Definition: A simple random sample is a sample chosen so that every member of the population has an equal chance of being selected.
What is a simple random sample?
It is a sample picked by chance, so each person or item has the same likelihood of selection. It avoids bias and tends to represent the whole population.
How do you take one?
Number every member, then draw numbers from a hat or use a random number generator. To survey 40 students from a school of 800, assign each student a number from 1 to 800 and generate 40 different random numbers.
Why does it matter?
A biased sample gives misleading results. Asking only the chess club about favorite hobbies does not represent the school. Surveying every 20th person entering the gym is not random if a group enters at the same time.
What can you do with it?
Use sample data to make inferences about the population. If 14 of 40 sampled students walk to school, about 14/40 = 35 percent of 800, or 280 students, probably walk.
What is a common mistake?
Thinking a bigger sample fixes bias. A huge online poll of volunteers is still biased because people chose themselves.