Suppose the reference group for computing incidence rate ratios of mortality is the group with index scores of 0/1 (most isolated). How will the incident rate ratios for the other 3 social isolation groups relative to this reference group compare to 1?

a. All 3 incidence rate ratios will be greater than 1.

b. All 3 incidence rate ratios will be less than 1.

c. Some will be less than 1, and some will be greater than 1.