A student is writing about language in a sample of regional water contracts. Student notes: • Researchers sampled forty contracts from 1900 and forty from 1950. • The phrase common use appeared in 72% of the 1900 contracts and 21% of the 1950 contracts. • Individual allotment appeared in 8% of the 1900 contracts and 63% of the 1950 contracts. • The study did not investigate why the wording changed. • Contract lengths varied. The student wants to describe the shift without claiming a cause the study did not examine. Which choice best accomplishes this goal?