Sampling

1. A research team conducted a survey to determine whether people in a particular city preferred buying organic or conventionally grown fruits and vegetables.  The researchers surveyed 245 people at local farmers' markets in different parts of the city. Which of the following factors makes it least likely that the results of the survey will provide reliable conclusions about the fruit-buying preferences of all of the people in the city?

1. The sample size.
2. The population size.
3. The number and locations of the farmers' markets.
4. The use of farmers' markets as survey sites. 

2. A high school receives a grant of $2,000.  A group of students conduct a research project to decide if the school should spend the money on more sports equipment or extra materials for the Advanced Placement teachers. The students survey 100 students that they approach randomly during nutrition, at locations scattered across the campus. Which of the following changes to their sampling plan would support their claims that their conclusions represent the opinions of the entire student body?

1. Survey an additional 50 students at a football game.
2. Survey 40 more students, during nutrition at various locations on campus. 
3. Survey an additional 100 students at the Honors Society meeting. 
4. Add 50 parents to the study.

3. Researchers are conducting a research project that is designed to test the efficacy of a weight loss drug.  Researchers recruited 100 obese men to the study.  Half of the men were assigned to receive the weight loss drug.  The other 50 were not assigned to receive the weight loss drug.  At the end of the study, the men who had not received the drug weighed, on average .6 pounds more than they had at the start of the study. The men who had received the drug weighed, on average 6.5 less than they did when they started the study. Which conclusion can we draw from this study?

1. The weight loss drug is effective at helping obese people lose weight.
2. Not taking a weight loss drug causes men to gain weight.
3. The weight loss drug helps obese men lose a moderate amount of weight.
4. The weight loss drug is the best drug available to improve the health of obese men.

4. Traffic engineers want to test the effectiveness of blinking "Pedestrian Crossing" signs at crosswalks in preventing accidents. They place blinking signs at 10 crosswalks around a city. Six months later, they compare accident data.  They find that, at 6 of the crosswalks, accidents have decreased by 35% since the installation of the blinking signs.  At 3 crosswalks, the accident rates remained about the same.  At the last crosswalk, accident rates increased by 5%. What reasonable conclusion can be drawn from the study?

1. Blinking signs decrease crosswalk accidents at some locations, but more research is needed to determine which locations respond best to blinking signs.
2. Blinking signs should be installed at all crosswalks to decrease accidents.
3. Blinking signs are mostly ineffective at decreasing accidents at crosswalks. 
4. Blinking signs cause a significant decrease in crosswalk accidents, but because they can also cause increases in accident rates, they should not be used. 

5. A group of researchers believe that using educational program on iPads can significantly increase pre-reading skills in preschoolers.  They recruit 10 preschools that serve low-income students.  At 5 of the schools, they donate a set of iPads and ask teachers to have students spend 30 minutes a day working on phonics games. At the other 5 schools, they ask teachers to have students spend 30 minutes a day playing art games. At the end of the school year, students who did the phonics games improved their reading skills by an average of 20%. Students who did the art program improved their reading skills by an average of 19%.  What reasonable conclusion can be draw from this study?

1. iPad phonics games help low-income preschoolers significantly improve their reading skills. 
2. iPad phonics games hurt low-income preschoolers' reading skills.
3. Low-income preschoolers improve their reading skills over the course of the preschool school year.
4. All preschoolers improve their reading skills over the course of the preschool school year.