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PubMed2000

Dropouts in longitudinal studies: definitions and models.

The widely used distinction of Little and Rubin (1) about types of randomness for missing data presents difficulties in its application to dropouts in longitudinal repeated measurement studies. In its place, a new typology of randomness for dropouts is proposed that relies on using a survival model for the dropout process. In terms of a stochastic process, dropping out is a change of state. Then, the longitudinal measures and dropout processes can be modeled simultaneously, each conditional on the complete previous history of both repeated measures and states. In this context, Poisson regression is used to fit various proportional hazards models, some of which are new, to the dropout process using the longitudinal measurements responses as time-varying covariates. As examples of longitudinal measurement studies displaying nonrandom dropout processes, a dental study of testosterone production in rats and clinical trials for treatment of gallstones and of depression are analyzed.

Algorithms↗
PubMed1989

Early school dropout: configurations and determinants.

This longitudinal study examined behavioral, cognitive, and demographic factors associated with early school dropout. Follow-up assessments were completed on a sample of girls (n = 248) and boys (n = 227) who had first been seen when they were in the seventh grade. School status was determined for all living subjects; 99% of them were interviewed individually in the fifth annual test wave. Overall, 14% of the group had dropped out of school prior to completing grade 11. The clusters of males and females most vulnerable to early school dropout were characterized in grade 7 by high levels of aggressiveness and low levels of academic performance (82% early dropout in males; 47% early dropout in females). In seventh grade, subjects who subsequently dropped out tended to affiliate with persons who were also at risk for dropout. Socioeconomic status, race, and early parenthood were also associated with school dropout. The primary outcomes were supported by convergent variable-oriented and person-oriented analyses. Some developmental dynamics of the phenomena are discussed.

Achievement↗
PubMed2006

Dropout in a longitudinal, cohort study of urologic disease in community men.

BACKGROUND: Reasons for attrition in studies vary, but may be a major concern in long-term studies if those who drop out differ systematically from those who continue to participate. Factors associated with dropout were evaluated in a twelve-year community-based, prospective cohort study of urologic disease in men. METHODS: During 1989-1991, 2,115 randomly selected Caucasian men, ages 40-79 years from Olmsted County, Minnesota were enrolled and followed with questionnaires biennially; 332 men were added in follow-up. A random subset (approximately 25%) received a urologic examination. Baseline characteristics including age, benign prostatic hyperplasia (BPH) symptoms, comorbidities, and socioeconomic factors were compared between subjects who did and did not participate after the twelfth year of follow-up. RESULTS: Of the 2,447 men, 195 died and were excluded; 682 did not participate in 2002. Compared with men in the 40-49 year age group, men > or = 70 years of age at baseline had a greater relative odds of dropout, 2.65 (95% CI: 1.93, 3.63). In age-adjusted analyses, relative to men without stroke, men who had suffered a stroke had a higher odds of dropout, age-adjusted OR 3.07 (95% CI: 1.49, 6.33). Presence of at least one BPH symptom was not associated with dropout, (age-adjusted OR 1.12 (95% CI: 0.93, 1.36)). CONCLUSION: These results provide assurance that dropout was not related to primary study outcomes. However, factors associated with dropout should be taken into account in analyses where they may be potential confounders.

Adult↗
PubMed2005

The association between medication usage and dropout status among participants of an exercise study for people with osteoarthritis.

