How much money do high school students carry with them?
How tall is the elm tree in Laura’s backyard?
What is the governor’s favorite ice cream flavor?
What proportion of Texas residents would choose vanilla as their favorite ice cream flavor?
How tall are the elm trees on Elm Street?
Statistical Question
For each question categorize the study as either an Observational Study or an Experimental Study.
Remember:
Observational Study: Researchers don’t assign choices; they simply observe them.
Experimental Study (Experiment): Researchers assign subjects to different treatments.
An experiment requires a random assignment of subjects to treatments.
Question 2
2.
Categorize the studies:
Over a 4‐month period, among 30 people with bipolar disorder, patients who were given a high dose (10g/day) of omega‐3 fats from fish oil improved more than those given a placebo. (Archives of General Psychiatry 56 [1999]: 407)
The leg muscles of men aged 60 to 75 were 50% to 80% stronger after they participated in a 16‐week, high‐intensity resistance‐training program twice a week. (Journal of Gerontology 55A [2000}: B336)
Among a group of disabled women aged 65 and older who were tracked for several years, those who had a vitamin B12 deficiency were twice as likely to suffer severe depression as those who did not. (American Journal of Psychology 157 [2000]: 715)
Observational Study
Experiment
Question 3
3.
Categorize the studies:
In 2002, the journal Science reported that a study of women in Finland indicated that having sons shortened the lifespan of mothers by about 34 weeks per son, but that daughters helped to lengthen the mothers’ lives. The data came from church records from the period 1640 to 1870.
Some gardeners prefer to use nonchemical methods to control insect pests in their gardens. Researchers have designed two kinds of traps, and want to know which design will be more effective. They randomly choose 10 locations in a large garden and place one of each kind of trap at each location. After a week, they count the number of bugs in each trap.
In 2001 a report in the Journal of the American Cancer Institute indicated that women who work at nights have a 60% greater risk of developing breast cancer. Researchers based these findings on the work histories of 763 women with breast cancer and 741 women without the disease.
Experimental Study
Observational Study
Question 4
4.
Categorize the following studies (all are observational) as Retrospective(looking back) or Prospective(looking forward):
A recent study in Europe looked at a large group of women of childbearing age. The researchers asked each woman how much alcohol they had consumed over the past 12 months. The researchers found that women who drank moderate amounts of alcohol were somewhat less likely to have infertility than women who did not. (November, 2001).
A group of disabled women aged 65 and older were tracked for several years, those who had a vitamin B12 deficiency were twice as likely to suffer severe depression as those who did not. (American Journal of Psychology 157 [2000]: 715)
The leg muscles of men aged 60 to 75 were measured at the beginning of a study. The leg muscles were found to be 50% to 80% stronger after they participated in a 16‐week, high‐intensity resistance‐training program twice a week. (Journal of Gerontology 55A [2000}: B336)
Restrospective Observational Study
Prospective Observational Study
Question 5
5.
Each week, the Gallup Poll surveys about 1500 adult U.S. residents to determine current opinions on a wide variety of issues. Identify the population and sample in this setting.
Question 6
6.
Question 7
7.
Question 8
8.
Question 9
9.
Some gardeners prefer to use nonchemical methods to control insect pests in their gardens. Researchers have designed two kinds of traps, and want to know which design will be more effective. They randomly choose 10 locations in a large garden and place one of each kind of trap at each location. After a week, they count the number of bugs in each trap.
Is this an observational study or an experiment?
Question 10
10.
Some people who race greyhounds give the dogs large doses of Vitamin C in the belief that the dogs will run faster. Investigators at the University of Florida tried three different diets in random order on each of five racing greyhounds. They were surprised to find that when the dogs ate high amounts of Vitamin C they ran more slowly.
Is this an observational study or an experiment?
Question 11
11.
A recent study in Europe looked at a large group of 350 women of childbearing age. The researchers asked each woman how much alcohol they had consumed over the past 12 months. The researchers found that women who drank moderate amounts of alcohol were somewhat less likely to have infertility than women who did not.
Select the population and the sample.
Question 12
12.
