Half the plants, chosen at random, are given the new fertilizer. Runners who already train daily are compared with those who do not. One of those is an experiment and the other is not, and the difference is a single word.
Every question on these free printable worksheets is settled by asking one thing first: was anything DONE to anybody? If a researcher decided who got what, and decided it at random, it is an experiment — and that assignment is the only reason an experiment can claim one thing caused another. If nothing was assigned, the sentence is either asking people something, which is a sample survey, or measuring an outcome in groups that were already different, which is an observational study.
Why this sheet works
The order of those two questions is the point. Reaching for "observational" first is how a student calls a randomized trial an observation: nobody in the sentence looks like they are being experimented on, and the word "randomly" gets read as random SELECTION rather than random assignment. Assignment is checked before anything else, on every question and in the worked walk.
How this one works
One question from a sheet like this one, worked a step at a time — with a sentence saying what just happened and why.
Runners who already train daily are compared with those who do not.
Sample surveyExperimentObservational study
2
Two classes drawn at random use the new textbook; two keep the old.
Sample surveyExperimentObservational study
3
A cafe asks 80 randomly picked customers to rank four new dishes.
Sample surveyExperimentObservational study
4
Half the aisles, picked at random, get the brighter lighting.
Sample surveyExperimentObservational study
5
A town phones 500 households to ask about a new library.
Sample surveyExperimentObservational study
6
Test scores are compared for students who chose to join the club.
Sample surveyExperimentObservational study
Reading a study · Survey, experiment or studyAnswer key
1. Runners who already train daily are compared with those who do not. → Observational study — The groups were ALREADY different; nobody assigned the training.2. Two classes drawn at random use the new textbook; two keep the old. → Experiment — The classes did not choose — they were assigned at random: an experiment.3. A cafe asks 80 randomly picked customers to rank four new dishes. → Sample survey — Ranking on request is an opinion asked for: a sample survey.4. Half the aisles, picked at random, get the brighter lighting. → Experiment — The aisles were assigned their lighting at random: an experiment.5. A town phones 500 households to ask about a new library. → Sample survey — Questions to a sample, and no treatment given: a sample survey.6. Test scores are compared for students who chose to join the club. → Observational study — The students CHOSE, so this is measuring groups as they are.
