Sample Size and Bias

Lab Brief #3

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

A conclusion is only as good as the sample it came from. Too small a sample is dominated by chance; a sample drawn from the wrong group is biased no matter how large. Both faults produce confident, wrong answers.

Key words

sample
The subset actually measured, standing in for a larger population.
sampling bias
A sample that systematically misrepresents the population it claims to describe.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

tape measure
notebook
calculator

⚠️ Safety first

Have an adult check your set-up before you start, and tidy everything away afterwards.

Step 1 of 4 · Read

Think about what you just learned: say what "sample" and "sampling bias" mean in your own words before you start.

Step 2 of 4 · Do

Estimate the mean height of your year group from a sample of five, then twenty, then the basketball team. Compare all three with the true mean and name the fault in the third.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

Sampling only the basketball team to estimate year-group height introduces:

How sure are you?😐 maybe

Question 2 of 2

A sample of five is unreliable mainly because it is dominated by:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

Next: How Scientific Consensus Forms All lessons

🎯

Next Smart Experiment

We'll pick an experiment that matches exactly how you're thinking right now.

✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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