Cogito
Probability and Statistics · Chapter 7 · Lesson 1
Samples and Bias
Who did you actually ask?
12 problems · about 21 minutes · TEKS P.S.4.A, S-IC.B.3
What this lesson teaches
The student identifies sampling methods and sources of bias.
- A sample stands in for a population, so it must represent it.
- Randomness is what protects against bias.
- A larger sample makes a biased result more precise, not more correct.
Warm Up
Straightforward practice. Get the method working first.
5 problemsA magazine prints a survey and readers mail it back. Biased? 1 yes, 0 no.
Answer 1
Why Yes, voluntary response bias.
Why does a larger sample not fix bias?
Answer Bias is systematic, so more data repeats the same error.
Why It makes a wrong answer more precise.
Every individual has an equal chance. Is it a simple random sample? 1 yes, 0 no.
Answer 1
Why That is the definition.
Asking friends in the corridor. Convenience sample? 1 yes, 0 no.
Answer 1
Why Whoever is nearby.
Sampling within each year group separately. Stratified? 1 yes, 0 no.
Answer 1
Why Groups sampled separately.
Build It Up
The same ideas with more to keep track of.
3 problemsA survey in a library about libraries. Biased? 1 yes, 0 no.
Answer 1
Why Who is there to be asked?
Which matters more for accuracy? 1 method, 2 size.
Answer 1
Why Size cannot repair a biased method.
Is the population the group actually measured? 1 yes, 0 no.
Answer 0
Why That is the sample.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
4 problemsWhich are sources of bias?
Answer Voluntary response; Convenience sampling; A leading question
Why One of these is the cure rather than the disease.
A phone poll at 10am on a weekday. Does it miss working people? 1 yes, 0 no.
Answer 1
Why Who answers at that hour?
The Poll: An online poll where readers choose to respond. Is this voluntary response bias? 1 yes, 0 no.
Answer 1
Why Yes.
The Size: Does a larger sample fix bias? 1 for yes, 0 for no.
Answer 0
Why No.