6. Observational Studies and Experiments (Quiz)

A brand of popcorn instructs users to microwave for 90-120 seconds on high. A student wonders what the ideal microwave time for popcorn might be and designs an experiment to find out. Bags of popcorn are placed in the microwave for different lengths of time: 90 seconds, 100 seconds, 110 seconds, and 120 seconds. Also, 2 types of microwaves with different power capacity will be used: 900 watts and 1,000 watts. At the end of the experiment, the number of unpopped kernels will be counted. Using 3 lengths of time and 2 types of microwaves describes which part of the experiment? the levels the treatments the response variable the experimental units

A.

A clothing company is considering a new insulation for winter coats. To collect customer satisfaction data on the new insulation, the company is considering two methods. Method 1: The company offers the first 50 employees who volunteer to try out a coat with new insulation if they will report their satisfaction level after one month. At the end of the month, the 50 volunteers describe their satisfaction with the coat's performance. Method 2: The company takes 50 volunteers and randomly assigns 25 of them to coats with the new insulation and the other 25 to coats with the current insulation. All volunteers wear the coats for a month and then describe their satisfaction with the coats' performance. Which method describes an experiment? Method 2 is an experiment because both groups report their satisfaction with the coats. Method 1 is an experiment because all volunteers receive coats with the new insulation. Method 2 is an experiment because volunteers are assigned one of the two insulation types. Method 1 is an experiment because the volunteers' satisfaction with the new insulation can be measured.

C.

To find the ideal temperature for baking muffins, a student plans an experiment to assess the taste and texture of muffins baked at different temperatures. The student pours 3 batches of muffins from the same batter into baking cups and assigns them to different oven temperatures: 350 degrees, 375 degrees, or 400 degrees. Each batch is baked for 10 minutes, and after appropriate cooling time, the muffins are assessed for taste and texture. What is the explanatory variable in this experiment? the baking time the 3 batches of muffins the baking temperature the taste and texture of the muffins

C.

A home-improvement store offers a new brand of lawn food that claims to reduce the number of weeds by 30% over a different brand of lawn food. To test the claim, a homeowner plans to use the new brand of lawn food on half of his lawn and the original brand on the other half. The homeowner will count the number of weeds that appear after a month on each half of the lawn. A neighbor explains that there may be confounding variables, such as shade, that might also explain the relationship. Which statement best describes the effect of the confounding variables? Because of confounding variables, the homeowner should only put the new lawn food on shady spots and the original brand on sunny spots. Because shade is a primary cause of weed growth, the brand of lawn food used in shady or sunny spots will not affect the number of weeds. If the half of the lawn with the new lawn food shows fewer weeds after a month, this will prove the new lawn food is better at stopping weed growth. The parts of the lawn that receive the new lawn food may also get more shade than other parts of the lawn, and the shade might also cause fewer weeds.

D.

To increase attendance for a flower show, the organizers have chosen flower shops in the area to offer discount coupons to their customers. Half of the stores receive discount coupons for admission, while the other half of the stores receive two-for-one admission coupons. The organizers then compare the number of each type of coupon redeemed at the show. What are the explanatory and response variables in this scenario? The explanatory variable is the number of coupons redeemed. The response variable is the type of coupon. The explanatory variable is each chosen flower shop. The response variable is the number of coupons redeemed. The explanatory variable is the type of coupon. The response variable is number of number of coupons redeemed. The explanatory variable is the attendance at the flower show. The response variable is the number of attendees who used coupons.

C.

A farmer would like to determine if a new liquid fertilizer is an improvement compared with the fertilizer currently used. To collect data, two methods are considered. Method 1: Visit a local farm currently using the new liquid fertilizer and measure the heights of plants grown at the farm. Method 2: Choose a plot of land and divide it into 16 smaller plots. Randomly select 8 of the plots to use the new fertilizer and 8 of the plots to use the current fertilizer. Measure and compare plant heights in the 16 plots. Which statement about these methods is true? Method 1 is an experiment because the farm uses the new fertilizer. Method 2 is an experiment because there are 16 different plots used. Methods 1 and 2 are both experiments because both use the new fertilizer. Method 2 is an experiment because the plots are randomly assigned a fertilizer.

D.

An auto-parts store offers a fuel additive that claims to increase a vehicle's gas mileage. The additive is poured into a vehicle's gasoline tank after the tank is filled. To measure the claim, 30 taxi drivers receive a bottle of the additive to use the next time they fill their gas tank. The drivers then compare their gas mileage with the additive to their gas mileage before the additive was used. What is the response variable in this scenario? the age of the car the 30 cars used in the study the use of the additive the gas mileage after the additive is used

D.

An auto-parts store offers a fuel additive that claims to increase a vehicle's gas mileage. The additive is poured into a vehicle's gasoline tank after the tank is filled. To measure the claim, the store offers a free bottle of the additive to customers who drive SUV's, who then provide information about their gas mileage on the store website. A customer argues that the type of vehicle could be a confounding variable in this study. Which statement best describes the effect of the confounding variable? Because vehicles of different sizes may respond similarly to the additive, it should be easy to conclude whether the additive improves gas mileage. Because vehicles of different colors may show differences in gas mileage, the additive may improve the gas mileage in some vehicles but not in others. Because owners of different types of vehicles may choose not to use the additive, those vehicles will not show an improvement in gas mileage. Because vehicles of different sizes may respond differently to the additive, it may be difficult to conclude whether the additive improves gas mileage for all vehicles.

D.

Two methods are proposed to measure the effectiveness of a brand of sunscreen. Method A: Survey adults visiting a beach on a busy weekend. Ask each adult which brand of sunscreen they are using, and assess their arms for sun exposure. Method B: Volunteers are randomly assigned to one of two brands of sunscreen. Each volunteer is asked to report back at the end of the day, and their arms are assessed for sun exposure. Which statement is a correct interpretation of these methods? Both methods are experiments because sun exposure is assessed in both methods. Both methods are observational studies because neither method attempts to influence responses. Method A is an experiment because it compares many brands of sunscreen, while method B is an observational study. Method B is an experiment because it randomly assigns volunteers a sunscreen, while method A is an observational study.

D.

To increase attendance for a flower show, flower shops in the area offered discount coupons to their customers. Show attendance was higher this year, which the organizers attributed to the many discount coupons attendees used. However, the organizers are warned that weather could be a confounding variable in interpreting the rise in attendance. Which statement could explain the effect of confounding? Because the weather was worse last year, fewer coupons were distributed compared to this year. Because the weather was similar in both years, it most likely played no role in the attendance increase. Because coupons were handed out this year and not last year, the weather was different this year compared to last year. Because the weather was generally better this year compared to last year, the attendance may have increased.

Not C.