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1.
Craig H. Mallinckrodt Christopher J. Kaiser John G. Watkin Michael J. Detke Geert Molenberghs Raymond J. Carroll 《Pharmaceutical statistics》2004,3(3):171-186
The last observation carried forward (LOCF) approach is commonly utilized to handle missing values in the primary analysis of clinical trials. However, recent evidence suggests that likelihood‐based analyses developed under the missing at random (MAR) framework are sensible alternatives. The objective of this study was to assess the Type I error rates from a likelihood‐based MAR approach – mixed‐model repeated measures (MMRM) – compared with LOCF when estimating treatment contrasts for mean change from baseline to endpoint (Δ). Data emulating neuropsychiatric clinical trials were simulated in a 4 × 4 factorial arrangement of scenarios, using four patterns of mean changes over time and four strategies for deleting data to generate subject dropout via an MAR mechanism. In data with no dropout, estimates of Δ and SEΔ from MMRM and LOCF were identical. In data with dropout, the Type I error rates (averaged across all scenarios) for MMRM and LOCF were 5.49% and 16.76%, respectively. In 11 of the 16 scenarios, the Type I error rate from MMRM was at least 1.00% closer to the expected rate of 5.00% than the corresponding rate from LOCF. In no scenario did LOCF yield a Type I error rate that was at least 1.00% closer to the expected rate than the corresponding rate from MMRM. The average estimate of SEΔ from MMRM was greater in data with dropout than in complete data, whereas the average estimate of SEΔ from LOCF was smaller in data with dropout than in complete data, suggesting that standard errors from MMRM better reflected the uncertainty in the data. The results from this investigation support those from previous studies, which found that MMRM provided reasonable control of Type I error even in the presence of MNAR missingness. No universally best approach to analysis of longitudinal data exists. However, likelihood‐based MAR approaches have been shown to perform well in a variety of situations and are a sensible alternative to the LOCF approach. MNAR methods can be used within a sensitivity analysis framework to test the potential presence and impact of MNAR data, thereby assessing robustness of results from an MAR method. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
Craig H. Mallinckrodt John G. Watkin Geert Molenberghs Raymond J. Carroll 《Pharmaceutical statistics》2004,3(3):161-169
Missing data, and the bias they can cause, are an almost ever‐present concern in clinical trials. The last observation carried forward (LOCF) approach has been frequently utilized to handle missing data in clinical trials, and is often specified in conjunction with analysis of variance (LOCF ANOVA) for the primary analysis. Considerable advances in statistical methodology, and in our ability to implement these methods, have been made in recent years. Likelihood‐based, mixed‐effects model approaches implemented under the missing at random (MAR) framework are now easy to implement, and are commonly used to analyse clinical trial data. Furthermore, such approaches are more robust to the biases from missing data, and provide better control of Type I and Type II errors than LOCF ANOVA. Empirical research and analytic proof have demonstrated that the behaviour of LOCF is uncertain, and in many situations it has not been conservative. Using LOCF as a composite measure of safety, tolerability and efficacy can lead to erroneous conclusions regarding the effectiveness of a drug. This approach also violates the fundamental basis of statistics as it involves testing an outcome that is not a physical parameter of the population, but rather a quantity that can be influenced by investigator behaviour, trial design, etc. Practice should shift away from using LOCF ANOVA as the primary analysis and focus on likelihood‐based, mixed‐effects model approaches developed under the MAR framework, with missing not at random methods used to assess robustness of the primary analysis. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
3.
4.
Archie B. Carroll 《Long Range Planning》1978,11(2):35-38
In this article the author argues that more formality in social responsibility planning efforts is a concept which is extremely pertinent in today's conditions. Rewards will accrue to the organization that can move beyond aesthetic objectives and achieve operationality in social responsibility goal setting. This requires, basically, the application of techniques that have proved to be successful in MBO programs. By translating broadly stated social objectives into goals that are clear, concise, time related and cost related, management will inject an increased measure of integrity into its planning process, improve social responsibility programs, assure future successes in the social performance arena, facilitate the appraisal of management personnel, and enhance the organization's credibility with its multiple publics. Positive benefits will flow to the organization, its immediate publics, and to the society at large as a consequence of operational planning methods as described herein. 相似文献
5.
Joshua N. Sampson Charles E. Matthews Laurence S. Freedman Raymond J. Carroll Victor Kipnis 《Journal of applied statistics》2016,43(9):1706-1721
Sedentary behavior has already been associated with mortality, cardiovascular disease, and cancer. Questionnaires are an affordable tool for measuring sedentary behavior in large epidemiological studies. Here, we introduce and evaluate two statistical methods for quantifying measurement error in questionnaires. Accurate estimates are needed for assessing questionnaire quality. The two methods would be applied to validation studies that measure a sedentary behavior by both questionnaire and accelerometer on multiple days. The first method fits a reduced model by assuming the accelerometer is without error, while the second method fits a more complete model that allows both measures to have error. Because accelerometers tend to be highly accurate, we show that ignoring the accelerometer's measurement error, can result in more accurate estimates of measurement error in some scenarios. In this article, we derive asymptotic approximations for the mean-squared error of the estimated parameters from both methods, evaluate their dependence on study design and behavior characteristics, and offer an R package so investigators can make an informed choice between the two methods. We demonstrate the difference between the two methods in a recent validation study comparing previous day recalls to an accelerometer-based ActivPal. 相似文献
6.
