Estimating informal care inputs associated with EQ-5D for use in economic evaluation. 
This paper estimates informal care need using the health of the patient.  The results can be used to predict changes in informal care associated with changes in the health of the patient measured using EQ-5D. Data was used from a prospective survey of inpatients containing 59,512 complete responses across 44,494 individuals.  The number of days a friend or relative has needed to provide care or help with normal activities in the last 6 weeks was estimated using the health of the patient measured by EQ-5D, ICD chapter and other health and sociodemographic data.  A variety of different regression models were estimated that are appropriate for the distribution of the informal care dependent variable, which has large spikes at 0 (zero informal care) and 42 days (informal care every day).  The preferred model that most accurately predicts the distribution of the data is the zero-inflated negative binomial with variable inflation.  The results indicate that improving the health of the patient reduces informal care need.  The relationship between ICD chapter and informal care need is not as clear.  The preferred zero-inflated negative binomial with variable inflation model can be used to predict changes in informal care associated with changes in the health of the patient measured using EQ-5D and these results can be applied to existing datasets to inform economic evaluation.  Limitations include recall bias and response bias of the informal care data, and restrictions of the dataset to exclude some patient groups.