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Analysis of duration data from longitudinal surveys subject to loss to follow-upMariaca Hajducek, C. Dagmar January 2010 (has links)
Data from longitudinal surveys give rise to many statistical challenges. They often come from a vast, heterogeneous population and from a complex sampling design. Further, they are usually collected retrospectively at intermittent interviews spaced over a long period of time, which gives rise to missing information and loss to follow-up. As a result, duration data from this kind of surveys are subject to dependent censoring, which needs to be taken into account to prevent biased analysis. Methods for point and variance estimation are developed using Inverse Probability of Censoring (IPC) weights. These methods account for the random nature of the IPC weights and can be applied in the analysis of duration data in survey and non-survey settings. The IPC estimation techniques are based on parametric estimating function theory and involve the estimation of dropout models. Survival distributions without covariates are estimated via a weighted Kaplan-Meier method and regression modeling through the Cox Proportional Hazards model and other models is based on weighted estimating functions. The observational frameworks from Statistics Canada's Survey of Labour and Income Dynamics (SLID) and the UK Millenium Cohort Study are used as motivation, and durations of jobless spells from SLID are analyzed as an illustration of the methodology. Issues regarding missing information from longitudinal surveys are also discussed.
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Analysis of duration data from longitudinal surveys subject to loss to follow-upMariaca Hajducek, C. Dagmar January 2010 (has links)
Data from longitudinal surveys give rise to many statistical challenges. They often come from a vast, heterogeneous population and from a complex sampling design. Further, they are usually collected retrospectively at intermittent interviews spaced over a long period of time, which gives rise to missing information and loss to follow-up. As a result, duration data from this kind of surveys are subject to dependent censoring, which needs to be taken into account to prevent biased analysis. Methods for point and variance estimation are developed using Inverse Probability of Censoring (IPC) weights. These methods account for the random nature of the IPC weights and can be applied in the analysis of duration data in survey and non-survey settings. The IPC estimation techniques are based on parametric estimating function theory and involve the estimation of dropout models. Survival distributions without covariates are estimated via a weighted Kaplan-Meier method and regression modeling through the Cox Proportional Hazards model and other models is based on weighted estimating functions. The observational frameworks from Statistics Canada's Survey of Labour and Income Dynamics (SLID) and the UK Millenium Cohort Study are used as motivation, and durations of jobless spells from SLID are analyzed as an illustration of the methodology. Issues regarding missing information from longitudinal surveys are also discussed.
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Comparison of loss to follow-up amongst HIV and AIDS patients in care and treatment in Kisumu, KenyaMiruka, Fredrick Omondi January 2012 (has links)
Magister Public Health - MPH / Background: Even though there have been marked increases in the number of patients accessing HIV care and treatment in sub-Saharan Africa, challenges in patient retention remain. Most health systems in sub-Saharan Africa routinely report on loss to follow up of patients, but only a limited number of factors associated with loss to follow up are measured. In Kenya there is limited research on loss to follow up in HIV care and treatment programs. This study reports on rates of loss to follow up and factors associated with loss to follow up at the New NyanzaProvincial General Hospital (NNPGH) in Kisumu, Kenya. Methods: A retrospective cohort study of 4,740 adult patients that was registered for HIV and AIDS care and treatment between 2003 and 2008 was conducted. Data was analysed using SAS 9.2 and STATA 10. Cox proportional hazard ratio was calculated to describe the association between risk factors and loss to follow up. Results of the total 4740 patients, 64.6% were female, males [median age of 36 (IQR 30-44) years vs. 32 (IQR 26-39) years for females] were older than females, more males (68.3%) were married, more females (6.2%) had no education and 68% of all patients enrolled had been lost to follow up over 6 years. Risk for lost to follow up was greater amongst males (Adjusted Hazard Ratio (AHR) =1.12; 95% Confidence Interval (CI) = 1.02-1.22); younger patients(15-30 vs. >40 years: AHR=1.37, 95%CI = 1.23 – 1.53; and 31-40 vs. >40 years: AHR=1.15, 95%CI=1.03-1.28); those who were unemployed (AHR=1.14, 95%CI=1.05-1.25); and having advanced HIV disease (WHO stage 4 vs. WHO stage 1: AHR=1.53, 95%CI=1.29-1.81). Patients on ART (AHR=0.64, 95%CI=0.52-0.78) at enrollment were less likely to be lost to follow-up compared to those in HIV care. Conclusion: More attention is needed in developing retention strategies for patients with much focus on patients on care. Targeted intervention is required to improve retention amongst males, unemployed patients, patients with advanced HIV disease and younger patients. Additionally, targeted follow up in the community for patients on care is required.
