Question

which of the following is a valid criticism of investigation d? an observational study needs a response variable. a controlled experiment needs a response variable. an observational study needs a control group. a controlled experiment needs a control group.

Explanation:

Observational studies do not require a control group as they merely observe and record data without intervention. Controlled experiments need both a response variable and a control group for comparison to determine the effect of an independent - variable. Criticizing an observational study for lacking a control group is valid as it misinterprets the nature of observational studies.

Answer:

An observational study needs a control group.