Type A vs Type B Personality: What the Evidence Actually Shows

Type A describes a person who is competitive, driven by deadlines, quick to feel that time is running out, and quick to irritation when something blocks them. Type B describes the other end of that scale: patient, steady, tolerant of delay, and measured against their own standard rather than against a rival. Most people sit somewhere in between, and the two labels are a rough sort rather than two separate kinds of human being.

The labels come from cardiology, not psychology. Two San Francisco cardiologists, Meyer Friedman and Ray Rosenman, described the pattern in the late 1950s because they believed it predicted heart attacks. That is the part almost every article on this topic repeats, and almost none of them follow up on. The prediction held in the first large study and then largely failed to replicate over the following thirty years. What survived is narrower: hostility, not hurry.

So the honest answer to "which type wins in a startup" is that neither label predicts much on its own. The traits underneath them do. Below: the differences side by side, then the evidence trail, then what the findings that survived mean for someone building a company.

Type A and Type B differ on pace, on how scarce time feels, on whether progress is measured against rivals or against yourself, and on what happens under pressure. These are the contrasts Friedman and Rosenman described and that later questionnaires such as the Jenkins Activity Survey tried to measure. Read them as ends of a scale, not as boxes.

The original evidence was strong. The Western Collaborative Group Study enrolled 3,524 men aged 39 to 59 at ten California companies in 1960; the 3,154 who were free of heart disease at intake were followed for eight and a half years. By the end, 257 had developed clinical coronary heart disease, and Type A men developed it at roughly twice the rate of Type B men, independent of smoking, blood pressure and cholesterol. Published in 1975, it was one of the most influential findings in behavioural medicine, and it is how the labels entered ordinary language.

Then the replications stopped working. A systematic review published in 2002 covered 18 studies asking whether Type A caused heart disease and 15 asking whether it predicted outcomes in people who already had it, and found that the studies reporting a significant association were in the minority in both groups. Large later cohorts in France, Northern Ireland and Japan found no association between Type A and coronary events, and pooled analyses of prospective studies found none either.

There is also an uncomfortable footnote. A 2012 paper in the American Journal of Public Health documented that the tobacco industry funded a substantial share of Type A research, because a behavioural cause of heart disease was useful to an industry defending a chemical one. The authors describe the pattern of strong early findings followed by null results as a decline effect that the funding helps explain. None of this means Friedman and Rosenman were dishonest. It does mean the confident version of the Type A story that circulates online is not what the literature supports.

The part of the Type A pattern that survived replication is hostility, not hurry. When the global label failed to hold, researchers went looking for the component that did, and the answer that kept coming back was irritability, cynicism and readiness to take offence, rather than ambition or fast walking.

The best summary of that evidence is a 2009 meta-analysis in the Journal of the American College of Cardiology by Yoichi Chida and Andrew Steptoe. Pooling 25 prospective studies of initially healthy people, anger and hostility were associated with a 19% higher rate of later coronary events (hazard ratio 1.19, 95% confidence interval 1.05 to 1.35). Across 19 studies of people who already had heart disease, the association was similar (hazard ratio 1.24, 1.08 to 1.42). Those are real but modest effects, and they attach to one component of the pattern rather than to the label as a whole.

For a founder, that is the distinction worth keeping. Working hard and fast is not the part the evidence implicates. Being angry about it is.

Type A and Type B are not Big Five traits, and no serious personality inventory measures them as such. They are a bundle of behaviours that maps onto several Big Five facets at once, which is one reason the label predicts less than its parts do.

In the standard facet description of the Big Five, achievement striving and self-discipline sit under conscientiousness, while irritability and hostility sit under neuroticism, the opposite pole of emotional stability. Competitiveness and a low tolerance for other people’s pace look like low agreeableness. A classic Type A is, in Big Five terms, three separate dials turned up rather than one type.

That matters because the dials point in different directions for a founder. High conscientiousness predicts follow-through. Low agreeableness can help you hold an unpopular position and hurt you when you need a team to stay. High irritability mostly costs you, in health and in people. Sorting yourself into A or B averages all three into one crude answer.

• Achievement striving and self-discipline: facets of conscientiousness. Broadly an asset in a startup.
• Competitiveness and impatience with others: closer to low agreeableness. Useful in a fight, expensive in a team.
• Irritability and hostility: facets of neuroticism. The one component the heart-disease evidence actually implicates.

The Type A end of the scale fits businesses where speed is the moat and the window is short: land grabs, marketplaces racing to liquidity, categories where a competitor six months ahead compounds into a permanent lead. Urgency is genuinely informative in those markets, and a founder who feels time as scarce will set a pace the market rewards.

The founders below are assessments from public behaviour rather than diagnoses. Elon Musk runs closest to the caricature and shows both halves of it: compressed timelines that produced a launch cadence nobody thought possible, and a cost in turnover and public conflict that is just as well documented. Jeff Bezos turned Type A urgency into an operating principle rather than a temperament, with a stated bias for action and a refusal to let reversible decisions sit. Steve Jobs supplies the hostility component, and the record of what it cost the people nearest to him.

The pattern fails when a founder cannot tell urgency from importance. Deadline pressure applied to a research problem, a regulatory approval or a long enterprise sales cycle does not speed it up. It just spends the team.

The Type B end fits businesses where the advantage accumulates slowly and the expensive mistake is a rushed irreversible decision: deep technology, brands, regulated markets, anything where the quality of the thing is the distribution.

Jensen Huang spent more than two decades building Nvidia toward a use case that did not exist when he started in 1993. Patrick Collison built Stripe on documentation and developer trust, neither of which can be hurried. Yvon Chouinard built Patagonia while openly refusing growth that would have cost the company its reason to exist. None of these are low-ambition people. They are people whose sense of time matched the game they chose.

The failure mode is real too. A founder who is never rushed can let a hiring problem, a cash problem or a competitive threat sit for a quarter too long, and a quarter is a long time in an early company.

On the evidence, the question is badly formed. There is no study showing that Type A founders build more valuable companies than Type B founders, and anyone who says otherwise is extrapolating from a heart-disease literature that did not hold up for heart disease.

What the research does support is narrower and more actionable. Conscientiousness helps in almost any venture. The match between your natural pace and your market’s clock speed matters more than where you sit on the A to B scale. And hostility is the one component with a measured cost, so it is the one worth managing whichever end you are at.

The practical move is to stop sorting yourself into a binary invented to predict heart attacks, and measure the underlying traits instead.

The original assessment was a structured interview that scored how you answered as much as what you answered: whether you interrupted the interviewer, how fast you spoke, whether deliberately slow questions made you visibly impatient. Later questionnaires traded that for self-report and lost some of the signal, because these behaviours are easier to observe than to admit.

A better question than "am I A or B" is which of the three underlying dials is actually turned up in you: the drive, the competitiveness, or the irritability. Those move independently, they are measurable, and they tell you different things about how you should build.