Hi,
These labels are referring to the specific types of data in the table; they are exposure category labels. Dose is referring to the arsenic exposure dose, which is given in the table as - "time-weighted water arsenic concentration" in the left column. These terms "dose" and "time-weighted" are referring to the specific exposures used in the study, not any special type of RERI.
Another way we could have phrased this was - "Please calculate the exposure stratum specific RERI, using the data in the table above, of which an excerpt has been provided below"
Please take another look at the table data labels and let us know if this clarifies things.
thanks,
JMC