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Peter N. Le Souëf - One of the best experts on this subject based on the ideXlab platform.
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is Patient Dropout from a longitudinal study of lung function predictable and reversible
Pediatric Pulmonology, 2003Co-Authors: Stephen W. Turner, Peter N. Le SouëfAbstract:Predictive factors for individuals dropping out from a longitudinal study of lung function have not been described, nor have methods for re-recruiting Dropouts been developed. Our aims were to identify factors predictive of Dropout and methods of re-recruiting Dropouts from a longitudinal study of lung function. Details at enrollment into a longitudinal birth cohort study were compared between those who dropped out and those who were assessed 6 and 11 years later. Strategies for identifying individuals successfully contacted at 11 but not 6 years were described. Of 253 infants enrolled prenatally, 123 (49%) were followed up at age 6 and 194 (77%) at age 11 years. At 6 years, independent risk factors for a child dropping out were: no other sibling enrolled (OR, 4.0; 95% CI, 1.6, 10.1; P = 0.003); being first-born (OR, 2.8; 95% CI, 1.5, 5.2; P = 0.001); mother completing education at age 15 years (OR, 2.5; 95% CI, 1.3, 4.9; P = 0.007); and mother born overseas (OR, 2.3; 95% CI; 2.8; P = 0.01). The following were predictive of a child dropping out at 11 years: mother born overseas (OR, 4.8; 95% CI, 2.2, 10.2; P < 0.001); paternal smoker (OR, 3.1; 95% CI, 1.5, 6.5; P = 0.003); no other sibling enrolled (OR, 4.1; 95% CI, 1.1, 15.7; P = 0.04); and being first-born (OR, 2.1; 95% CI, 1.0, 4.3; P < 0.05). Of the 74 families successfully followed up at 11 but not 6 years, 35 (47%) were contacted by using data already held in study records, and 32 (43%) were contacted by databases available to the public. In conclusion, factors present at enrollment and predictive of Dropout from a longitudinal cohort study can be identified. Using a variety of methods, re-recruitment is possible for many individuals who previously dropped out. Pediatr Pulmonol. 2003; 35:29–33. © 2003 Wiley-Liss, Inc.
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Is Patient Dropout from a longitudinal study of lung function predictable and reversible
Pediatric pulmonology, 2002Co-Authors: Stephen W. Turner, Peter N. Le SouëfAbstract:Predictive factors for individuals dropping out from a longitudinal study of lung function have not been described, nor have methods for re-recruiting Dropouts been developed. Our aims were to identify factors predictive of Dropout and methods of re-recruiting Dropouts from a longitudinal study of lung function. Details at enrollment into a longitudinal birth cohort study were compared between those who dropped out and those who were assessed 6 and 11 years later. Strategies for identifying individuals successfully contacted at 11 but not 6 years were described. Of 253 infants enrolled prenatally, 123 (49%) were followed up at age 6 and 194 (77%) at age 11 years. At 6 years, independent risk factors for a child dropping out were: no other sibling enrolled (OR, 4.0; 95% CI, 1.6, 10.1; P = 0.003); being first-born (OR, 2.8; 95% CI, 1.5, 5.2; P = 0.001); mother completing education at age 15 years (OR, 2.5; 95% CI, 1.3, 4.9; P = 0.007); and mother born overseas (OR, 2.3; 95% CI; 2.8; P = 0.01). The following were predictive of a child dropping out at 11 years: mother born overseas (OR, 4.8; 95% CI, 2.2, 10.2; P
Madhukar Misra - One of the best experts on this subject based on the ideXlab platform.
