National probability samples in studies of low-prevalence diseases. Part I: Perspectives and lessons from the HIV cost and services utilization study.

OBJECTIVE: To examine the trade-offs inherent in selecting a sample design for a national study of care for an uncommon disease, and the adaptations, opportunities and costs associated with the choice of national probability sampling in a study of HIV/AIDS. SETTING: A consortium of public and private funders, research organizations, community advocates, and local providers assembled to design and execute the study. DESIGN: Data collected by providers or collected for administrative purposes are limited by selectivity and concerns about validity. In studies based on convenience sampling, generalizability is uncertain. Multistage probability sampling through households may not produce sufficient cases of diseases that are not highly prevalent. In such cases, an attractive alternative design is multistage probability sampling through sites of care, in which all persons in the reference population have some chance of random selection through their medical providers, and in which included subjects are selected with known probability. DATA COLLECTION AND PRINCIPAL FINDINGS: Multistage national probability sampling through providers supplies uniquely valuable information, but will not represent populations not receiving medical care and may not provide sufficient cases in subpopulations of interest. Factors contributing to the substantial cost of such a design include the need to develop a sampling frame, the problems associated with recruitment of providers and subjects through medical providers, the need for buy-in from persons affected by the disease and their medical practitioners, as well as the need for a high participation rate. Broad representation from the national community of scholars with relevant expertise is desirable. Special problems are associated with organization of the research effort, with instrument development, and with data analysis and dissemination in such a consortium. CONCLUSIONS: Multistage probability sampling through providers can provide unbiased, nationally representative data on persons receiving regular medical care for uncommon diseases and can improve our ability to accurately study care and its outcomes for diseases such as HIV/AIDS. However, substantial costs and special circumstances are associated with the implementation of such efforts.

Variations in the care of HIV-infected adults in the United States: results from the HIV Cost and Services Utilization Study.

CONTEXT: Studies of selected populations suggest that not all persons infected with human immunodeficiency virus (HIV) receive adequate care. OBJECTIVE: To examine variations in the care received by a national sample representative of the adult US population infected with HIV. DESIGN: Cohort study that consisted of 3 interviews from January 1996 to January 1998 conducted by the HIV Cost and Services Utilization Consortium. PATIENTS AND SETTING: Multistage probability sample of 2864 respondents (68% of those targeted for sampling), who represent the 231400 persons at least 18 years old, with known HIV infection receiving medical care in the 48 contiguous United States in early 1996 in facilities other than emergency departments, the military, or prisons. The first follow-up consisted of 2466 respondents and the second had 2267 (65% of all surviving sampled subjects). MAIN OUTCOME MEASURES: Service utilization (<2 ambulatory visits, at least 1 emergency department visit that did not lead to hospitalization, at least 1 hospitalization) and medication utilization (receipt of antiretroviral therapy and prophylaxis against Pneumocystis carinii pneumonia). RESULTS: Inadequate HIV care was commonly reported at the time of interviews conducted from early 1996 to early 1997 but declined to varying degrees by late 1997. Twenty-three percent of patients initially and 15% of patients subsequently had emergency department visits that did not lead to hospitalization, 30% initially and 26% subsequently of those who had CD4 cell counts below 0.20 x 10(9)/L did not receive P carinii pneumonia prophylaxis, and 41% initially and 15% subsequently of those who had CD4 cell counts below 0.50 x 10(9)/L did not receive antiretroviral therapy (protease inhibitor or nonnucleoside reverse transcriptase inhibitor). Inferior patterns of care were seen for many of these measures in blacks and Latinos compared with whites, the uninsured and Medicaid-insured compared with the privately insured, women compared with men, and other risk and/or exposure groups compared with men who had sex with men even after CD4 cell count adjustment. With multivariate adjustment, many differences remained statistically significant. Even by early 1998, fewer blacks, women, and uninsured and Medicaid-insured persons had started taking antiretroviral medication (CD4 cell count adjusted P values <.001 to <.005). CONCLUSIONS: Access to care improved from 1996 to 1998 but remained suboptimal. Blacks, Latinos, women, the uninsured, and Medicaid-insured all had less desirable patterns of care. Strategies to ensure optimal care for patients with HIV requires identifying the causes of deficiency and addressing these important shortcomings in care.

The relationship between foliar nitrogen content and feeding by Odontota dorsalis Thun. on Robinia pseudoacacia L.

The relationship between total foliar nitrogen content and feeding by Odontota dorsalis Thun. on Black Locust trees (Robinia pseudoacacia L.) was examined via experimental manipulation of foliar nitrogen levels. Trees with high concentrations of foliar nitrogen received more herbivory by adult O. dorsalis, but herbivory by larvae was independent of foliar nitrogen concentration. Late in the growing season, leaf abscission induced by herbivory tends to mask the dependence of herbivory by adults on foliar nitrogen concentration. The percentage of variation in herbivory attributable to foliar nitrogen concentration drops from 20% in June to 2% by August. These observations suggest that variation in the interaction between R. pseudoacacia and O. dorsalis is at least partially conditioned on variation in foliar nitrogen concentration.