Germán A. Cadenas Nathalie Lynn Katherine Melo Li Lian Liu Elizabeth Angélica Cantú Alissa Ruth Sabrina Carroll Simeon Kulp Tameka Spence 《The Career development quarterly》2020,68(4):302-317
A need exists to better understand how racial/ethnic minority students' critical consciousness development in response to marginalization may be involved in their educational and career development. We therefore examined the link between critical consciousness development and career decision self-efficacy and career outcome expectations among racial/ethnic minority community college students. Following social cognitive career theory's conceptual pillars, we developed a testable model integrating critical consciousness and social cognitive variables. This model was tested with 135 racially and ethnically diverse community college students. Data analysis included path analyses and tests of model fit using structural equation modeling. Results suggested that (a) higher critical agency is linked to higher career decision self-efficacy and outcome expectations and (b) critical action and reflection have a bidirectional link and predict higher critical agency. Implications for research and practice aiming to close educational and career gaps among racial/ethnic minorities are discussed. 相似文献
7.
Carroll KJ 《Pharmaceutical statistics》2006,5(4):283-293
In oncology, it may not always be possible to evaluate the efficacy of new medicines in placebo-controlled trials. Furthermore, while some newer, biologically targeted anti-cancer treatments may be expected to deliver therapeutic benefit in terms of better tolerability or improved symptom control, they may not always be expected to provide increased efficacy relative to existing therapies. This naturally leads to the use of active-control, non-inferiority trials to evaluate such treatments. In recent evaluations of anti-cancer treatments, the non-inferiority margin has often been defined in terms of demonstrating that at least 50% of the active control effect has been retained by the new drug using methods such as those described by Rothmann et al., Statistics in Medicine 2003; 22:239-264 and Wang and Hung Controlled Clinical Trials 2003; 24:147-155. However, this approach can lead to prohibitively large clinical trials and results in a tendency to dichotomize trial outcome as either 'success' or 'failure' and thus oversimplifies interpretation. With relatively modest modification, these methods can be used to define a stepwise approach to design and analysis. In the first design step, the trial is sized to show indirectly that the new drug would have beaten placebo; in the second analysis step, the probability that the new drug is superior to placebo is assessed and, if sufficiently high in the third and final step, the relative efficacy of the new drug to control is assessed on a continuum of effect retention via an 'effect retention likelihood plot'. This stepwise approach is likely to provide a more complete assessment of relative efficacy so that the value of new treatments can be better judged. 相似文献
8.
While recent studies have suggested that the timing of sexual initiation within a couple's romantic relationship has important associations with later relationship success, few studies have examined how such timing is associated with relationship quality among unmarried couples. Using a sample of 10,932 individuals in unmarried, romantic relationships, we examined how four sexual-timing patterns (i.e., having sex prior to dating, initiating sex on the first date or shortly after, having sex after a few weeks of dating, and sexual abstinence) were associated with relationship satisfaction, stability, and communication in dating relationships. Results suggested that waiting to initiate sexual intimacy in unmarried relationships was generally associated with positive outcomes. This effect was strongly moderated by relationship length, with individuals who reported early sexual initiation reporting increasingly lower outcomes in relationships of longer than two years. 相似文献
9.
Devine CM Maley M Farrell TJ Warren B Sadigov S Carroll J 《Evaluation and program planning》2012,35(1):88-96
Small Steps are Easier Together (SS) was a pilot environmental intervention in small rural worksites in Upstate New York in collaboration with Extension educators. Worksite leaders teamed with co-workers to select and implement environmental changes to increase walking steps over individual baseline and to choose healthy eating options over 10 weeks. Participants were 226 primarily white, women employees in 5 sites. A mixed methods process evaluation, conducted to identify determinants of intervention effectiveness and to explain differences in outcomes across worksites, included surveys, self-reports of walking and eating, interviews, focus groups, and an intervention log. The evaluation assessed reach, characteristics of recruited participants, dose delivered, dose received, and context and compared sites on walking and eating outcomes. Emergent elements of participant-reported dose received included: active leadership, visible environmental changes, critical mass of participants, public display of accomplishments, accountability to co-workers, and group decision making. Participants at sites with high reach and dose were significantly more likely than sites with low reach and dose to achieve intervention goals. Although this small pilot needs replication, these findings describe how these evaluation methods can be applied and analyzed in an environmental intervention and provide information on trends in the data. 相似文献
10.
Carroll Haak Anika Rasner 《KZfSS K?lner Zeitschrift für Soziologie und Sozialpsychologie》2009,61(2):235-258
Previous research shows that college graduates in the humanities face a notably difficult college-to-work transition compared to graduates from other disciplines. Their transition to work not only takes longer; graduates in the humanities are also more likely to wind up in atypical employment. This paper asks, what factors explain the difficulties in the college-to-work transition for graduates in the humanities. Taking an interdisciplinary perspective, graduates in the humanities are compared to two reference groups: law and economics as well as engineering. Using data from the HIS Absolventenpanel 1997, separate piecewise constant hazard regression models were estimated to identify the determinants of the college-to-work transition for each discipline. Drawing on Spence’s theory of signaling and Rosenbaum’s tournament theory, we find that tournaments and signals structure the college-to-work transition differently in each discipline. While selection processes are weak in the humanities, graduates need to acquire additional occupationally useful skills before or during their studies in order to make a smoother transition into the labor market. 相似文献