BACKGROUND AND PURPOSE: Little is known about predictors of dropout status in exercise studies for people with osteoarthritis. Losses to follow-up can pose serious threats to study validity. The purpose of this study was to assess the ability of arthritis medication usage the month prior to enrollment to predict dropout status among participants in an exercise study for people with osteoarthritis. SUBJECTS AND METHODS: Men and women who participated in an exercise study for people with osteoarthritis (N=143) were followed. Participants who completed 24+ months of the exercise program were considered retained, whereas individuals who withdrew prior to 24 months were considered dropouts. RESULTS: Of the 143 participants analyzed, 78 (55%) completed 24+ months of the exercise program and 65 (45%) dropped out. Among those who reported arthritis medication usage, 54% were lost to follow-up. The group reporting no usage of arthritis medication had a 20% dropout rate (odds ratio=3.5, 95% confidence interval=1.6-7.6). The final adjusted model controlling for baseline health status, body mass index, and the interaction between baseline health status and body mass index indicated that those individuals who reported arthritis medication usage were more than 4 times more likely to drop out than were those who reported no arthritis medication usage (odds ratio=4.5, 95% confidence interval=1.8-11.4). DISCUSSION AND CONCLUSION: The results showed that self-reported arthritis medication usage the month prior to study enrollment was associated with subsequent dropout status among this group of exercisers with osteoarthritis. Further identification of baseline characteristics predictive of participant dropout status may benefit future exercise studies. A priori knowledge of "at-risk" exercise study participants will afford the opportunity for the timely allocation of appropriate resources aimed at reducing losses to follow-up.

Aged↗
PubMed1992

Dropout--Mertonian or reproduction scheme?

This article reports on dropouts in four schools in Israel. Two main research questions were addressed: (1) Is it possible to identify a potential dropout through examination of his/her attitudes and competence before the actual act of leaving school? (2) Is there a difference between dropouts and persistent students in different educational settings (academic, vocational, agricultural, and comprehensive high schools)? Significant differences were found in the attitudes of persistent students and dropouts even before the act of dropping out occurred. In the vocational, comprehensive, and agricultural schools, the dropouts scored more positively on the self-estrangement, meaninglessness, and misfeasance scales. In the academic school, the dropouts scored positively on the anxiety scale. Results were interpreted in light of the Mertonian scheme of ends and means as well as the reproduction scheme. The Mertonian scheme was deemed more applicable.

Achievement↗
PubMed1989

Counseling male spouse abusers: characteristics of treatment completers and dropouts.

This article examines differential demographic and personality characteristics of completers (n = 88) and dropouts (n = 68) from a spouse abuse abatement counseling program. Chi-square analyses on categorical data and multivariate analyses of variance on personality test data revealed several predicted findings. In general, treatment dropouts were younger and had lower employment levels than treatment completers. Dropouts also had higher pretreatment levels of police contact than completers for alcohol- and drug-related offenses, as well as miscellaneous offenses, but not for violent offenses. Personality data indicated greater borderline and schizoidal tendencies among dropouts, compared to completers, as measured by the Millon Clinical Multixial Inventory (MCMI). Moreover, completers evidence lower levels of overall psychopathology than dropouts. Discriminant function analyses correctly predicted 71% of dropouts with the following variables: volunteer status, race, employment, MCMI-Alcohol scale and pretreatment miscellaneous criminal offenses. The results of the present study are discussed in terms of victim safety planning and program policy implications.

Follow-Up Studies↗
PubMed1986

School discrimination and the high school dropout: a case for adolescent advocacy.

The literature supports the theory that high school dropouts are unable to find employment when they leave school, and that girls who dropout are more likely than boys to return. It was hypothesized that schools may not want to take back students who had once dropped out of school. To investigate the schools' response to dropouts trying to return, three actors were used to portray a male dropout, a female dropout and a parent of a dropout. Fifteen schools were contacted, to determine the differences in response to each actor. The results indicate that schools were more likely to accept the child who is represented by the parent, and that schools reacted more favorably to the parent. The results are discussed and specific recommendations made for program and practice.

Adolescent↗
PubMed1988

The use of proportional hazards regression in investigating dropout rates in a longitudinal study.

One difficulty with the interpretation of data from longitudinal studies is the bias associated with those who do not complete the study. In a 12-month study on the occurrence of musculoskeletal problems in 966 runners (583 of whom completed the study), a proportional hazards model with time-dependent covariates was used to assess factors associated with dropout at the various stages of the study. This approach allowed examination of baseline factors as well as the effect of change in mileage, the occurrence of a musculoskeletal problem, or the occurrence of another health problem on the rate of dropout. Those most likely to drop out of the study were younger and heavier at baseline and, prior to drop out, were less likely to experience general health problems and more likely to show a 40% decline in weekly running mileage in the month before dropout. Examination of factors associated with dropout is important since factors influencing dropout may also affect the study outcome for the risk factor analysis (a musculoskeletal problem severe enough to be seen by a physician). The results of the dropout analysis can be used to guide in the choice of analytic methods and to aid in the interpretation of the risk factor analyses.

