I think that he can not show definitively that vitamins cause a person to be taller.
The study does show a relationship between the two, but it's not necessarily one of cause and effect. There could be other factors involved in the experiment.
The kids who received vitamins might have been receiving better nutrition and better care in general opposed to those who did not have any vitamins.
Also, maybe certain ethnic groups are just naturally shorter so they would be shorter with vitamins anyway.
Explanation: I hope this answers the question to some degree.
I'm sorry if it doesn't.
He can not show definitively that vitamins cause a person to be taller.
No relationship can be shown between vitamins and height
The experiments must contain larger sample sizes (N ≥ 200) in order to have statistically significant results which enable to establish causal associations. In this case, it is expected that the experimental results are the product of chance alone