BACKGROUND: Old people (75+) are underrepresented in studies on the prevalence of and risk factor... more BACKGROUND: Old people (75+) are underrepresented in studies on the prevalence of and risk factors for depression while the number of elderly people suffering from this mood disorder may be considerably higher than previously assumed. The role--if any--of age and gender in 'Geriatric Depression' is still unclear. METHODS: In this community-based study, prevalence of depressive symptomatology and risk indicators were assessed in 2850 participants aged 75 years or more. A clinically relevant level of depressive symptoms was defined as a score of > or =16 on the Centre for Epidemiologic Studies Depression scale (CES-D). Demographic data and questions related to physical and psychological health were recorded. Simple and multiple logistic regression techniques were used to determine the risk indicators (Odds Ratios, OR, with 95% confidence intervals, CI) with apparent importance to this population. RESULTS: The prevalence of depressive symptoms was assessed to be 31.1%. This ...
Many studies in the social and behavioral sciences involve multivariate discrete measurements, wh... more Many studies in the social and behavioral sciences involve multivariate discrete measurements, which are often characterized by the presence of an underlying individual trait, the existence of clusters such as domains of measurements, and the availability of multiple waves of cohort data. Motivated by an application in child development, we propose a class of extended multivariate discrete hidden Markov models for analyzing domain-based measurements of cognition and behavior. A random effects model is used to capture the long-term trait. Additionally, we develop a model selection criterion based on the Bayes factor for the extended hidden Markov model. The National Longitudinal Survey of Youth (NLSY) is used to illustrate the methods. Supplementary technical details and computer codes are available online.
The British journal of mathematical and statistical psychology, 2015
Many probabilistic models for psychological and educational measurements contain latent variables... more Many probabilistic models for psychological and educational measurements contain latent variables. Well-known examples are factor analysis, item response theory, and latent class model families. We discuss what is referred to as the 'explaining-away' phenomenon in the context of such latent variable models. This phenomenon can occur when multiple latent variables are related to the same observed variable, and can elicit seemingly counterintuitive conditional dependencies between latent variables given observed variables. We illustrate the implications of explaining away for a number of well-known latent variable models by using both theoretical and real data examples.
In order to identify persons who are at risk for dementia in an early phase, two classification t... more In order to identify persons who are at risk for dementia in an early phase, two classification trees were developed. Data were used from the Longitudinal Aging Study Amsterdam (LASA). The prevalence of dementia in the whole sample was 4.0%. In the first tree age seemed to be the strongest predictor, with an increased risk for persons older than 75. In this group the positive predictive value reached a maximum of 33.3% when the persons had memory complaints and a score on the Mini Mental State Examination (MMSE) <24. In a second classification tree, age was excluded as a predictor because of high association with the other potential predictors. In this tree functional limitations seemed the strongest predictor. In the group of persons with at least one functional limitations, the positive predictive value reached a maximum of 28.8% when the persons had memory complaints and a score <24 on the MMSE. In persons without memory complaints, persons with cardiovascular diseases or d...
Mixed models take the dependency between observations based on the same person into account by in... more Mixed models take the dependency between observations based on the same person into account by introducing one or more random effects. After introducing the mixed model framework, it is explained, by taking the Rasch model as a generic example, how item response models can be conceptualized as generalized linear and nonlinear mixed models. Common estimation methods for generalized linear and nonlinear models are discussed. In a simulation study, the performance of four estimation methods is assessed for the Rasch model under different conditions regarding the number of items and persons, and the degree of interindividual differences. The estimation methods included in the study are: an approximation of the integral over the random effect by means of Gaussian quadrature; direct maximization with a sixth-order Laplace approximation to the integrand; a linearized approximation of the nonlinear model employing PQL2; and finally a Bayesian MCMC method. It is concluded that the estimation...
Cellular oncology : the official journal of the International Society for Cellular Oncology, 2007
Mutational analysis of the Epidermal Growth Factor Receptor (EGFR) and K-ras genes to select non-... more Mutational analysis of the Epidermal Growth Factor Receptor (EGFR) and K-ras genes to select non-small cell lung cancer (NSCLC) patients for treatment with novel EGFR tyrosine kinase inhibitors is an appealing possibility currently under investigation. Although frozen tumor tissue would probably be the optimal source for analysis, the most common source of tumor material is fixed and paraffin embedded (FPE) archival specimens. Here, we evaluate how different procedures of tissue sample processing and preservation may affect the outcome of EGFR and K-ras mutation analysis. Furthermore, we compare the sensitivity of the analysis using genomic DNA (gDNA) versus RNA. We used PCR amplification and direct sequencing to analyze EGFR and K-ras genes in paired FPE and frozen tumor samples corresponding to 47 NSCLC patients. In frozen samples, the analysis was carried out using both gDNA and RNA extracted in parallel. Whereas 100% of frozen samples were successfully amplified, the rate of suc...
