individual variation within cultural groups, these differences can generally be seen in the life patterns of men and women today.

The life development pattern for men in early and middle adulthood is primarily focused on career achievement, with parenting generally relegated to a secondary role. After the attainment of career goals in mid-life, men's primary focus is thought to shift away from career issues and toward the enrichment of relationships with family and community.

Conversely, in early adulthood, the lives of women revolve primarily around their parenting responsibilities, which often take precedence over their career aspirations. Contrary to popular belief, studies of women with an "empty nest" suggest that women experience mid-life differently than men. Free from the parenting responsibilities of small children, women at mid-life are finally free to satisfy their individual needs for achievement by focusing their energies on their own career aspirations. Thus, the life pattern of women and men at early and middle adulthood appears to be remarkably different.

Scientific evidence and clinical experience suggest that there may be significant differences in the recruitment and retention of male and female subjects. For example, as the primary caretaker of children, a young woman with a family may be hesitant to enroll in a study that presents potential risks to her safety and livelihood, and ultimately that of her children. A working mother may also be hesitant to participate because she may be unable to incorporate the behavioral requirements of the study into her daily schedule in which she already experiences stress from conflicting role demands.

For example, a young mother may wish to reserve her annual or sick leave for the days when her children are ill, rather than a half or whole day of study-related health assessments. Women who agree to participate in a study may also experience some life crises in her family, such as a serious illness of a child, that may limit her short- and long-term ability to conform to the requirements of a study protocol.

There are also generational differences among women that are important to acknowledge. For example, women over the age of 65—who did not grow up in the era of self-help, preventive medicine, or communal exercise such as aerobic dancing—may be less willing to participate in studies that conflict with their prevailing beliefs about health. These beliefs may include such ideas as not taking hormone replacement because they feel well and believe that "if it's not broken, don't fix it"; or not participating in a study involving group exercise because they feel uncomfortable undressing and exercising with strangers. Women in this age group also may be unwilling to agree to participate in a study without discussing the study with their spouse or family.