Adult↗
PubMed1999

Predictors of dropout and burnout in AIDS volunteers: a longitudinal study.

Burnout among HIV/AIDS volunteers contributes to the loss of dedicated personnel resulting in strain on the HIV/AIDS care system. Past research has suggested that there were significant stresses and burnout associated with AIDS caregiving. We investigated the predictors of dropout in AIDS volunteers over time, and specifically, which of the variables of the stressors and rewards of being a volunteer (collected at baseline) predicted who would drop out two years later. The volunteers were the subjects of Nesbitt et al. (1996), who were members of an interfaith religious-based organization in Houston, Texas. The subjects were re-contacted by mail after two years, and 76 of the 174 respondents completed a brief questionnaire which gave details of current volunteering activity, reasons for dropout (if they had dropped out) and completed the Texas Revised Inventory of Grief (TRIG). Forty dropped-out from volunteering while 36 continued. Data show the independent variables of total stressor score, the Maslach Burnout Inventory score of Depersonalization intensity and the three subscale scores involving stress: client problems and role ambiguity, emotional overload and organizational factors as being significant in predicting dropout in HIV/AIDS volunteers over time. The best predictors of the dropping-out of HIV/AIDS volunteers can be divided into the stresses (client problems and role ambiguity, emotional overload and organizational factors) and depersonalization intensity. The results showed that volunteers who experienced more client problems and role ambiguity, more emotional overload and more problems with organizational factors are more likely to drop out from the volunteer programme. They also show that the dropout volunteers have a significantly higher level of depersonalization intensity than the continuing volunteers, with the risk of dropout increasing by almost a third in the highest tertile of depersonalization intensity scores compared with those with lower scores. These data indicate that it is the stressors of AIDS volunteering, including the intensity of depersonalization, which lead to dropout, and that rewards do not appear to have a protective effect.

Acquired Immunodeficiency Syndrome↗
PubMed1990

The health belief model: predicting compliance and dropout in cardiac rehabilitation.

We investigated the health belief model and the health locus of control constructs as predictors of group membership (compliers or dropouts) with cardiac rehabilitation and whether they added predictive utility to routinely assessed patient demographics and health behaviors. Questionnaires were completed on entry into the study by 120 patients with coronary artery disease, and by the end of the 6 month program there were 58 compliers and 62 dropouts. Discriminant function analyses were carried out to determine prediction of group membership. The health belief model predicted group membership 64.6% of the time, explaining 5.2% of the variance. Demographics, health behaviors, and health belief model factors accounted for 21.1% of the variance between compliers and total dropouts with group membership correctly predicted 74.4% of the time; avoidable and unavoidable dropout was correctly predicted 84.2% of the time with 56.9% of the variance explained. Health locus of control did not distinguish between compliers and dropouts. The addition of the health belief model provided additional information about compliance with cardiac rehabilitation beyond that explained by demographic and health behavior variables alone, particularly when predicting avoidable/unavoidable dropout.

Attitude to Health↗
PubMed1998

Adjusting sample size for anticipated dropouts in clinical trials.

Statistical models for calculating sample sizes for controlled clinical trials often fail to take into account the negative impact that dropouts have on the power of intent-to-treat analyses. Empirically defined dropout correction coefficients are proposed to adjust sample sizes for endpoint analysis of variance (ANOVA) and analysis of covariance (ANCOVA) that have been initially calculated assuming complete data. The implications of type of analysis (change-score ANOVA or ANCOVA), correlational structure of the repeated measurements (compound symmetry or autoregressive), and percentage of dropouts (20% or 30%) are considered, together with other less influential design and data parameters. We recommend the use of ANCOVA to correct for baseline differences and for time-in-study if there is a nonspecific change across time. Given a realistic autoregressive (order 1) correlational structure for the repeated measurements and a proposed endpoint ANCOVA, the empirical results support the common practice of increasing calculated sample size by the anticipated number of dropouts. The previous rationale has been to retain a requisite number of "completers" on which to base statistical inferences. We believe the present results provide the first documentation of the relevance of that strategy for intent-to-treat analyses in which the incomplete data for dropouts must be included. Based on comparative power analyses, the strategy also seems appropriate for maintaining the power of mixed-model regression analyses, simple regression on a normalized time scale, and analyses of trends fitted to imputed scores for dropouts.

