Medical cost trajectories and onsets of cancer and noncancer diseases in US elderly population

Abstract

Time trajectories of medical costs-associated with onset of twelve aging-related cancer and chronic noncancer diseases were analyzed using the National Long-Term Care Survey data linked to Medicare Service Use files. A special procedure for selecting individuals with onset of each disease was developed and used for identification of the date at disease onset. Medical cost trajectories were found to be represented by a parametric model with four easily interpretable parameters reflecting: (i) prediagnosis cost (associated with initial comorbidity), (ii) cost of the disease onset, (iii) population recovery representing reduction of the medical expenses associated with a disease since diagnosis was made, and (iv) acquired comorbidity representing the difference between post- and pre diagnosis medical cost levels. These parameters were evaluated for the entire US population as well as for the subpopulation conditional on age, disability and comorbidity states, and survival (2.5 years after the date of onset). The developed approach results in a family of new forecasting models with covariates.

Figure 1

Empirical estimates (dots) and model predictions (solid lines) of cost per month per capita. The diseases are ordered according to the cost of onset. Values in the right upper corners of all plots are X ² per degree of freedom calculated as df ⁻¹∑_i=20 ²⁰(C _i − C(m))²/σ _i ², where C _i and σ _i are estimated mean and standard error of medical cost per month (for presentation purposes they were aggregated into two-month groups); df denoted the degree of freedom calculated as the difference between the number of measured points (41) and the number of estimated parameters (4). Note that the scale of the vertical axes is not the same for different rows of plots.

Figure 2

Schematic representation of the pattern of cost per month per capita and the notations for parameters estimated in the four plots below (Figure 3) using dynamic model of changes in medical costs accompanying the onset of chronic disease.

Figure 3

The model parameters (as sketched in Figure 2) were estimated within the 20-month period before and after onset of each of the 12 chronic conditions: (a) cost of initial comorbidity in U.S. dollars, that is, the mean cost per month per capita before onset, (b) cost of onset in U.S. dollars, that is, the mean expenditures in the month of onset, (c) population recovery rate in 1/month, that is, the speed of approaching new steady-state in medical expenditures, and (d) cost of acquired comorbidity in U.S. dollars, that is, an excess in expenditures in a new steady-state compared to those before disease onset. Horizontal bars denote the standard errors of parameter estimates obtained using the nonlinear least squares.