A valid cause-and-effect design-that is, one with internal validity-rules out alternative explanations of results by comparing what happened with an intervention to what happened in the absence of the intervention.
They need to compare the use of intervention and without.
They do not take into account the effect of the intervention.
The bedroom is empty.
You heard the table fall, correct?
Something falls off from a balcony.
A few people are in a park
Trips to Catalina Island. one of California's eight Channel Islands. are most popular with the tourist.
The only game show that's on in the evening is Wheel of Fortune.