Clinical Trials as Topic↗
PubMed2005

The analysis of incomplete cost data due to dropout.

Incomplete data due to premature withdrawal (dropout) constitute a serious problem in prospective economic evaluations that has received only little attention to date. The aim of this simulation study was to investigate how standard methods for dealing with incomplete data perform when applied to cost data with various distributions and various types of dropout. Selected methods included the product-limit estimator of Lin et al. the expectation maximisation (EM-) algorithm, several types of multiple imputation (MI) and various simple methods like complete case analysis and mean imputation. Almost all methods were unbiased in the case of dropout completely at random (DCAR), but only the product-limit estimator, the EM-algorithm and the MI approaches provided adequate estimates of the standard error (SE). The best estimates of the mean and SE for dropout at random (DAR) were provided by the bootstrap EM-algorithm, MI regression and MI Monte Carlo Markov chain. These methods were able to deal with skewed cost data in combination with DAR and only became biased when costs also included the costs of expensive events. None of the methods were able to deal adequately with informative dropout. In conclusion, the EM-algorithm with bootstrap, MI regression and MI MCMC are robust to the multivariate normal assumption and are the preferred methods for the analysis of incomplete cost data when the assumption of DCAR is not justified.

Algorithms↗
PubMed1987

A multivariate analysis of dropout status by length of stay in a rural community mental health center.

Homogeneity and other characteristics of rural community mental health center adult, outpatient dropouts were investigated with particular attention to length of stay. Analyses of 93 cases during a one year period revealed that qualities of the therapist discriminated short-term dropouts from long-term dropouts and long-term terminators. The client's chronicity discriminated short-term dropouts from short-term terminators. Dropouts were not found to be a homogeneous group. While therapist characteristics may be important in predicting termination status in long-term stays, the termination status of short-term clients may be determined primarily by the severity of the client's problems and whether or not they have received previous treatment.

Adolescent↗
PubMed2003

Evaluation and characteristics of "dropouts" in a longitudinal clinical study.

This paper attempts to identify characteristics of a longitudinal clinical study's "dropout" population (1974-1996) of patients using overdentures. This study included 395 subjects. Dropouts were identified as persons who did not respond to letters or telephone calls after participating in the study for up to 2 years, could not be located, or did not wish to return to the study. Participants (N=273) and Dropouts (N=84) were compared by evaluating a series of factors: sociodemographic, medical, health, and some oral health behaviors. The population was divided into two very similar cohorts for analysis based on years of recruitment: Group I (1974-1984) and Group II (1985-1993). Significant differences were found between them, including vision problems and risk of oral soft tissue problems related to medical diagnosis. Dropouts were significantly younger than Participants, had fewer hearing and vision problems, tended to brush their teeth more often and were more likely to use daily topical fluoride in their overdentures. The differences between the Dropouts and the Participants may be that younger persons are more mobile and have fewer vision and hearing problems, but this does not help predict their commitment to a study. Health behaviors such as brushing overdenture abutments or fluoride use may be more predictable but are harder to assess until persons have been study participants for some time.

Adolescent↗
PubMed2006

A package of interventions to reduce school dropout in public schools in a developing country. A feasibility study.