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Characteristics of adult patients who are lost to follow-up in antiretroviral roll out clinics – Gauteng, South AfricaMolefe, Thuthukile 11 1900 (has links)
The global commitment by governments throughout the world to scaling up access to Antiretroviral Therapy (ART) in response to the crisis imposed by the HIV epidemic has resulted in a large number of people living with Human Immune-deficiency Virus (HIV) worldwide. According to statistics provided by the World Health Organization (WHO), there were approximately 35 million people living with HIV (PLWHIV) in 2012.1This large number of PLWHIV observed in recent years reflects the life-prolonging benefit effects of ART. / Dissertation (MSc)--University of Pretoria, 2014. / School of Health Systems and Public Health (SHSPH) / MSc / Unrestricted
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The Intention-to-Treat (ITI) Project: A Systematic Review of the Methodological LiteratureAlshurafa , Mohamad 10 1900 (has links)
<p>OBJECTIVES: The primary objective of this systematic review was to illustrate the various definitions authors of methodology articles have offered for intention to treat (ITT) in relation to loss to follow up (LTFU).</p> <p> METHODS: We searched MEDLINE® for publications appearing between 1950 to 2008. Eligible papers devoted at least one paragraph to ITT and two other paragraphs to either ITT or LTFU. Investigators independently extracted relevant information from each eligible article. Discrepancies between data extractors were adjudicated. Data was extracted and variables used during data extraction were analyzed using the Landis and Koch guidelines kappa values.</p> <p> RESULTS: The MEDLINE® search yielded 1007 articles. One-hundred and ten articles underwent full text screening yielding 66 articles. All kappa's were substantial to near perfect agreement (>0.74). Of the 66 articles, five (8%) did not define ITT, 25 (41%) mentioned LTFU but did not discuss its relationship with ITT, 36 (59%) commented on LTFU in the context of ITT. These 36 articles segregated into three distinctive definitions for ITT: "full-follow-up required" (mentioned 58%), "ITT and LTFU are separate issues" (mentioned 17%), and "ITI involves specific strategy for LTFU" (mentioned 78%). Of the 36 articles, 17 (47%) had multiple definitions for ITT. The most frequent strategies mentioned for handling LTFU were last outcome carried forward (50%), sensitivity analysis (50%), and use of available data to impute (46%). Most articles (81%) specifically excluded complete case analysis under ITI.</p> <p> CONCLUSION : The most striking finding of our systematic review is that there is
no meaningful consensus on the definition of ITI. This review, considered alongside previous reviews of RCTs, demonstrates that simply stating a study employed ITT is useless at best and misleading and dangerous at worst. It is the recommendation of this thesis that trialists replace the term ITI with a clear statements about analytic strategies applied to participants who were followed and with those not followed.</p> / Thesis / Master of Science (MS)
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Loss to follow-up among participants in the real talk study: a brief motivational interview intervention to reduce teen dating violence perpetration in BostonVelasquez, Gabriela Elizabeth 20 June 2016 (has links)
Loss to follow-up (LTF) is an important issue that can affect the validity of longitudinal studies. Further, LTF among adolescent study participants may be predicted by variables such as substance use, educational attainment, and demographic information. The purpose of this study was to determine if alcohol or marijuana use, high school completion, or demographic information was correlated with LTF among adolescent participants in the Real Talk Study. The Real Talk study is a randomized control trial that employs a brief motivational interview intervention in a clinical setting to reduce perpetration of teen dating violence (TDV) in Boston. Current participants of the Real Talk study who were eligible for follow up comprised the study sample (N=127). Baseline characteristics on age, gender, race/ethnicity, high school completion, alcohol use, and marijuana use were analyzed using Pearson’s Chi Square, and the level of significance set to p < 0.10. A post-hoc analysis was conducted on frequency of alcohol use using Pearson’s Chi Square. Of the total sample, 13% were LTF (n=17). The results of the analyses indicated that there was a statistically significant difference between those LTF and those retained for gender and drinking 6 or more drinks of alcohol per occasion. Females were more likely to be LTF than males (p<0.10), and those participants who responded “never” or “less than monthly” to the question, “how many times do you drink 6 or more drinks per occasion?” were more likely to be retained, or less likely to be LTF (p<0.10) than those who responded differently. While some of the results were consistent with the literature, it is also possible that the follow-up procedure for Real Talk ensured that there were minimal differences in LTF.
