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9th grade · Math · Unit 5 of 22

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.

New York State Learning Standards learning standard: AI-S.ID.2; AI-S.ID.3 · 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 New York

In the New York State Learning Standards, this is unit 5 of 22 in 9th grade Math, after Linear Relations and before Number Sets.

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: New York State Education Department (NYSED)

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 200 students. A survey asks 20 of them. What fraction of the students were surveyed? Type it in lowest terms.

    answer box

  2. Question 2

    In a random sample of 40 students, 12 said they walk to school. Based on this sample, about how many of 600 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

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

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

  5. Question 5

    Ice cream sales and sunburns both rise in summer. What can we conclude?

    • They are related to the season, but one does not necessarily cause the other.
    • Ice cream causes sunburn.
    • Sunburn causes ice cream sales.
    • Nothing is related.

  6. Question 6

    A graph's vertical axis starts at 90 instead of 0, making a small change look huge. This is…

    • a misleading graph
    • a larger sample
    • a reliable graph
    • a random sample

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