Answer:
Applying the scientific method by having two control groups.
Step-by-step explanation:
MargaretĀ“s design supports its conclusion because she applied the scientific method.
Margaret had two control groups: the ones that play videogames only a little and the ones who play a longer time.
She tested both groups and made an estadistic manner to show the results.
By this way she supported her conclusion.
If something she did wrong id that she didnĀ“t had an hipothesis to base of.