Answer:
randomization creates validity in research experiments
Step-by-step explanation:
According to the information provided within the question it seems that the most important reason for this is that randomization creates validity in research experiments. By making the assignments random you increase the odds of creating two groups of 30 families that are as similar to each other as possible, thus drastically increasing the odds that the detergent is the only different variable in all the families of each group. Therefore increasing the validity of the results.