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Effect of cause and time of Dropout on the residual GFR: A comparative analysis of the decline of GFR on dialysis
Kidney International, 2001Co-Authors: Madhukar Misra, Ed Vonesh, Harold L Moore, John C. Van Stone, Barbara F. Prowant, Karl D. NolphAbstract:low glomerular filtration rate (GFR) are purposefully switched to HD. If true, transferring CAPD Patients with low GFR to HD could create a selection bias that very well may account for the differences in GFR between PD and HD. This is particu- A natural progression of the disease process in Patients larly problematic if one then censors Patients at the time of with chronic renal failure often leads to an inexorable transfer from PD to HD from analysis (that is, Patients are no decline in residual renal function (RRF), eventually leadlonger followed in the study once they have switched treatment modalities). When this occurs, the data are said to be informa- ing to either dialysis or transplantation. A residual renal tively censored, a term used by statisticians to describe any creatinine clearance (CCr) of 1 mL/min translates into a kind of systematic bias associated with censored or incomplete weekly CCr of 10 L. It is obvious that the contribution data. In particular, informative censoring occurs when Patients of RRF to overall small solute and water clearance is who die or transfer to another modality very early have an important during the initial years of dialysis, both in associated lower starting GFR or higher rate of decline of GFR achieving adequacy targets and maintaining appropriate than Patients who either complete the study or who die or transfer much later. If Patient Dropout is indeed related to the rate fluid balance. Regardless of the mode of dialysis, that of decline in GFR and if this relationship differs between PD is, hemodialysis (HD) or peritoneal dialysis (PD), there and HD but is ignored in the analysis, then the results of such is usually an exponential decline in RRF with time. analysis may be biased. There have been many reports dealing with the preserMethods. This article analyzes the decline in GFR among
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preservation of glomerular filtration rate on dialysis when adjusted for Patient Dropout
Kidney International, 2000Co-Authors: Madhukar Misra, Ed Vonesh, David N Churchill, Harold L MooreAbstract:Preservation of glomerular filtration rate on dialysis when adjusted for Patient Dropout. Background Residual renal function (RRF) plays an important role in dialysis Patients. Studies in Patients on maintenance dialysis suggest that RRF is better preserved in Patients receiving peritoneal dialysis (PD) vis-a-vis those receiving hemodialysis (HD). We speculated that regardless of the Patient's type of therapy, the estimate obtained for the rate of decline in glomerular filtration rate (GFR) may be biased because of informative censoring associated with Patient Dropout. Informative censoring occurs when Patients who die or transfer to another modality very early have associated with them a lower starting GFR or a higher rate of decline of GFR than Patients who either complete the study or who die or transfer much later. If Patient Dropout is indeed related to the rate of decline in GFR and if this relationship is ignored in the analysis, then the estimate obtained of the rate of decline in GFR may be biased. Methods In an attempt to determine if there is a relationship between Patient Dropout and the decline in GFR, we reanalyzed the CANUSA data by modeling GFR as a nonlinear function of time with the rate of decline being exponential. Results This article highlights the significance of "informative censoring" when studying the decline of RRF on dialysis. The results show that for the CANUSA cohort, the mean initial GFR was significantly lower, and the rate of decline was significantly higher for Patients who died or transferred to HD than for Patients who were randomly censored or received a transplant. It is important to emphasize that the impact of informative censoring on previous analyses of the decline of RRF between PD versus HD is presently unclear. If bias caused by informative censoring is the same regardless of what therapy a Patient is on, then conclusions from previous studies comparing the decline in GFR between PD and HD would still be valid. However, if the magnitude of the bias differs according to therapy, then additional adjustments would be needed to fairly compare the decline in GFR between PD and HD. Because this analysis is restricted to Patients on PD, it would be scientifically incorrect to interpret previous studies solely on the basis of the results from this analysis. Conclusion In any longitudinal study designed to estimate trends in an outcome measured over time, it is important that the analysis of the data takes into account any effect Patient Dropout may have on the estimated trend. This analysis demonstrates that among PD Patients, both the starting GFR and the rate of decline in GFR are associated with Patient Dropout. Consequently, future studies aimed at estimating the rate of decline in GFR among PD Patients should also account for any dependencies between Dropout and GFR. Similarly, data analyzing for apparent differences in the rate of decline of GFR between PD and HD should also adjust for possible informative censoring.
Evan J.c. Lee - One of the best experts on this subject based on the ideXlab platform.
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A prospective randomized comparison of the Swan neck, coiled, and straight Tenckhoff catheters in Patients on CAPD
Peritoneal Dialysis International: Journal of the International Society for Peritoneal Dialysis, 1996Co-Authors: W.-c. Lye, N.-w. Kour, J. C. Van Der Straaten, S.-o. Leong, Evan J.c. LeeAbstract:Our objective was to study the impact of peritoneal catheter configuration on continuous ambulatory peritoneal dialysis (CAPO)-related infections, mechanical complications, and Patient Dropout in a...
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A prospective randomized comparison of the Swan neck, coiled, and straight Tenckhoff catheters in Patients on CAPD.
