefer to influence by example, in writing or after listening.
What it means for your results
A high score means you tend to take the lead and say what you want; a low score means you tend to wait and hold back. With no norms for the scale alone, a marker near the top of the range means your answers were near the top, not that you are in a top percentile. The 120-item Big Five test scores the same facet against a sample of over 400,000 people and shows the other five facets of extraversion beside it.
The assertiveness test takes two minutes, is scored on your device and shows your score on the strip.