Although there are a fair number of theories about the process of grief, there has been less in the way of actual scientific data about the normal course of grief. In 2007, Paul Maciejewski and colleagues published a study of 233 bereaved adults conducted over a twenty-four-month period. They administered measures of yearning, disbelief, anger, depression, and acceptance at three time points in the first two years after the loss. Their results showed that disbelief peaked soon after the death and then consistently declined afterward. Yearning, which was the most pronounced and long lasting of the negative emotional responses to loss, peaked at about four months. Anger peaked at about five months, and depression at about six months. Acceptance continuously grew throughout the mourning period.

Surprisingly, even from the start, acceptance was rated higher than all other grief reactions. The high levels of acceptance may be explained by the large percentage of people who were over 65 at the time of the loss and whose loved ones died after a long illness. Furthermore, the study only included people whose losses were due to natural causes. Presumably, younger people and those whose loved ones died due to unnatural causes may have more difficulty with accepting the loss. Although this study may not pertain to all types of losses, it does give a good sense of the typical grief reaction to the most common kinds of losses.