You are interested in researching the effects of vitamin c on colds. for your study, you round up a group of people, all roughly the same age and healthy. you give them all vitamin c pills to take every day and have them check in with you once a month to see if they get a cold. why is this not a good study design

the research study lacked a control group, It was  difficult to know individuals who are not taking  Vitamin C and exposed to cold

Explanation:

Normally in a research study there should  be a control group of the same age group like the study group in the same environment, who will not  Vit, C but a   placebo. To determine if Vitamin. C is   the  actual effective drug for prevention of cold  in the study group or other factors.

Therefore, in this study It was  difficult to know individuals who were not taking  Vitamin C and exposed to cold(control group) Because, it is the comparison of the  data from the control  group and the study groups  that is  needed to determine the efficacy of Vitamin C