A Test of the Validity of Imputed Legal Immigration Status.

We evaluate the performance of a widely used technique for imputing the legal immigration status of U.S. immigrants in survey data-the logical imputation method. We validate this technique by implementing it in a nationally representative survey of U.S. farmworkers that includes a well-regarded measure of legal status. When using this measure as a benchmark, the imputation algorithm correctly identifies the legal status of 78% of farmworkers. Of all the variables included in the algorithm, we find that Medicaid participation poses the greatest challenge for accuracy. Using the American Community Survey, we show that increased Medicaid enrollments stemming from the implementation of the Affordable Care Act in 2014 led to sizable changes in the share of immigrants imputed as legal over time and across space. We explore the implications of these changes for two previous studies and conclude that including Medicaid criteria in the imputation algorithm can significantly impact research findings. We also provide tools to gauge the sensitivity of results.

The measurement of hemodialysis access blood flow by a conductivity step method.

BACKGROUND AND OBJECTIVES: Measurement of blood flow rate (Qa) is used to monitor dialysis access, AV fistulas, and grafts. Indicator dilution measurements of the recirculation (R) induced by reversal of hemodialysis blood lines are commonly used. This plus the dialysis circuit flow (Qb) allows calculation of Qa. R also changes the conductivity, which can be measured by a conductivity cell in the spent dialysate. The change in conductivity caused by line reversal should vary with Qa. A methodology for Qa measurement utilizing this conductivity step is proposed. This study compares conductivity step methodology against the reference method of ultrasound dilution (Qa-Trans). DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This was an open diagnostic test study in a single academic hospital setting involving 15 hemodialysis-dependent patients. Each was studied over four hemodialysis treatments. During each treatment, two pairs of Qa measurements (conductivity step and Trans) were made. Pre- and postdialysis sodium levels were also measured. RESULTS: Average Qa-conductivity step was 1040 ml/min. Average Qa-Trans was 1030 ml/min. The difference was NS. The data pairs showed mean difference of 1.3 +/- 17% (SD). The SD indicates a relatively large variation between data pairs. There was significant linear correlation between the Qa-conductivity step and Qa-Trans results (r = 0.91, P < 0.001). Serum sodium rose slightly but significantly over dialysis (P < 0.001). CONCLUSIONS: Qa measurement by conductivity step may be an acceptable alternative to ultrasound dilution methodology. Care must be taken to prevent salt loading when the conductivity step is used.