Question 21·Hard·Evaluate Statistical Claims: Observational Studies and Experiments
A nutritionist designed an experiment to determine whether eating a new energy bar before work increases the number of units assembled per hour by factory workers. The nutritionist posted a sign-up sheet in the break room of a large factory, and 80 employees volunteered to participate. The volunteers were randomly assigned either to eat the energy bar before their shifts or to follow their usual routine. The nutritionist found that workers who ate the bar assembled significantly more units per hour than those who did not.
What is the largest group to which the results of this experiment can be appropriately generalized?
For SAT questions about generalizing results, first identify the sample (who actually participated) and how they were selected. Ask: Was this a random sample from a larger population, or a volunteer/convenience group? Random assignment lets you infer cause and effect within the sample, but only random sampling justifies generalizing to a broader group. Then scan the answer choices from largest to smallest group and select the largest group that is still clearly represented by the way the sample was chosen—often, this is just the participants themselves when volunteers were used.
Hints
Focus on who took part
Underline the description of who participated in the experiment. Ask yourself: Which group actually provided data in this study?
Think about how participants were chosen
Were the workers randomly selected from all possible factory workers, or did they choose to participate by signing up?
Connect selection to generalization
You can safely generalize results only to groups that the sample fairly represents. Which groups in the answer choices include people who did not volunteer?
Compare the sizes of the answer-choice groups
Among the answer choices, look for the largest group that you can confidently say matches how the participants were actually chosen and studied.
Step-by-step Explanation
Identify who was actually in the study
Read the description and note who participated: 80 employees at one factory who volunteered by signing up on a sheet in the break room. This group is called the sample of the study.
Understand the type of randomization used
The nutritionist randomly assigned the 80 volunteers to either eat the energy bar or follow their usual routine. Random assignment helps show that differences in output are caused by the energy bar (within this group), because it balances other factors between the two groups. However, random assignment is not the same as random sampling from a larger population.
Connect sampling to generalization
To generalize results to a larger group (like all workers at the factory or all factory workers in the city), the participants must be a random sample from that larger group. Here, the workers chose to volunteer, so they may be different from nonvolunteers (for example, more health-conscious or more motivated). Because of this, the sample does not represent all workers at the factory, the city, or at similar factories.
Choose the largest group that is definitely represented
Since only the volunteers were studied and they were not randomly selected from any larger group, the safest and largest group we can correctly generalize to is the exact group that participated in the study. Therefore, the correct answer is C) The 80 workers who volunteered for the study.