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9th grade · Math · Unit 5 of 17

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.

Arizona Academic Standards learning standard: A1.S-ID.A.2; A1.S-ID.A.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 Arizona

In the Arizona Academic Standards, this is unit 5 of 17 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: Arizona Department of Education

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 800 students. A survey asks 80 of them. What fraction of the students were surveyed? Type it in lowest terms.

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  2. Question 2

    In a random sample of 20 students, 8 said they walk to school. Based on this sample, about how many of 800 students walk?

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  3. Question 3

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

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  4. Question 4

    In statistics, the population is…

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

  5. Question 5

    Which is a primary source of data?

    • a textbook summary
    • a newspaper article about a survey
    • a survey you conducted yourself
    • an online comment

  6. Question 6

    Which sample is most likely to represent all students at a school?

    • the 50 students on the basketball team
    • 50 students who volunteered online
    • 50 students chosen at random from the school list
    • 50 students at the lunch table nearest the gym

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