Peritoneal dialysis international : journal of the International Society for Peritoneal Dialysis, 1996Co-Authors: W.-c. Lye, N.-w. Kour, J. C. Van Der Straaten, S.-o. Leong, Evan J.c. LeeAbstract:Our objective was to study the impact of peritoneal catheter configuration on continuous ambulatory peritoneal dialysis (CAPD)-related infections, mechanical complications, and Patient Dropout in a prospective randomized trial. Forty consecutive Patients who were commencing CAPD were randomized to receive either a double-cuff, Swan neck coiled catheter or a double-cuff, straight Tenckhoff catheter, implanted by surgical technique. There was no significant difference in the peritonitis rate between the two groups. There was a lower rate of exit-site infection in the Swan neck group compared to the straight catheter group (0.29 vs 0.60 episodes/Patient-year, p < 0.05). Catheter-tip migration occurred in 3 Patients with the straight catheters compared to one Patient with the Swan neck catheter. No Patient had to discontinue CAPD because of mechanical complications. The number of CAPD Patient Dropouts was not significantly different between the two groups. The Swan neck configuration resulted in a significant reduction in the rate of exit-site infections. The coiled component of the catheter may lead to fewer episodes of catheter-tip migration. However, catheter configuration did not influence the number of technique failures.
Robert F. Meenan - One of the best experts on this subject based on the ideXlab platform.
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Secular changes in published clinical trials of second-line agents in rheumatoid arthritis.
Arthritis and rheumatism, 1991Co-Authors: Jennifer J. Anderson, David T. Felson, Robert F. MeenanAbstract:The present investigation was undertaken to explore changes over time in the design and reporting of trials of second-line drugs in rheumatoid arthritis, in the characteristics of Patients included in the trials, and in the sources of funding. We studied 105 trials of second-line agents for the treatment of rheumatoid arthritis, including placebo-controlled and comparative trials involving 8 different agents. Three time periods, 1945-1969, 1970-1979, and 1980-1989, were compared. We found little change in the standards for reporting on the design of trials or for reporting information on Patient Dropout and drug side effects, some increase in the complexity of the statistical methods used, but no increase in the use of power analysis (reported in only 13% of trials). The average age of Patients in clinical trials has increased. In recent years, there has been a substantial shift from placebo-controlled to comparative trials, and it is increasingly common for trials to be financially supported by pharmaceutical companies. The possible effects of secular trends should be considered when combining or comparing results of trials conducted in different years.
Vladimir V. Anisimov - One of the best experts on this subject based on the ideXlab platform.
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Effects of unstratified and centre‐stratified randomization in multi‐centre clinical trials
Pharmaceutical statistics, 2011Co-Authors: Vladimir V. AnisimovAbstract:This paper deals with the analysis of randomization effects in multi-centre clinical trials. The two randomization schemes most often used in clinical trials are considered: unstratified and centre-stratified block-permuted randomization. The prediction of the number of Patients randomized to different treatment arms in different regions during the recruitment period accounting for the stochastic nature of the recruitment and effects of multiple centres is investigated. A new analytic approach using a Poisson-gamma Patient recruitment model (Patients arrive at different centres according to Poisson processes with rates sampled from a gamma distributed population) and its further extensions is proposed. Closed-form expressions for corresponding distributions of the predicted number of the Patients randomized in different regions are derived. In the case of two treatments, the properties of the total imbalance in the number of Patients on treatment arms caused by using centre-stratified randomization are investigated and for a large number of centres a normal approximation of imbalance is proved. The impact of imbalance on the power of the study is considered. It is shown that the loss of statistical power is practically negligible and can be compensated by a minor increase in sample size. The influence of Patient Dropout is also investigated. The impact of randomization on predicted drug supply overage is discussed.
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Impact of Stratified Randomization in Clinical Trials
Contributions to Statistics, 2010Co-Authors: Vladimir V. AnisimovAbstract:This paper deals with the analysis of randomization effects in clinical trials.The two randomization schemes most often used are considered: unstratified and stratified block-permuted randomization. A new analytic approach using a Poisson-gamma Patient recruitment model and its further extensions is proposed. The prediction of the number of Patients randomized in different strata to different treatment arms is considered. In the case of two treatments, the properties of the total imbalance in the number of Patients on treatment arms caused by using stratified randomization are investigated and for a large number of strata a normal approximation of imbalance is proved. The impact of imbalance on the power of the trial is considered. It is shown that the loss of statistical power is practically negligible and can be compensated by a minor increase in sample size. The influence of Patient Dropout is also investigated.