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PubMed1998

School performance in adolescent Jamaican girls: associations with health, social and behavioural characteristics, and risk factors for dropout.

Health, nutrition and behavioural determinants of school achievement, attendance and dropout were examined in 452 girls aged 13-14 years, randomly selected from grade 8 in nine schools in inner-city Kingston, Jamaica. Girls who were anaemic, sexually active or aggressive had worse achievement levels. Better achievement levels were associated with possession of school materials and access to reading material outside of school. Poor attendance, early sexual activity, and not living with both parents predicted school dropout in the subsequent year. Strategies to reduce anaemia, to improve sex education and reduce the levels of aggression may benefit school performance.

Achievement↗
PubMed1980

Sample sizes for long-term medical trial with time-dependent dropout and event rates.

A general model is formulated that allows for time-dependent dropout and event rates in the determination of sample sizes for long-term medical trials when a therapy group and a control group are to be compared. The need for time-dependent event (dropout) rate is illustrated by using the Framingham Heart Study Mortality data to estimate sample size for the NHLBI (National Heart, Lung, and Blood Institute) Multiple Risk Factor Intervention Trial (MRFIT). A further generalization of the model allows for participants who drop out of the control group (e.g., because of therapeutic measures prescribed by their own physicians) to return (or not return) to the control group at a later date. The question of unequal sample sizes for the therapy and the control groups is also discussed.

Clinical Trials as Topic↗
PubMed2006

Male amelogenin dropouts: phylogenetic context, origins and implications.

Several commercial PCR multiplex kits incorporate the amelogenin locus for the purpose of human gender identification. Consequently, erroneous results in the electropherogram profile of this locus can carry important forensic implications. In this study, dropout of the amelogenin Y allele was detected in 5 out of 77 phenotypically normal Kathmandu males using the AmpFlSTR Identifiler kit. A battery of male-specific markers including SNPs, STRs, STSs, and a minisatellite were amplified for the five amelogenin null samples in order to delineate the breakpoints of the deletions as well as assess the overall integrity of the Y-chromosome. This study represents the first to examine the haplogroup affiliation of the AMGY deletions. The analyses performed suggest a single origin for the five deletions as indicated by their allocation to a specific Y-haplogroup (J2b2-M241), related Y-STR haplotypes and identical regional localization of breakpoints. The age estimated from the microsatellite variation for the amelogenin deletions (if they are associated by descent) is approximately 6.5+/-3.3 ky, younger than the previously reported related age of the M241 haplogroup representatives (13-14 ky). Our data in combination with previous publications suggest a concentration of afflicted individuals in the Indian subcontinent, possibly as a result of common ancestry. The elevated incidence of the amelogenin dropout in these populations accentuates the need to utilize other loci for gender determination in order to obtain an accurate set of inclusion criteria in forensic casework.

Alleles↗
PubMed1995

Participation in an employee fitness program: determinants of high adherence, low adherence, and dropout.

This article presents the results of a study of the determinants of adherence level in an employee fitness program. Of all 236 employees who started participating in the program the determinants of level of participation (high adherence, low adherence, and dropouts) during the program were studied by means of a pretest and posttest design. The questionnaire was based on different theoretical concepts. The determinants measured included the attitude toward an employee fitness program, self-efficacy expectation, and social support. The results show that there were no differences in determinants between the groups at the start of the program. During the second measurement the high- and low-adherence groups were most convinced of the benefits of participation in the program. The low-adherence group and the dropouts were least convinced of their ability to participate in a fitness program. Theoretical and practical implications are discussed.

Analysis of Variance↗
PubMed1999

Numerical statistics of power dropouts based on the Lang-Kobayashi model.

The statistics of power dropouts in semiconductor lasers subjected to delayed optical feedback have been numerically investigated using the Lang-Kobayashi model. The data from the numerical simulations have then been used to calculate the probability distribution functions, mean values, and return maps of the time that elapses between dropouts. In addition, the transition from the "low frequency fluctuation" to the "coherence collapse" regime has also been investigated. The numerical simulations compare well with both experimental results, obtained from multilongitudinal mode lasers, and analytical results obtained from other theoretical models. Evidence of "excitability" within the Lang-Kobayashi model is also reported.

