Question

Hector carried out an experiment to see if adding calcium powder to soil made plants grow taller. He took two potted plants and put calcium powder into only one of the pots. He gave each plant the same amount of sunlight and water and measured their growth after five weeks.
Based on his results, Hector claimed that calcium powder makes plants grow faster.

Which best describes his claim?

It is valid because his experiment had clear variables.
It is invalid because his sample size is small.
It is invalid because his claim is not based in science.
It is valid because he is an expert in his field.

Answer 1

It is invalid because his sample size is small.

With only one treated and one control plant, the result could be due to chance or unmeasured differences; you need replication (many plants) and repeated trials to support a general claim.