Doctor friends have jokingly warned me, "Don't get sick on the Fourth of July." At many teaching hospitals, that's around the time new interns and residents arrive.

While the so-called July Phenomenon is perenially up for debate, more and more studies are coming out that strongly suggest timing does influence the kind of hospital care you get.

One study has found higher mortality rates among infants admitted to neonatal intensive care units at night. Another saw worse survival rates among heart attack patients admitted to New Jersey hospitals on the weekend.

Now a new study, published in the Journal of the American Medical Association, shows that hospital patients whose heart suddenly stops beating after 11 p.m. or on the weekend have a lower rate of survival than daytime or evening sufferers.

Researchers at Virginia Commonwealth University studied nearly 87,000 heart patients at more than 500 hospitals who had in-hospital cardiac arrests from January 2000 through February 2007.

Rates of survival a day after the cardiac arrest were higher for the daytime/evening sufferers than nighttime sufferers – 35 percent versus 29 percent – and neurological outcomes were more favorable – 15 percent to 11 percent.

The researchers said the discrepancy could have to do with hospital staffing and training.