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Comparing the Statistical Power of Analysis of Covariance after Multiple Imputation and the Mixed Model in Testing the Treatment Effect for Pre-post Studies with Loss to Follow-upXi, Wenna 23 December 2014 (has links)
No description available.
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Avaliação do efeito das perdas de seguimento nas análises feitas pelo estimador produto - limite de Kaplan - Meier e pelo modelo de riscos proporcionais de Cox / The impact of the loss to follow-up when using the Kaplan Meier estimator and the Cox proportional hazard modelHolcman, Marcia Moreira 20 April 2006 (has links)
Introdução: As técnicas mais comumente empregadas em análise de sobrevida que utilizam dados censurados são o estimador produto limite de Kaplan-Meier (KM) e o modelo de riscos proporcionais de Cox. Estas técnicas têm como suposição que a causa da perda de seguimento seja independente do tempo de sobrevida. Objetivo: O presente estudo visa a analisar o efeito das perdas de seguimento nestas duas técnicas. Material e Métodos: O estudo foi realizado utilizando-se o banco de dados dos pacientes cadastrados no Registro Hospitalar do Hospital do Câncer de São Paulo em 1994. Foram elaborados 28 bancos de dados simulando perdas informativas e não informativas. A perda informativa foi simulada transformando os óbitos em vivos, na proporção de 5 a 50%. A perda não informativa foi simulada através do sorteio de 5 a 50% do total do banco. O estimador de Kaplan-Meier (KM) foi utilizado para estimar a sobrevida acumulada no primeiro, terceiro e quinto ano de seguimento, e o modelo de riscos proporcionais de Cox para estimar as hazard ratio (HR). Todas as estimativas obtidas no KM e as HR's foram comparadas com os resultados do banco de dados original. Resultados: Houve maior proporção de perda nos pacientes com maior escolaridade, admitidos por convênio e particular e os menos graves (estádio I ou II). Quanto maior a proporção de perda informativa, maior a diferença alcançada nas estimativas realizadas pelo KM, verificando-se que a perda de seguimento superior a 15% acarretou diferenças superiores a 20% nas estimativas da probabilidade de sobrevida. As HR's foram menos afetadas, e proporções superiores a 20% de perda de seguimento acarretaram variações de cerca de 10% nas estimativas. Quando as perdas foram não informativas não houve diferenças significativas nas estimativas pelo KM e nas HR's em relação ao banco original. Conclusões: É importante avaliar se as perdas ocorridas em estudos de coorte são informativas ou não, pois se forem podem acarretar distorções principalmente nas estimativas feitas pelo método de KM. / Introduction: The Kaplan Meier product limit estimator (KM) and the Cox proportional hazard (HR) model are the most used tools in survival analysis. These two methods have the key assumption that censoring must be independent from the survival time. Objective: To analyze the consequences of loss to follow up in these two methods. Methods: The study has utilized the data of the Cancer Registry of the patients of Hospital do Cancer in São Paulo of 1994. The informative censure was simulated transforming the death by 5 to 50% into alive. Besides 5 to 50% was spared at random simulating the non-informative censoring. The survival probability and was calculated to the first, third and fifth year of follow up. All the estimated probabilities and HRs were compared with the results of the original data. Results: Patients with greater scholars, lower stages and admitted by health plans or private had more losses to follow up. The maximum proportion of accepted loss to follow up is 10% to 15% when using the KM estimator, and the HR are less affected by the loss to follow-up and one can afford having 20% of it. When the losses were non informative there were no differences between the original probabilities. Conclusions: The possibility of over or under estimated probability must be analyzed in the presence of the losses to follow- up when using the KM and HR in survival analyses.