OBJECTIVE: School dropout rates are staggeringly high in developing countries, even for elementary school children. This study aims to assess the feasibility and initial efficacy of a package of interventions tailored to reduce school dropout in public schools in an urban city in Brazil. METHOD: Two public schools with similar high rates of dropout in elementary grades were selected. In one of them, a package of universal preventive interventions was implemented during a school year, including two workshops with teachers, five informative letters to parents, three meetings with parents at school, a telephone helpline at school, and a 1-day cognitive intervention. For children who stayed ten consecutive days out of school without reason, mental health assessment and referral to mental health services in the community were offered. In the second school, no intervention was implemented. RESULTS: After this 1-year intervention, there were significant differences between the two schools in rates of both dropout (P < 0.001) and absenteeism in the last trimester (P < 0.05; effect size = 0.64). In the intervention school, 18 (45%) youths returned to school after intervention among the 40 at-risk students. Moderate engagement of school staff was the main logistic problem. CONCLUSIONS: Our findings suggest that programs combining universal primary preventive strategies and interventions focused on at-risk students can be implemented and useful in developing countries to reduce school dropout.

Adolescent↗
PubMed1989

Adolescents' dropout from individual psychotherapy--is it true?

Although adolescent patients are said to have a propensity to drop out from psychotherapy, and clinical experiences seem to support this view, few studies have systematically examined this issue. However, a review of researches on adults' dropout shows that dropout is a serious problem for psychotherapy with adult patients. Moreover, available evidence on adolescents' dropout suggests that there is no significant difference in the rates of dropout from psychotherapy between adolescent patients and adult ones. In order to understand the specific quality of adolescents' dropout, the termination of psychotherapy with an adolescent patient is described and discussed. The view is put forward that it is because of the strong counter-transference feelings evoked in the therapist, when his adolescent patient leaves him prematurely, tends to maintain the impression of adolescents' proclivity to drop out from psychotherapy.

Acting Out↗
PubMed1994

The cost of treatment dropout in depression. A cost-benefit analysis of fluoxetine vs. tricyclics.

In this study, we tried to estimate the economic potential benefit of the use of fluoxetine (PROZACR 20 mg, Lilly) versus tricyclic antidepressants (TCAs) in depression of mild to moderate intensity. Fluoxetine has demonstrated, in controlled studies, significantly lower rates of side-effects and treatment dropout than TCAs while showing similar efficacy. Treatment dropout, especially at an early stage of the therapy, can have profound consequences, including excessive lengthening of the depressive episode, symptomatic relapse, increase of repeated days out of work, even suicides or suicide attempts. We estimated the expected cost of treatment dropout using a Delphi expert panel. We then computed the economic benefit of fluoxetine by combining the dropout cost and the differential rate of total treatment dropout between fluoxetine and TCAs, as found in clinical trials. We thus showed that a 8 week fluoxetine could be beneficial to society provided society values a year of human life above a threshold varying from French Francs 23.800 to FF8.600 (respectively, about US$4500 and 1600) depending on the type of depression. As these values are extremely low compared to those found in the literature, we concluded that an apparently costly innovation such as fluoxetine may induce short-term financial savings for society.

Antidepressive Agents, Tricyclic↗
PubMed2002

Prolonged exposure in patients with chronic PTSD: predictors of treatment outcome and dropout.

The present study investigated predictors of treatment outcome and dropout in two samples of PTSD-patients with mixed traumas treated using prolonged imaginal exposure. Possible predictors were analysed in both samples separately, in order to replicate in one sample findings found in the other. The only stable finding across the two groups was that patients who showed more PTSD-symptoms at pre-treatment, showed more PTSD-symptoms at post-treatment and follow-up. Indications were found that benzodiazepine use was related to both treatment outcome and dropout, and alcohol use to dropout. Demographic variables, depression and general anxiety, personality, trauma characteristics, feelings of anger, guilt, and shame and nonspecific variables regarding therapy were not related to either treatment outcome or dropout, disconfirming generally held beliefs about these factors as contra-indications for exposure therapy. It is concluded that it is difficult to use pre-treatment variables as a powerful and reliable tool for predicting treatment outcome or dropout. Clinically seen, it is therefore argued that exclusion of PTSD-patients from prolonged exposure treatment on the basis of pre-treatment characteristics is not justified.

Adolescent↗