33 Observation versus experiment Researchers at the University of Pennsylvania found that patients who are divorced separated or widowed had approximately a 40 greater chance of dying or developing a new func tional disability in the first two years following cardiac surgery than their married peers The data included 1576 subjects who underwent cardiac surgery of which 65 were married 33 were divorced separated or widowed and 2 had never been married The find ings were reported to be statistically significant 25 a Without reading any further details of this study how do you know that this was an observational study b Suggest some variables that might differ between the subjects in the study who were married versus those who are divorced separated or widowed Are any of these possible confounding variables Explain c Summarize briefly the limitations of this study Despite these limitations explain why this study still furniches useful information in formulating a