A medical researcher experimented with the effects of calcium intake on the healing time of broken bones. People who had similar broken bone injuries were divided randomly into two groups, one of which received a calcium supplement and one of which received a placebo. The data showed that there was no significant difference in healing times between the two groups, so the researcher concluded that calcium intake has no effect on bone healing time. Why is the conclusion of the researcher not justified? The researcher did not use a control group.
The bone injuries in different people cannot be compared.
The overall calcium intake of the two groups was not considered.
The data can only give a statistical probability, so no conclusion can be made.