**Probability** is the chance that an event will occur given as a mathematic ratio that states the number of possible events giving one outcome in relation to a total number of similarly possible events in all outcomes. This ratio is often used in gambling to determine the **odds**, or the degrees of advantage or disadvantage in a competition based on previous results.

According to Leonard McCoy, in 2267, the chances of contracting Sakuro's Disease are literally **billions to one**. (TOS: "Metamorphosis")

In 2269, Spock determined the probability of the Insectoid pod ship being dead at being **.997** accurate. (TAS: "Beyond the Farthest Star")

After succumbing to rapid aging, caused by Taurean headbands, Spock hypothesized that there was a possibility that the transporter could be used to restore the landing party to their original ages. Unfortunately, at the time, the odds were against the aged crewmembers **99.7-to-1**. (TAS: "The Lorelei Signal")

Later that year, Spock determined the probability of Harry Mudd being found on the planet Motherlode to be **81% ± .53**, which was, in his words saying: "Mudd is probably there." (TAS: "Mudd's Passion")

Later yet that year, Spock determined the probability of **approximately 82.5%** that one of the members of the Vedala search party, assigned to find the Soul of the Skorr, was an saboteur. (TAS: "The Jihad")

In a tactical projection of possible future Romulan deployments along the Romulan Neutral Zone, Data determined that their ships were deployed to support a policy of confrontation designed to test Federation defenses along the Neutral Zone. With this analysis, he projected a **90%** probability that they would continue to pursue this policy. (TNG: "Data's Day")

In 2370, an alien visiting Deep Space 9 named Cos introduced a gambling machine to Martus Mazur that was able to manipulate the laws of probability. Jadzia Dax later discovered this abnormality when she observed that the spin of **over 80%** of the solar neutrinos in the space station were spinning clockwise, when the given probability was that **about 50%** of should be spinning clockwise and the **other 50%** spinning counterclockwise. (DS9: "Rivals")

One skill necessary for a dabo girl was being able to calculate odds in one's head quickly. Leeta confessed this to a masseur in 2373 while receiving his ministrations. (DS9: "Let He Who Is Without Sin...")

During the opening months of the Dominion War, Julian Bashir calculated his shipmates having a **32.7%** chance of surviving the war. (DS9: "A Time to Stand")