Figure 9.4 is taken from a retrospective cohort study (1990–2005) to examine the effect of systolic and diastolic blood pressure achieved in the first year of treatment, on all‐cause mortality in...

Figure 9.4 is taken from a retrospective cohort study (1990–2005) to examine the effect of systolic and diastolic blood pressure achieved in the first year of treatment, on all‐cause mortality in patients newly diagnosed with type 2 diabetes, with and without established cardiovascular disease. (a) What does “retrospective” mean in this context? (b) What is the risk factor here? (c) What do the results seem to indicate about a possible relationship between the two variables?