Probabilities crop up in the news, documentaries and blogs everyday. They cover a wide range of activities: will it rain today?, what are chances of becoming ill ?, or to place a bet or not? They seem to cover most aspects of life. But what is a probability?
When we flip a coin into the air to decided whether to stay in and watch TV or go out for a meal, then as it twists and turns there is no way to predict which way it will land. The decision has been left to a random outcome. It could land heads, or it could land tails. There is no way to predict. To quantify the uncertainty we calculate a probability. To do this we need to know the number of possible outcomes, in the case of a coin it is 2 - landing heads or landing tails. Therefore the probability of landing heads is 1 of 2 possible events which gives “1 in 2 chance of heads” or a probability of 1/2 or 0.5 ( in percentages “50% chance of landing heads” or in gambling terminology “evens” ). All probabilities follow the same principles but the calculations can be different.
In the case of predicting the weather it can’t be flipped up in the air like a coin ! Instead, the UK Meteorological Office uses mathematical models. The models describe the relationship between a very large number of variables for example temperature, pressure, wind speed and direction at points across the country. Combining the models with measurements from weather stations they use lightening fast computers to calculate the probability of rain in a region. Chances of rain are watched eagerly by farmers about to harvest their crops, events organisers wondering how many umbrellas to order, and supermarkets making sure they have enough ice cream to sell.
To plan the amount of resources required for patients, health organisations use medical records to calculate probabilities of developing a disease. In the case of cancer, medical records show how many people have developed one of the many different forms during a lifetime. All this information is gathered together and probabilities are calculated. For example in the UK population there is a 1 in 3 chance of developing cancer at some point in a lifetime.
Gambling is big business, in the UK it is approximately £14bn per year, and covers many activities from sport to whether it will snow on Christmas Day. Take football, at the beginning of the football season all teams have an equal chance of coming top of the league table by the end of the season. However, some teams have a stronger squad of players, or new managers bring different ideas about improving the performance of the team, and so on. Bookmakers take all of the factors and assess the chances of a particular team winning the league and offer odds, say 6-1 ( “6 to 1” ). In other words, the bookmaker thinks there is 6 times more chance of the team not winning the league compared to it winning ( equivalent probability is “1 chance in 7” or 14% chance of winning ). A gambler ( or punter ) places an amount of money with the bookmaker hoping that they are wrong and they win lots of money !
Probabilities quantify the level of uncertainty that a particular event will occur - they are a guide and not a prediction. They can be used to plan for rainy days, help the health system to prepare for future illnesses, and avoid losing money !