Journal Article↗
PubMed2002

Stochastic entrainment of optical power dropouts.

We show that the natural pulsed behavior, in the form of sudden power dropouts, exhibited by semiconductor lasers subject to optical feedback can be entrained by the joint action of external noise and weak periodic driving. These power dropouts, which in the absence of forcing do not occur periodically, acquire the periodicity of the harmonic driving for an optimal amount of external noise, in what constitutes a form of stochastic resonance. This phenomenon is analyzed by means of a generalized Lang-Kobayashi model with external nonwhite noise in the modulated pump current, in terms of both the temporal correlation and the amplitude of the noise.

Journal Article↗
PubMedDate not supplied

Lung function and symptoms among cotton workers and dropouts three years after the start of work.

A longitudinal study of cotton workers was undertaken to assess the presence of work-related medical effects. A cohort of 110 subjects was examined before starting work and one year later. Measurements of pulmonary function were made before and after the work shift. Airway responsiveness was measured using a methacholine challenge test. A questionnaire was used to determine work-related symptoms. The 60 workers who remained after three years experienced an over-shift drop in FEV1 and an increase in airway responsiveness that did not increase after the first year. The data from the dropout group (n = 50) before work and after one year were compared with those for the active workers. The dropout group had a higher prevalence of symptoms of chest tightness and nasal irritation after one year of work. Atopy was not more common in this group. The results suggest that leaving work was related to symptoms of airways inflammation but not to atopy.

Adult↗
PubMed2003

Web-based research: methodological variables' effects on dropout and sample characteristics.

Previous research has made a beginning in addressing the importance of methodological differences in Web-based research. The present paper presents four studies investigating whether sample type, financial incentives, time when personal information is requested, table design, and method of obtaining informed consent influence dropout and sample characteristics (both demographics and measured attitudes). Undergraduates were less likely to drop out than nonstudents, and nonstudents offered a financial incentive were less likely to drop out than those offered no incentive. Complex tables, tables that were too wide, requests for personal information on the first page, and the imposing of additional informed consent procedures each provoked early dropout. As was expected, nonstudents and those presented with complex tables showed more measurement error and attitude differences. Asking for personal information and imposing additional consent procedures affected the demographic makeup, raising challenges to external validity.

Adult↗
PubMed1992

Characteristics of women performing strength training: comparison of participants and dropouts.

The physiological, anthropometric, personality and lifestyle characteristics of 122 women volunteering for a seven-week program of heavy resistance weight training were studied relative to adherence rates. Initially, volunteers were above-average in body mass and grip strength, but were below-average in chest girth and bicristal diameter. They were also physically active and only 20% smoked. Regular (R) attenders (attendance greater than 80%; 72% of the sample) were physically smaller in terms of stature, mass, girths and dimensions, but had greater strength per kg of mass or LBM compared to participants classified as infrequent (I; 24-76%) and dropout (DO; less than 20%). Conversely, I and DO members were more likely to smoke, to smoke more heavily, to drink coffee and to not eat breakfast. Most dropouts quit during the first week; among volunteers who continued, differences in assigned training intensity had no effect on adherence. Adherence was also unrelated to strength gains, anthropometric adaptations, or injury.

Adolescent↗
PubMed1991

Testing for random dropouts in repeated measurement data.

Diggle (1989, Biometrics 45, 1255-1258) proposes a test for random dropouts in repeated measurement data when the experiment has a completely randomized design. It is argued here that logistic regression is a comparable but more flexible technique for studying the occurrence of dropouts.

Animals↗
PubMed1983

Perceived competence among interscholastic sport participants and dropouts.

This study was conducted to examine the relationship between perceived competence and length of involvement in sport for sport participants and their counterparts who discontinued involvement. The relationship between participants (n = 239) and dropouts (n = 43) in a number of school-sponsored sports, years of experience and gender on perceived physical competence was examined using Harter's (1979) Perceived Competence Scale for Children. Results indicated a significant but somewhat low relationship between length of participation experience and perceived physical competence. The findings also indicated that participants in school-sponsored sports were significantly higher in perceived physical competence than were dropouts, and males were significantly higher in perceived physical competence than females.

