Final Report on the Effects of Sample Attrition on Estimates of Channeling's Impacts. APPENDIX


The probit models of sample inclusion used in this analysis (Equation (2) in Chapter III) expressed the probability of response as a function of screen characteristics. Similarly, the outcome equation used to estimate channeling impacts specifies that outcomes are affected by a set of auxiliary control variables, some of which are obtained from the baseline and others from the screen. These two set of variables are listed in the text. It is desirable for statistical reasons to have, in addition to common determinants of attrition and a given outcome, some factors that affect only the probability of attrition.

Table A.1 gives a list of the control variables used in the sample inclusion and outcome equations, and their source. An "S" indicates that the screen was the primary source, while a "B" indicates that the Baseline interview was the primary source. Model and site were available from research sample records maintained on all sample members and are denoted by an "R" in the table.

In a few cases, these variables have the same label in the table, but were in fact constructed somewhat differently for use in the two types of equations. For the outcome equations, the Medicaid coverage variable was defined to include three categories: currently covered under Medicaid, potentially covered within three months, and not likely to be covered within three months. Coverage was determined using information on current Medicaid coverage, income, and assets obtained from the baseline. The Medicaid coverage variable used in the attrition model was simply the answer to the question, asked at the screen, of whether the sample member was currently covered by Medicaid. For two other variables minor differences existed in variable construction. First, "proxy use" in the outcome model included an additional category for mixed self/proxy response, and referred to proxy use at the baseline rather than the screen. Second, "living arrangement/informal support" was defined differently in the two models. The variable used in the response model was screen data on whether sample members lived alone, with a child, with their spouse, or with others. The auxiliary control variable used in the outcome equation divided those living alone into those who were either receiving informal support or had a child living within a 30 minute travel radius and those who had no such evidence of available support. It also combined those living with a spouse and those living with others into a single category.

TABLE A.1: List of Control Variables Used in the Outcome and Attrition Model and Their Source
Outcome Variable Sourcea
  For Outcome  
  For Attrition  
Marital Status B -
Home Ownership B -
Life Satisfaction B -
Stressful Life Events Within Past Year B -
Number of Physician Visits Past 2 Months B -
Number of Hours per Week Formal Caregiver Spends in Residence B -
Formal Care B -
Number of Hours per Week Visiting Informal Caregiver Spends in Residence B -
Model R R
Site R R
Impairment on Activities of Daily Living S S
Continence S S
Medicaid Coverageb B S
Living Arrangement/Availability of Informal Supportb B S
Waitlisted/Applied for Nursing Home B S
Cognitive Impairment S S
Interviewer Assessed Unmet Need S S
In Hospital or Nursing Home at or Prior to Screen S S
Age in Years B S
Ethnic Background S S
Whether Proxy Respondentb B S
Sex B S
Whether Regular Helpc Received with Meal, Preparation, Housework, Shopping, Taking Medicine, Treatments at Home or Personal Care - S
Incomed - S
Number of Missing Items on Screen - S
Whether will need help to Complete Baseline - S
Number of Contacts to Obtain Screen Interview - S
  1. B indicates that the baseline interview is the primary source for this variable.
    S indicates that the screen interview is the primary source for this variable.
    R indicates that the research records are the primary source for this variable.
  2. These variables are defined somewhat differently in the two models. For an explanation of these differences, see text.
  3. Information on help received is captured in the formal and informal care baseline variables used in the outcome equation.
  4. Information on income is incorporated in the Medicaid coverage variable used in the outcome model.

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