ABSTRACT Second-order item response theory models have been used for assessments consisting of se... more ABSTRACT Second-order item response theory models have been used for assessments consisting of several domains, such as content areas. We extend the second-order model to a third-order model for assessments that include subdomains nested in domains. Using a graphical model framework, it is shown how the model does not suffer from the curse of multidimensionality. We apply unidimensional, second-order, and third-order item response models to the 2007 Trends in International Mathematics and Science Study. Our findings suggest that deviations from unidimensionality are more pronounced at the content domain level than at the cognitive domain level and that deviations from unidimensionality at the content domain level become negligible after taking into account topic areas.
Studies indicated that 5-aminosalicylates (5-ASA) may influence the metabolism of thiopurines; ho... more Studies indicated that 5-aminosalicylates (5-ASA) may influence the metabolism of thiopurines; however, conclusions were restricted as a result of number of patients or study design. To determine the influence of 5-ASA on thiopurine metabolism, we performed a prospective multicenter pharmacokinetic interaction study of two different 5-ASA dosages (2 g daily followed by 4 g daily) in 26 inflammatory bowel disease (IBD) patients during steady-state AZA or 6-MP therapy. The 4-wk coadministration of 2 g 5-ASA daily, followed by a 4-wk period of 4 g 5-ASA daily, led to a statistical significant increase of 40% (absolute 84 pmol/8x10(8) RBC) and 70% (absolute 154 pmol/8x10(8) RBC) in 6-thioguaninenucleotide levels (6-TGN), respectively. A rise in 6-TGN levels was observed in 100% of patients after a 4-wk period of 4 g 5-ASA daily. The 6-methylmercaptopurine-ribonucleotide levels did not change. Signs of myelotoxicity were observed in 7.7% of patients (N=2). The level of the pharmacologically active 6-TGN significantly increases in a dose-dependent manner during 5-ASA coadministration. IBD patients who are unresponsive or refractory to standard thiopurine therapy may benefit from the coadministration of 5-ASA, leading to an increase in 6-TGN levels.
BACKGROUND: Old people (75+) are underrepresented in studies on the prevalence of and risk factor... more BACKGROUND: Old people (75+) are underrepresented in studies on the prevalence of and risk factors for depression while the number of elderly people suffering from this mood disorder may be considerably higher than previously assumed. The role--if any--of age and gender in 'Geriatric Depression' is still unclear. METHODS: In this community-based study, prevalence of depressive symptomatology and risk indicators were assessed in 2850 participants aged 75 years or more. A clinically relevant level of depressive symptoms was defined as a score of > or =16 on the Centre for Epidemiologic Studies Depression scale (CES-D). Demographic data and questions related to physical and psychological health were recorded. Simple and multiple logistic regression techniques were used to determine the risk indicators (Odds Ratios, OR, with 95% confidence intervals, CI) with apparent importance to this population. RESULTS: The prevalence of depressive symptoms was assessed to be 31.1%. This ...
Many studies in the social and behavioral sciences involve multivariate discrete measurements, wh... more Many studies in the social and behavioral sciences involve multivariate discrete measurements, which are often characterized by the presence of an underlying individual trait, the existence of clusters such as domains of measurements, and the availability of multiple waves of cohort data. Motivated by an application in child development, we propose a class of extended multivariate discrete hidden Markov models for analyzing domain-based measurements of cognition and behavior. A random effects model is used to capture the long-term trait. Additionally, we develop a model selection criterion based on the Bayes factor for the extended hidden Markov model. The National Longitudinal Survey of Youth (NLSY) is used to illustrate the methods. Supplementary technical details and computer codes are available online.
The British journal of mathematical and statistical psychology, 2015
Many probabilistic models for psychological and educational measurements contain latent variables... more Many probabilistic models for psychological and educational measurements contain latent variables. Well-known examples are factor analysis, item response theory, and latent class model families. We discuss what is referred to as the 'explaining-away' phenomenon in the context of such latent variable models. This phenomenon can occur when multiple latent variables are related to the same observed variable, and can elicit seemingly counterintuitive conditional dependencies between latent variables given observed variables. We illustrate the implications of explaining away for a number of well-known latent variable models by using both theoretical and real data examples.
