📈 Probability Explained
Probability Explained
A simple explanation of how independent probabilities stack into combinations.
Method FAQ
Is Avortas scientific research?
No. It’s an educational, curiosity-first calculator that uses probability-style thinking.
Why do you use 8.2 billion?
It’s a simple global population frame to make comparisons intuitive.
How can I interpret results responsibly?
Treat them as estimates and entertainment—real-world distributions are complex.
Why independent things multiply
If one person in four has a given trait and one in five has another, and the two have nothing to do with each other, then one in twenty has both. You multiply because each condition cuts the remaining group by its own share: a quarter of everyone, then a fifth of that quarter.
Add a third trait at one in ten and you are at one in two hundred. A fourth at one in three and you are at one in six hundred. This is why combination rarity climbs so quickly, and why almost any list of five or six traits produces a number that sounds astonishing.
Which is the honest catch
Everyone is rare, if you measure enough things. Take twelve independent traits that half the population each shares and the average person is one in four thousand. Take twenty and they are one in a million. That number is not evidence the person is unusual; it is evidence that twenty questions were asked. A rarity score describes how many questions were asked at least as much as it describes the person answering them.
What “1 in 10,000” actually claims
It is a statement about a population, not a prediction about you. In a country of forty million it says roughly four thousand people are expected to match. Nobody has counted them. It is what the frequencies imply if they are right and if the traits are independent, and those two conditions are doing real work in the sentence.
Where multiplying goes wrong
Traits that share a cause are not independent. Eye colour and hair colour are the clearest case: the same pigmentation genes drive both, so combinations that tend to run together are more common than the product suggests, and combinations that rarely co-occur are rarer. Multiplying treats every pair as unrelated, so it understates the rarity of concordant combinations and overstates it for discordant ones. No correction is applied on this site, and saying so plainly is more useful to you than a number carrying a precision it has not earned.
Why the last digits are fiction
An input given as 12% may really be anything from 11.5% to 12.5%. Multiply three such numbers and the uncertainty compounds faster than the answer does. That is why every result here is rounded to two significant figures, and why small headcounts are withheld entirely rather than printed and quietly disbelieved — see How We Calculate Rarity and Data Sources.
Last reviewed September 2026.