Question

coffee stations in offices often just ask users to leave money in a tray to pay for their coffee, but many people cheat. on some days, researchers at newcastle university replaced the picture of flowers on the wall behind the coffee station with a picture of staring eyes. they found that the average contribution increased significantly above the well - established standard when people felt they were being watched, even though the eyes were patently not real. complete parts a through c below.
a) was this a survey, an observational study, or an experiment?
this was an experiment because the researchers controlled the situation by determining which picture was used.
b) identify the variables.
the treatment is the picture that is displayed behind the coffee station. the response was the average contribution from the participants.
c) what does \increased significantly\ mean in a statistical sense?
a. the amount collected increased by at least 50%.
b. not enough was collected until the picture with the staring eyes was used.
c. the differences in money collected were larger than could be reasonably attributed to usual day - to - day variation.
d. the amount collected increased by at least 7%.

Explanation:

To determine the correct answer for "increased significantly" in a statistical sense, we analyze each option:

• Option A: A specific percentage (50%) is not the definition of statistical significance. Significance is about variability, not a fixed percentage increase. Eliminate A.
• Option B: "Not enough was collected" does not relate to the meaning of "increased significantly". Significance is about the difference relative to variability, not sample size adequacy here. Eliminate B.
• Option C: Statistical significance means that the observed difference (in money collected) is larger than what would be expected from normal day - to - day random variation. This matches the concept of significance.
• Option D: A specific percentage (7%) is not the definition of statistical significance. Significance is about variability, not a fixed percentage increase. Eliminate D.

Answer:

C. The differences in money collected were larger than could be reasonably attributed to usual day - to - day variation.