Adolescent↗
PubMed1997

Relationship of polymorphonuclear leukocytes to capillary dropout in the human diabetic choroid.

Capillary dropout is an initial event in diabetic retinopathy, but the etiology is unknown. Recent evidence suggests that similar events may occur in the diabetic choroid. We have developed a method to evaluate the relationship between the polymorphonuclear leukocytes (PMNs) and capillary dropout in the human diabetic choroid using alkaline phosphatase (APase) histochemistry to label blood vessels and nonspecific esterase activity to identify PMNs. The number and distribution of PMNs in diabetic and nondiabetic choroidal capillaries (choriocapillaris) were analyzed in the flat perspective and the tissue then flat embedded in glycol methacrylate for histological sectioning. The total number of PMNs was increased within the choriocapillaris in five diabetic eyes (170.9 +/- 12.9 PMNs/mm2 of choroid) compared with five nondiabetic eyes (84.2 +/- 16.9 PMNs/mm2; P < 0.001). PMNs were almost always within blood vessel lumens and not in interstitial tissue. In the diabetic choroid, increased numbers of PMNs were present in areas of choriocapillaris with pathological changes (loss in APase activity and choroidal neovascularization) compared with nonpathological choriocapillaris (205.1 +/- 46.9 PMNs/mm2 in pathological versus 152.3 +/- 23.4 PMNs/mm2 in nonpathological areas; P < 0.001). PMNs were often queued up within the lumens of capillaries, demonstrating loss in APase activity. We have observed an increased number of PMNs in diabetic choroid compared with control nondiabetic choroids, and PMNs in diabetic choroid were associated with loss in APase activity, which was related to loss in viable endothelial cells. The results suggest that PMNs contribute to vaso-occlusive processes and endothelial cell injury in the diabetic choroid.

Aged↗
PubMed2003

Analysis of outcome in retrieved dropout patients in a rivastigmine vs placebo, 26-week, Alzheimer disease trial.

BACKGROUND: Treatment with cholinesterase inhibitors improves cognition in patients with Alzheimer disease (AD). In studies designed with a washout period at the end of the study, after treatment with a cholinesterase inhibitor is discontinued, the cognitive benefits of therapy are no longer apparent following washout. The rivastigmine trials discussed in this article were not designed with a posttreatment washout period at the end of the study. Therefore, to evaluate the effect of discontinuing treatment, we analyzed the retrieved dropout (RDO) population. OBJECTIVE: To evaluate the change in cognition (at week 26 vs baseline) observed in patients from 3 large clinical trials of AD who prematurely discontinued treatment with placebo or rivastigmine. DESIGN AND METHODS: Eligible patients with AD (Mini-Mental State Examination [MMSE] score, 10-26, inclusive) were enrolled in 1 of three 26-week, double-blind, placebo-controlled studies (Novartis US Pivotal [dose-range] Trial, US fixed-dose study, and a Global Pivotal [dose-range] Trial) that compared rivastigmine therapy with placebo. Patients who discontinued study participation (for any reason) (considered to be the RDO population) were encouraged to return for their scheduled week 26 efficacy evaluations. Effects on cognition were assessed using the Alzheimer's Disease Assessment Scale-Cognitive subscale (ADAS-Cog). RESULTS: The results for the Novartis US Pivotal Trials and for the 3 studies combined (Novartis studies B352, B351, and B303) are reported. In the US pivotal trial, RDO patients in the 6- to 12-mg/d group had been not receiving the drug (to be called "off drug") for 102 (57.7) days (mean [SD]) compared with 68 (51.7) days in the RDO placebo group. In these RDO analyses, a statistically significantly greater worsening on the ADAS-Cog mean change score was observed in the placebo group (n = 17) compared with the rivastigmine 6- to 12-mg/d group (n = 33) at week 26 (MMSE score, -8.2 vs -3.0; P =.009). In the pooled studies, the mean (SD) number of days off treatment was 95 (52.0) days for the rivastigmine 6- to 12-mg/d group and 66 (52.7) days for the placebo group. The RDO analysis also showed a statistically significantly greater decline in cognitive function as measured by the ADAS-Cog mean change score in the placebo group (n = 38) compared with the rivastigmine 6- to 12-mg/d group (n = 88) at week 26 (MMSE score, -5.69 vs -2.5; P =.004). A significantly greater proportion of patients in the placebo group exhibited at least a 4-point and 7-point worsening in ADAS-Cog scores at week 26 compared with the rivastigmine 6- to 12-mg/d group in both the Novartis US Pivotal Trials (P =.007, P =.009) and the pooled studies (P =.002, P =.017). CONCLUSIONS: After discontinuation of therapy, rivastigmine-treated patients exhibited less deterioration in cognitive function compared with placebo-treated patients. The less severe worsening of cognition after withdrawal of treatment in patients previously treated with rivastigmine suggests an effect on disease progression.

