CHICAGO (Reuters) - The most common symptom of grief following the death of a loved one from natural causes is not depression, as has been thought, but rather yearning or pining, which can last up to 2 years after the death, a new study indicates.

The most characteristic feature of bereavement is "more about yearning and pining and missing the person -- a hunger for having them come back," said senior author Dr. Holly Prigerson, of the Dana-Farber Cancer Institute in Boston.

"The focus on depression is misguided," she said in an interview. Yearning "really dominates the psychological picture, (with a feeling) that a part of you is missing and that without this essential piece you won't be happy."

The previous belief was that depression was the predominant negative effect, but the new study showed that it is yearning, which peaks after 4 months. Depression, which can be a product of that sadness, peaks much later.

The study, published in this week's issue of the Journal of the American Medical Association, was based on interviews over 2 years with 233 people who had lost a loved one, most often a spouse, due to death from natural causes.

The findings confirmed the overall sequence of the "stage theory" of grief popularized by Dr. Elisabeth Kubler-Ross in the 1960s -- disbelief, yearning, anger, depression and acceptance.

But, equally important, the data provide a benchmark for how grief changes over time," Prigerson said. As a result, she said, those who help treat grief need to focus first on yearning.

Sudden deaths to due to trauma or other reasons -- which account for about 6 percent of all U.S. deaths -- may produce higher degrees of disbelief and anger and less acceptance than what was found in this study.

Regardless of how the data are analyzed, the study concluded, all of the negative responses are in decline by about 6 months. If it goes beyond 6 months, the bereaved survivor may have to be referred for treatment.