Longitudinal Zero-inflated Count Data with Random Effects to Model Instrumental Activities of Daily Living (IADLs)
*Ping Yao, Northern Illinois University
Keywords: Longitudinal; Zero- inflated Poisson; random effect; Instrumental Activities of daily Living (IADLs); old adults.
The instrumental activities of daily living (IADLs) are important index of physical functioning in older adult studies. Measuring IADL-s longitudinally can provide useful information for assessing functional independence among older adults, which can capture the dynamic changes of responses over time. These count outcomes with a large proportion of zeros are often collected in longitudinal studies. The study is motivated by the data from the Hispanic Established Population for Epidemiological Study of the Elderly (HEPESE), a four wave (seven years) longitudinal study of community-dwelling elderly Mexican-Americans. The outcome measure is number of difficulties with ten items of daily activities. There are excess zeros IADL-s observed during seven year follow-up. We present Zero-inflated Poisson (ZIP) and hurdle model with nonlinear time effects to evaluate IADLs in the context of excess zeros. We conduct a goodness-of-fit test for the Zero inflated Poisson (ZIP) and hurdle model with excess zeros in longitudinal studies.
Important Dates & Deadlines
- October 9 - 11, 2013