This quantifies the risk of developing disease in a certain time period, and does not compare between exposed and non-exposed groups.

This measures the proportion of disease occurrence that can be attributed to a specific exposure. It does not provide a comparison between different populations.

Relative risk compares the risk of developing the disease in the exposed (the town) vs. the non-exposed (national average). This will give the researchers a measure of how much greater the risk of Vitamin D deficiency is in the town, compared to the national average.

This calculates the proportion of disease in the whole population that is due to the exposure. It does not directly compare the risk between two different populations.