Tikhonov adaptively regularized gamma variate fitting to assess plasma clearance of inert renal markers

The Tk-GV model fits Gamma Variates (GV) to data by Tikhonov regularization (Tk) with shrinkage constant, λ, chosen to minimize the relative error in plasma clearance, CL (ml/min). Using 169Yb-DTPA and 99mTc-DTPA (n = 46, 8–9 samples, 5–240 min) bolus-dilution curves, results were obtained for fit methods: (1) Ordinary Least Squares (OLS) one and two exponential term (E1 and E2), (2) OLS-GV and (3) Tk-GV. Four tests examined the fit results for: (1) physicality of ranges of model parameters, (2) effects on parameter values when different data subsets are fit, (3) characterization of residuals, and (4) extrapolative error and agreement with published correction factors. Test 1 showed physical Tk-GV results, where OLS-GV fits sometimes-produced nonphysical CL. Test 2 showed the Tk-GV model produced good results with 4 or more samples drawn between 10 and 240 min. Test 3 showed that E1 and E2 failed goodness-of-fit testing whereas GV fits for t > 20 min were acceptably good. Test 4 showed CLTk-GV clearance values agreed with published CL corrections with the general result that CLE1 > CLE2 > CLTk-GV and finally that CLTk-GV were considerably more robust, precise and accurate than CLE2, and should replace the use of CLE2 for these renal markers

Friendship context matters: Examining the domain specificity of alcohol and depression socialization among adolescents

Contains fulltext : 102553.pdf (publisher's version ) (Open Access)Driven by existing socialization theories, this study describes specific friendship contexts in which peer influence of alcohol misuse and depressive symptoms occurs. In the fall and spring of the school year, surveys were administered to 704 Italian adolescents (53 % male, M (age) = 15.53) enrolled in Grades 9, 10 and 11. Different friendship contexts were distinguished based on two dimensions referring to the level (i.e., best friendships and friendship networks) and reciprocity (i.e., unilateral and reciprocal) of the relationships. Social network and dyadic analyses were applied in a complementary manner to estimate peer socialization effects across the different friendship contexts. Results showed that within friendship networks both male and female adolescents' alcohol misuse was affected by friends' alcohol misuse, regardless of whether the relationship was reciprocated or not. Conversely, peer socialization of depressive symptoms only emerged within very best friendship dyads of female adolescents. Findings suggest that the effects of peer socialization depend on the friendship context and specific types of behaviors. The theoretical and methodological implications of the findings are discussed.17 p