To estimate the monetary value of informal care to people with Alzheimer's disease (AD) in Spain and to identify the main determinants of the time of informal care. We used the Survey on Disabilities, Autonomy and Dependency carried out in Spain in 2008 to obtain information on disabled individuals with Alzheimer and their informal caregivers. Assessment of informal care time was performed using three different approaches: the proxy good method, the opportunity cost method and the contingent valuation method. A statistical multivariate analysis-an ordered probit model-was performed to study the determinants of informal care provided. The average number of required informal hours per year was 4,151. The cost per caregiver ranged from 31,839 to 52,760 euros under the proxy good method; it was estimated at 20,053 euros under the opportunity cost method; and it ranged between 18,680 and 29,057 euros under the contingent valuation method. The degree of dependency and the formal care services were the main variables that explained the variability of the informal time provided. When a person presents a very high level of dependency, the probability of receiving more than 100 h of informal care per week is 25.8 % higher than a non-dependent person with AD. Formal in-home care complements informal caregiving, while formal care outside the home replaces it. Informal care represents a high social cost in people with AD, regardless of the estimation method considered. A higher level of dependence is associated with more hours of informal care provided.
