Before You Watch

Every day we encounter uncertainty – will the traffic be heavy on your way to the shops, what is the chance of rain, is it likely the power grid will malfunction? Probability helps us to deal with this uncertainty by indicating the chance of events occurring. However, the probability of an event may differ depending on surrounding conditions.

For example, the probability that the traffic will be heavy depends upon the time of day you’re travelling. Similarly the chance of rain depends on the current season and other weather patterns leading up to the day in question. The chance of a power grid malfunctioning also depends on usage; if we’re in the middle of a heatwave then there may be a few more air conditioners being used (and thus draining the system) than during more comfortable conditions.

This video describes the concept of conditional probability and how it may be calculated. It is recommended you are familiar with the content in the Probability videos ‘What are the chances’ and ‘Tree diagrams’ before watching this video.

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Now What?

The next video introduces inferential statistics, which uses the probability calculated from sample data to infer information about the much larger population from which the sample was drawn.

But When Am I Going to Use This?

Whenever we have situations where surrounding conditions influence the chances of an outcome we may need to consider conditional probability.

For example, the probability of a medication being successful may be affected by the person’s age.

The chance of success may be greater for example for a teenager than for someone over 80. This may affect decisions surrounding the course of action a doctor may take or medication to prescribe.

 

Similarly the probability of a car tyre lasting a set period of time is likely conditional upon the brand of car tyre, or the way in which the car is driven.

In any situation where decisions are to be made, the underlying conditional chances of events helps inform the process.

Other Links

 Maths is fun takes you through the basics of probability and looks at some examples of conditional probability.

Khan Academy provides explanations of probability and conditional probability.

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