Lesson 15Estimating Population Measures of Center

Learning Goal

Let’s use samples to estimate measures of center for the population.

Learning Targets

  • I can consider the variability of a sample to get an idea for how accurate my estimate is.

  • I can estimate the mean or median of a population based on a sample of the population.

Lesson Terms

  • interquartile range (IQR)

Warm Up: Describing the Center

Problem 1

Would you use the median or mean to describe the center of each data set? Explain your reasoning.

Heights of 50 basketball players

A histogram of height inches with data from 66 to 80

Ages of 30 people at a family dinner party

A histogram of age in years with data from 5 to 50

Backpack weights of sixth-grade students

A dot plot of backpack weight in kilograms with data from 0 to 9

How many books students read over summer break

A box plot of number of books with minimum at 2, lower quartile at 5, median at 8, upper quartile at 10, and maximum at 15

Activity 1: Three Different TV Shows

Problem 1

Here are the ages (in years) of a random sample of 10 viewers for 3 different television shows. The shows are titled, “Science Experiments YOU Can Do,” “Learning to Read,” and “Trivia the Game Show.”

sample 1

  • 6

  • 6

  • 5

  • 4

  • 8

  • 5

  • 7

  • 8

  • 6

  • 6

sample 2

  • 15

  • 14

  • 12

  • 13

  • 12

  • 10

  • 12

  • 11

  • 10

  • 8

sample 3

  • 43

  • 60

  • 50

  • 36

  • 58

  • 50

  • 73

  • 59

  • 69

  • 51

  1. Calculate the mean for one of the samples. Make sure each person in your group works with a different sample. Record the answers for all three samples.

  2. Which show do you think each sample represents? Explain your reasoning.

Activity 2: Who’s Watching What?

Problem 1

Here are three more samples of viewer ages collected for these same 3 television shows.

sample 4

  • 57

  • 71

  • 5

  • 54

  • 52

  • 13

  • 59

  • 65

  • 10

  • 71

sample 5

  • 15

  • 5

  • 4

  • 5

  • 4

  • 3

  • 25

  • 2

  • 8

  • 3

sample 6

  • 6

  • 11

  • 9

  • 56

  • 1

  • 3

  • 11

  • 10

  • 11

  • 2

  1. Calculate the mean for one of these samples. Record all three answers.

  2. Which show do you think each of these samples represents? Explain your reasoning.

  3. For each show, estimate the mean age for all the show’s viewers.

  4. Calculate the mean absolute deviation for one of the shows’ samples. Make sure each person in your group works with a different sample. Record all three answers.

    Learning
    to Read

    Science
    Experiments
    YOU Can Do

    Trivia the
    Game Show

    Which sample
    number?

    MAD

  5. What do the different values for the MAD tell you about each group?

  6. An advertiser has a commercial that appeals to 15- to 16-year-olds. Based on these samples, are any of these shows a good fit for this commercial? Explain or show your reasoning.

Activity 3: Movie Reviews

Problem 1

A movie rating website has many people rate a new movie on a scale of 0 to 100. Here is a dot plot showing a random sample of 20 of these reviews.

A dot plot for movie ratings with one dot at 10, 20, 30, and 60. Two dots at 80, three dots at 85, 90, and 100. Five dots at 95.

  1. Would the mean or median be a better measure for the center of this data? Explain your reasoning.

  2. Use the sample to estimate the measure of center that you chose for all the reviews.

  3. For this sample, the mean absolute deviation is 19.6, and the interquartile range is 15. Which of these values is associated with the measure of center that you chose?

  4. Movies must have an average rating of 75 or more from all the reviews on the website to be considered for an award. Do you think this movie will be considered for the award? Use the measure of center and measure of variability that you chose to justify your answer.

Are you ready for more?

Problem 1

Estimate typical temperatures in the United States today by looking up current temperatures in several places across the country. Use the data you collect to decide on the appropriate measure of center for the country, and calculate the related measure of variation for your sample.

Lesson Summary

Some populations have greater variability than others. For example, we would expect greater variability in the weights of dogs at a dog park than at a beagle meetup.

Dog park:

  • Mean weight: 12.8 kg

  • MAD: 2.3 kg

A picture of 2 small dogs, 2 medium sized dogs, and 3 large dogs.

Beagle meetup:

  • Mean weight: 10.1 kg

  • MAD: 0.8 kg

A picture of 7 similar sized beagle dogs.

The lower MAD indicates there is less variability in the weights of the beagles. We would expect that the mean weight from a sample that is randomly selected from a group of beagles will provide a more accurate estimate of the mean weight of all the beagles than a sample of the same size from the dogs at the dog park.

In general, a sample of a similar size from a population with less variability is more likely to have a mean that is close to the population mean.