Khan Academy
Random Sampling & Avoiding Bias
Techniques for fair sampling and the bias to watch for.
Watch on YouTubeWhy a fair, random sample lets you make valid inferences.
Read this first — it covers the idea in plain language with a worked example.
It's usually impossible to survey everyone, so we study a sample and use it to estimate facts about the whole population.
A random sample gives every member an equal chance of being selected. That keeps the sample representative and reduces bias.
Watch out for bias
Surveying only your friends, or only people in one place, can make a sample unrepresentative — even if the sample is large.
Watch the main video, then check the second take if you want another explanation.
Techniques for fair sampling and the bias to watch for.
Watch on YouTubeTry a worksheet or work through some problems before the quiz.
A couple of questions to make sure this topic stuck. Retake as many times as you want.
Random Sampling
Which sample is most likely to represent all students at a school?