While it is not clear why older people were excluded from research in the past, conducting research on older people is more difficult than working with younger subjects. Surveys have shown that older people tend to be less willing than younger people to become research subjects. As noted earlier, they are likely to have multiple medical conditions and to be taking several medications, factors that may cause them to be excluded from research projects that are trying to study single illnesses and the unadulterated effects of single medications. Because of these factors, older people also have a higher attrition rate, necessitating larger numbers of older subjects when the study begins in order to compensate for dropouts over time. Impairments in vision, hearing, or cognition may make efforts to obtain informed consent and enroll older subjects more time consuming and labor intensive. These factors together may make research on older people more expensive to complete. For all of the above reasons, it is clear that under representation of older people in clinical research will remain a persistent challenge. Specific, targeted initiatives from funding agencies and clinical trial consortia, however, can facilitate important studies with adequate numbers of older subjects.