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9th grade · Math · Unit 14 of 18

Statistics in Society

Samples, bias and misleading graphs

What your child practices

Telling a population from a sample, spotting bias in who is asked and how, predicting from a sample, noticing misleading graphs, and why correlation is not causation.

Alabama Course of Study content standard: GDA.10; GDA.11 · comparing the center and spread of data sets and the effect of outliers

How we explain it

Children can open this short lesson before they practice.

  1. A sample is a smaller group chosen to stand for a whole population.
  2. A random, large sample is fairer. Bias happens when some people are left out.
  3. Data is reliable when you get similar results each time.

Example: A survey about school lunch asks only students in the cafeteria line. Is it fair? It leaves out students who do not buy lunch. That makes the sample biased. Answer: No, it is biased

Statistics in Society in Alabama

In the Alabama Course of Study, this is unit 14 of 18 in 9th grade Math, after Data & Scatter Plots and before Two-Way Tables & Causation.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alabama State Department of Education (ALSDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    A school has 600 students. A survey asks 120 of them. What fraction of the students were surveyed? Type it in lowest terms.

    answer box

  2. Question 2

    In a random sample of 50 students, 20 said they walk to school. Based on this sample, about how many of 400 students walk?

    answer box

  3. Question 3

    Four students report hours of sleep: 7, 8, 9, 8. What is the mean?

    answer box

  4. Question 4

    In statistics, the population is…

    • the people who answered
    • the number of questions
    • the average of the data
    • the whole group you want to learn about

  5. Question 5

    A poll is conducted by phoning only landlines on weekday mornings. Who might be missing?

    • only teachers
    • people who work during the day or only use cell phones
    • nobody
    • people who answer the phone

  6. Question 6

    A survey about screen time asks, “Don't you agree that too much screen time is harmful?” What is the problem?

    • The question is leading and may bias the answers.
    • The sample is too random.
    • Nobody uses screens.
    • The question is too short.

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