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Adherence, retention in care and treatment outcomes of adolescents on antiretroviral therapy in the Western Cape Metropole in South AfricaKriel, Ebrahim January 2017 (has links)
Magister Public Health - MPH (Public Health) / Approximately 6% of all people living with HIV in 2016 are adolescents aged
10-19 years. It is reported globally that adolescents on antiretroviral therapy (ART) are at
increased risk for poor retention in care, adherence and viral load suppression, compared to
children and adults.
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Avaliação do efeito das perdas de seguimento nas análises feitas pelo estimador produto - limite de Kaplan - Meier e pelo modelo de riscos proporcionais de Cox / The impact of the loss to follow-up when using the Kaplan Meier estimator and the Cox proportional hazard modelMarcia Moreira Holcman 20 April 2006 (has links)
Introdução: As técnicas mais comumente empregadas em análise de sobrevida que utilizam dados censurados são o estimador produto limite de Kaplan-Meier (KM) e o modelo de riscos proporcionais de Cox. Estas técnicas têm como suposição que a causa da perda de seguimento seja independente do tempo de sobrevida. Objetivo: O presente estudo visa a analisar o efeito das perdas de seguimento nestas duas técnicas. Material e Métodos: O estudo foi realizado utilizando-se o banco de dados dos pacientes cadastrados no Registro Hospitalar do Hospital do Câncer de São Paulo em 1994. Foram elaborados 28 bancos de dados simulando perdas informativas e não informativas. A perda informativa foi simulada transformando os óbitos em vivos, na proporção de 5 a 50%. A perda não informativa foi simulada através do sorteio de 5 a 50% do total do banco. O estimador de Kaplan-Meier (KM) foi utilizado para estimar a sobrevida acumulada no primeiro, terceiro e quinto ano de seguimento, e o modelo de riscos proporcionais de Cox para estimar as hazard ratio (HR). Todas as estimativas obtidas no KM e as HR's foram comparadas com os resultados do banco de dados original. Resultados: Houve maior proporção de perda nos pacientes com maior escolaridade, admitidos por convênio e particular e os menos graves (estádio I ou II). Quanto maior a proporção de perda informativa, maior a diferença alcançada nas estimativas realizadas pelo KM, verificando-se que a perda de seguimento superior a 15% acarretou diferenças superiores a 20% nas estimativas da probabilidade de sobrevida. As HR's foram menos afetadas, e proporções superiores a 20% de perda de seguimento acarretaram variações de cerca de 10% nas estimativas. Quando as perdas foram não informativas não houve diferenças significativas nas estimativas pelo KM e nas HR's em relação ao banco original. Conclusões: É importante avaliar se as perdas ocorridas em estudos de coorte são informativas ou não, pois se forem podem acarretar distorções principalmente nas estimativas feitas pelo método de KM. / Introduction: The Kaplan Meier product limit estimator (KM) and the Cox proportional hazard (HR) model are the most used tools in survival analysis. These two methods have the key assumption that censoring must be independent from the survival time. Objective: To analyze the consequences of loss to follow up in these two methods. Methods: The study has utilized the data of the Cancer Registry of the patients of Hospital do Cancer in São Paulo of 1994. The informative censure was simulated transforming the death by 5 to 50% into alive. Besides 5 to 50% was spared at random simulating the non-informative censoring. The survival probability and was calculated to the first, third and fifth year of follow up. All the estimated probabilities and HRs were compared with the results of the original data. Results: Patients with greater scholars, lower stages and admitted by health plans or private had more losses to follow up. The maximum proportion of accepted loss to follow up is 10% to 15% when using the KM estimator, and the HR are less affected by the loss to follow-up and one can afford having 20% of it. When the losses were non informative there were no differences between the original probabilities. Conclusions: The possibility of over or under estimated probability must be analyzed in the presence of the losses to follow- up when using the KM and HR in survival analyses.
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