In order to identify persons who are at risk for dementia in an early phase, two classification t... more In order to identify persons who are at risk for dementia in an early phase, two classification trees were developed. Data were used from the Longitudinal Aging Study Amsterdam (LASA). The prevalence of dementia in the whole sample was 4.0%. In the first tree age seemed to be the strongest predictor, with an increased risk for persons older than 75. In this group the positive predictive value reached a maximum of 33.3% when the persons had memory complaints and a score on the Mini Mental State Examination (MMSE) <24. In a second classification tree, age was excluded as a predictor because of high association with the other potential predictors. In this tree functional limitations seemed the strongest predictor. In the group of persons with at least one functional limitations, the positive predictive value reached a maximum of 28.8% when the persons had memory complaints and a score <24 on the MMSE. In persons without memory complaints, persons with cardiovascular diseases or d...
Mixed models take the dependency between observations based on the same person into account by in... more Mixed models take the dependency between observations based on the same person into account by introducing one or more random effects. After introducing the mixed model framework, it is explained, by taking the Rasch model as a generic example, how item response models can be conceptualized as generalized linear and nonlinear mixed models. Common estimation methods for generalized linear and nonlinear models are discussed. In a simulation study, the performance of four estimation methods is assessed for the Rasch model under different conditions regarding the number of items and persons, and the degree of interindividual differences. The estimation methods included in the study are: an approximation of the integral over the random effect by means of Gaussian quadrature; direct maximization with a sixth-order Laplace approximation to the integrand; a linearized approximation of the nonlinear model employing PQL2; and finally a Bayesian MCMC method. It is concluded that the estimation...
Cellular oncology : the official journal of the International Society for Cellular Oncology, 2007
Mutational analysis of the Epidermal Growth Factor Receptor (EGFR) and K-ras genes to select non-... more Mutational analysis of the Epidermal Growth Factor Receptor (EGFR) and K-ras genes to select non-small cell lung cancer (NSCLC) patients for treatment with novel EGFR tyrosine kinase inhibitors is an appealing possibility currently under investigation. Although frozen tumor tissue would probably be the optimal source for analysis, the most common source of tumor material is fixed and paraffin embedded (FPE) archival specimens. Here, we evaluate how different procedures of tissue sample processing and preservation may affect the outcome of EGFR and K-ras mutation analysis. Furthermore, we compare the sensitivity of the analysis using genomic DNA (gDNA) versus RNA. We used PCR amplification and direct sequencing to analyze EGFR and K-ras genes in paired FPE and frozen tumor samples corresponding to 47 NSCLC patients. In frozen samples, the analysis was carried out using both gDNA and RNA extracted in parallel. Whereas 100% of frozen samples were successfully amplified, the rate of suc...
ABSTRACT Second-order item response theory models have been used for assessments consisting of se... more ABSTRACT Second-order item response theory models have been used for assessments consisting of several domains, such as content areas. We extend the second-order model to a third-order model for assessments that include subdomains nested in domains. Using a graphical model framework, it is shown how the model does not suffer from the curse of multidimensionality. We apply unidimensional, second-order, and third-order item response models to the 2007 Trends in International Mathematics and Science Study. Our findings suggest that deviations from unidimensionality are more pronounced at the content domain level than at the cognitive domain level and that deviations from unidimensionality at the content domain level become negligible after taking into account topic areas.
Studies indicated that 5-aminosalicylates (5-ASA) may influence the metabolism of thiopurines; ho... more Studies indicated that 5-aminosalicylates (5-ASA) may influence the metabolism of thiopurines; however, conclusions were restricted as a result of number of patients or study design. To determine the influence of 5-ASA on thiopurine metabolism, we performed a prospective multicenter pharmacokinetic interaction study of two different 5-ASA dosages (2 g daily followed by 4 g daily) in 26 inflammatory bowel disease (IBD) patients during steady-state AZA or 6-MP therapy. The 4-wk coadministration of 2 g 5-ASA daily, followed by a 4-wk period of 4 g 5-ASA daily, led to a statistical significant increase of 40% (absolute 84 pmol/8x10(8) RBC) and 70% (absolute 154 pmol/8x10(8) RBC) in 6-thioguaninenucleotide levels (6-TGN), respectively. A rise in 6-TGN levels was observed in 100% of patients after a 4-wk period of 4 g 5-ASA daily. The 6-methylmercaptopurine-ribonucleotide levels did not change. Signs of myelotoxicity were observed in 7.7% of patients (N=2). The level of the pharmacologically active 6-TGN significantly increases in a dose-dependent manner during 5-ASA coadministration. IBD patients who are unresponsive or refractory to standard thiopurine therapy may benefit from the coadministration of 5-ASA, leading to an increase in 6-TGN levels.
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Papers by Frank Rijmen