Adult↗
PubMed1996

Effect of dropouts in a longitudinal study: an application of a repeated ordinal model.

An analysis is presented of a longitudinal study of fluvoxamine, an antidepressant drug, with ordinal responses, regressed on a combination of discrete and continuous covariates and with a substantial proportion of dropouts. Classical methods, such as weighted least squares (SAS procedure CATMOD) and logistic regression, are not suitable for the analysis of such data. Instead, we illustrate how a recently introduced model can be used to solve most of the problems posed. The method is likelihood-based and is an extension of the bivariate Dale model to an arbitrary number of outcomes. The method is suitable for several types of designs commonly employed in clinical trials.

Antidepressive Agents, Second-Generation↗
PubMedDate not supplied

Cardiac rehabilitation programs and the problem of patient dropout.

As one of the leading causes of death in the United States, coronary atherosclerotic heart disease (CAHD) has been shown to have a reduced incidence if the principles of primary prevention are instituted to reduce cardiac risk factors. In people who already suffer from CAHD, employing secondary prevention such as controlling hypertension, reducing serum lipid levels, eliminating nicotine intake, reducing stress, losing weight, and increasing exercise habits can decrease recurrence of problems related to CAHD. Cardiac rehabilitation programs are a way to help CAHD patients restore optimal medical, physiological, psychological, social, and vocational performance following an acute cardiac event. A major problem in cardiac rehabilitation programs is patient dropout. For any cardiac rehabilitation program to be a success, the CAHD patient must become invested in the maintenance of health and, therefore, committed to participation in the program. The author reviews the current literature, including discussions of the history of cardiac rehabilitation, current trends in cardiac rehabilitation programs, factors that influence patients' investment in these programs, and ways in which the cardiac rehabilitation nurse might intervene to make an impact on patients' participation.

Coronary Disease↗
PubMed2006

A two-stage analysis of repeated measurements with dropouts and/or intermittent missing data.

This article is about a simple two-stage analysis that utilizes slope coefficients as the dependent variable for testing the significance of difference in mean rates of change in repeated measurement designs with missing data. The ANCOVA test on the doubly weighted slope coefficients provides power comparable to that of more complex maximum likelihood procedures when data are missing completely at random, requires fewer assumptions and is more generally applicable under realistic nonrandom dropout conditions, and most importantly can be readily understood and explained by those who actually do most controlled clinical research.

Analysis of Variance↗
PubMed2005

Joint modelling of bivariate longitudinal data with informative dropout and left-censoring, with application to the evolution of CD4+ cell count and HIV RNA viral load in response to treatment of HIV infection.

Several methodological issues occur in the context of the longitudinal study of HIV markers evolution. Three of them are of particular importance: (i) correlation between CD4+ T lymphocytes (CD4+) and plasma HIV RNA; (ii) left-censoring of HIV RNA due to a lower quantification limit; (iii) and potential informative dropout. We propose a likelihood inference for a parametric joint model including a bivariate linear mixed model for the two markers and a lognormal survival model for the time to drop out. We apply the model to data from patients starting antiretroviral treatment in the CASCADE collaboration where all of the three issues needed to be addressed.

Anti-HIV Agents↗