Question 13
13.
Question 14
14.
The band director at a high school wants to know what percentage of parents supports a decrease in the budget for fine arts. Because many parents attend the school’s annual musical, the director surveys the first 30 parents who arrive at the show.
Is the proportion of parents in the sample who support the decrease likely greater than or less than the proportion of all parents in the school who support the decrease?
Question 15
15.
The quality-control department at an automobile factory checks the tightness of motor-mounting bolts installed by assembly-line workers by sampling the first 25 cars produced by the assembly line each day.
Explain why this sampling method is biased.
Question 16
16.
The quality-control department at an automobile factory checks the tightness of motor-mounting bolts installed by assembly-line workers by sampling the first 25 cars produced by the assembly line each day.
Is this method likely to overestimate or underestimate the proportion of bolts that are improperly tightened?
Why?
Non-statistical Question
A large retailer prepares its customers’ monthly credit card bills using a machine that folds the bills, stuffs them into envelopes, and seals the envelopes for mailing.
Are the envelopes completely sealed?
Inspectors choose 40 envelopes at random from the 1000 stuffed each hour for visual inspection. Identify the population and sample in this setting.
The population is the 1000 stuffed envelopes each hour
The sample is the 40 envelopes chosen at random each hour
The population is all stuffed envelopes from a large retailer
The sample is the 1000 stuffed envelopes each hour
The sample is all stuffed envelopes
The population is the 40 envelopes chosen at random each hour
How much vitamin C does a popular brand of orange juice contain?
A nutrition magazine measures the amount of vitamin C in 50 half-gallon containers of a popular brand of orange juice from 10 different grocery stores and concludes that the containers produced by this company do not have as much vitamin C as advertised.
Identify the population and sample in this setting.
The population is half gallon containers of a popular brand of orange juice from 10 different grocery stores
The sample is all half gallon containers of a popular brand of orange juice
The population is all half gallon containers of a popular brand of orange juice
The sample is all half gallon containers of a popular brand of orange juice from 10 different grocery stores
The population is all half gallon containers of orange juice
The sample is all half gallon containers of orange juice
subjects are being observed to check for a difference
treatment is being controlled to check for an effect
an experiment
more information is needed to determine
an observational study
subjects are being observed to check for a difference
more information is needed to determine
treatment is being controlled to check for an effect
an observational study
The population is all women who drink moderate amounts of alcohol.
The sample is women who were infertile in the past 12 months.
The population is the large group of 350 women of childbearing age.
The sample is the large group of 350 women of childbearing age.
A department store mails a customer-satisfaction survey to people who make credit card purchases at the store. This month, 45,000 people made credit card purchases. Surveys are mailed to 1000 of these people, chosen at random, and 137 people return the survey form.
Identify the population and sample in this setting. Read carefully!
The population is the 45,000 people that made credit card purchases.
The sample is the 1000 people that were mailed a survey.
The sample is the 45,000 people that made credit card purchases.
The sample is the 137 people that returned the survey.
The population is all people that shop with credit cards.
The population is the 1000 people that were mailed a survey.
The band director at a high school wants to know what percentage of parents supports a decrease in the budget for fine arts. Because many parents attend the school’s annual musical, the director surveys the first 30 parents who arrive at the show.
Explain why this sampling method is biased.
Choose all the correct answers.
The majority of parents that attend the musical have children in the fine arts program
The survey method does not include randomization
Only the first 30 parents who arrived at the show were surveyed
This survey method is not biased, every parent had the opportunity to be one of the first 30
Not every parent had an equal opportunity to be surveyed
Every parent had an equal opportunity to be surveyed
The proportion of parents in the sample who support a decrease in the fine arts budget is likely less than the proportion of ALL parents in the school who support the decrease
because the sample would contain a high proportion of parents that had students in the fine arts program
All cars produced have an equal opportunity of being sampled.
Not all cars produced have an equal opportunity of being sampled.
The first 25 cars produced each day will have better quality since workers just arrived and are not tired.
The method is not randomized.
Employees are fresh at the job and less likely to make mistakes.