Still, senators, you are not off the hook. Limited access to health care may not entirely account for the poor health and the early deaths of so many of your fellow Americans. But it accounts for a good chunk.

A study about equity in access to health care for 21 countries in 2000 revealed that the United States had the highest degree of inequity in doctor use, even higher than Mexico — which is both poorer and generally more inequitable.

And as noted in a 2003 study by the Institute of Medicine, insurance status, more than any other demographic or economic factor, determines the timeliness and quality of health care, if it is received at all.

It doesn’t require an advanced degree to figure out what limited access to a doctor can do to people’s health. A review of studies published this week in Annals of Internal Medicine reported that health insurance substantially raises people’s chances of survival. It improves the diagnosis and treatment of high blood pressure, significantly cutting mortality rates. It reduces death rates from breast cancer and trauma. Over all, the review concluded that health insurance reduces the chance of dying among adults 18 to 64 years old by between 3 and 29 percent.

Another assessment, published last week in The New England Journal of Medicine, found that access to health insurance increases screenings for cholesterol and cancer, raises the number of patients taking needed diabetes medication, reduces depression, and raises the number of low-income Americans who get timely surgery for colon cancer.

It said that expansions in three states of Medicaid, the federal health insurance for the poor whose rolls Republicans are prepared to trim by 15 million over a decade, were found to reduce mortality by 6 percent over five years, mostly by increasing low-income Americans’ access to treatment for things like H.I.V., heart disease, cancer and infections.