Papers by Guillermo Vallejo
Psicothema, 2006
The aim of the study was to provide a standardization of self-reported competences and emotional/... more The aim of the study was to provide a standardization of self-reported competences and emotional/behavioural problems in Spanish adolescents, using the Achenbach's Youth Self-Report (YSR), and to compare our results to those from other countries. The YSR was completed by 2822 adolescents aged 11-18 years, recruited from secondary schools in two regions of Spain. There were significant differences in Total behaviour problems and in most problem scales in boys and girls, scoring boys higher on externalizing syndromes, whereas girls score higher on internalizing syndromes . Males' mean scores were higher than females' scores for social competence. Age effects also showed significant differences with respect to internalizing problems, thought problems, social problems and depression. Cut-off points based on the 90th and 98th percentile developed from this sample are presented for the competences and the problem scales. To test the overall range of variations across cultures,...
Computer Methods and Programs in Biomedicine, 2006
Group-randomized study designs are useful when individually-randomized designs either are not pos... more Group-randomized study designs are useful when individually-randomized designs either are not possible, or will not be able to estimate the parameters of interest. Group-randomized trials often have small number of experimental units or groups and strong geographicallyinduced between-unit correlation, thereby increasing the chance of obtaining a "bad" randomization outcome. It has been suggested to highly constrain the design through restriction to those allocations that meet specified criteria based on certain covariates available at the baseline. We describe a SAS ® macro that allocates treatment conditions in a twoarm stratified group-randomized design that ensures balance on relevant covariates. The application of the macro is illustrated using two examples of group-randomized designs.
Behavior research methods, Jan 22, 2018
In this study, two approaches were employed to calculate how large the sample size needs to be in... more In this study, two approaches were employed to calculate how large the sample size needs to be in order to achieve a desired statistical power to detect a significant group-by-time interaction in longitudinal intervention studies-a power analysis method, based on derived formulas using ordinary least squares estimates, and an empirical method, based on restricted maximum likelihood estimates. The performance of both procedures was examined under four different scenarios: (a) complete data with homogeneous variances, (b) incomplete data with homogeneous variances, (c) complete data with heterogeneous variances, and (d) incomplete data with heterogeneous variances. Several interesting findings emerged from this research. First, in the presence of heterogeneity, larger sample sizes are required in order to attain a desired nominal power. The second interesting finding is that, when there is attrition, the sample size requirements can be quite large. However, when attrition is anticipat...
Amenazas a la validez analítica de las técnicas usadas habitualmente en la evaluación de programas
Revista latinoamericana de psicología
The purpose of this investigation was assessing the robustness of a series of new procedures unde... more The purpose of this investigation was assessing the robustness of a series of new procedures under the traditional ANOVA approach to analyze some data corresponding to repeated measures by means of Monte Carlo simulation. In order to study the efficacy of these procedures for the control of Type I rate of errors, four variables were handled: sample size; structure of dispersion matrixes; relationship between the group sizes and the dispersion matrices, and population distribution pattern. Results suggest that the Improved General Approach, Proc Mixed program with the Kenward-Roger solution, Brown-Forsythe and Welch James procedures offer a very good behavior to control the Type I rate of errors both for the main effect of the measurement opportunities as well as the effect of interaction, under all the assessed conditions.
FERNÁNDEZ et al. Prueba estadística para un diseño de medidas repetidas Int ABSTRACT. The power a... more FERNÁNDEZ et al. Prueba estadística para un diseño de medidas repetidas Int ABSTRACT. The power and robustness of the statistical procedures for the analysis of the repeated measures designs' effects are sensitive to the not satisfaction of the analysis assumptions, especially, the assumption of sphericity and homogeneity of the covariance matrices. Unfortunately, the violation of these assumptions is habitual in the data of the educational and psychological applied research. In this theoretical study we examined the performance of the several statistics procedures with regard to the Type I error and the power obtained for several authors through Monte Carlo methods. As well a Monte Carlo investigation was conduced ad hoc for exemplify the quantity of the Type I error in the within-subject effects in a split-plot repeated measures design. Examinee all previous we advise that different methods of analysis are appropriate in different situations and we conclude bringing recommendations for the analysis of these designs in order of the violation or not of the derivational assumptions. KEYWORDS. Repeated measures. Applied research. Statistical procedures. Violation of assumptions. Recommendations. Theoretical study.
Modelo lineal general mixto: Alternativa a los modelos de análisis clásicos
Personality and Individual Differences, 2016
Self-esteem is one of the variables that are most frequently linked to the adoption of self-prote... more Self-esteem is one of the variables that are most frequently linked to the adoption of self-protection strategies. However, the nature of this relationship continues to be controversial. The present study examines the relationship between self-esteem and the use of behavioral and claimed self-handicapping, as well as of defensive pessimism, and their relationship with gender in university students. A total of 1031 university students took part in the study. For women, polynomial regression analysis demonstrated a negative linear relationship of claimed self-handicapping and a tendency toward a quadratic relationship in the case of behavioral self-handicapping, as well as a mainly quadratic relationship in the use of defensive pessimism. For men, a negative linear relationship was found in all cases. The theoretical and psychoeducational implications of these findings are discussed.
Impacto de los instrumentos evaluativos en el nuevo modelo de formación en la asignatura Morfofisiología
E Agradecimientos La Fundación CEAM está financiada por la Generalitat Valenciana y Bancaixa.
Values in nursing students and professionals: An exploratory comparative study
Nursing Ethics
Many studies have explored personal values in nursing, but none has assessed whether the predicti... more Many studies have explored personal values in nursing, but none has assessed whether the predictions made by the theory of intergenerational value change are true for the different generations of nursing professionals and students. This theory predicts a shift in those personal values held by younger generations towards ones focussed on self-expression. The purpose of the study was to identify intergenerational differences in personal values among nursing professionals and nursing students and to determine whether generational value profiles fit the predictions made by the theory. An exploratory comparative design with a cross-sectional survey method was used. Participants were recruited from four public hospitals and 10 Primary Care Centres in medium-size cities in Spain. A sample of 589 nurses and 2295 nursing students participated in the study. An open survey method was used to collect data that were classified grouping reported values into categories following a method of value ...
Transplantation proceedings, 2003
Our aim was to validate Spanish and Catalan versions of the Liver Disease Quality of Life questio... more Our aim was to validate Spanish and Catalan versions of the Liver Disease Quality of Life questionnaire (LDQOL) for use in liver transplant patients. The LDQOL consists of the SF-36 generic measure of health-related quality of life (HRQOL) and 12 disease-specific dimensions for liver disease patients. The Spanish and Catalan versions of the questionnaire were administered to 138 patients with a liver transplant. Cronbach's alpha coefficients (CAC) were used to test the internal consistency of disease-specific scales. Test-retest reliability was calculated using the Intraclass Correlation Coefficient (ICC) in a sub-group of 41 patients who completed the questionnaire on two occasions 1 to 2 weeks apart. Validity was analysed by determining the instrument's capacity to discriminate between patient groups classified according to years since transplant, disease etiology, and symptom severity. Ceiling and floor effects were also calculated. Internal consistency in the disease-spe...
The Pharmacogenomics Journal, 2007
N-acetyltransferase 2 (NAT2), an important enzyme in clinical pharmacology, metabolizes antibioti... more N-acetyltransferase 2 (NAT2), an important enzyme in clinical pharmacology, metabolizes antibiotics such as isoniazid and sulfamethoxazole, and catalyzes the transformation of aromatic and heterocyclic amines from the environment and diet into carcinogenic intermediates. Polymorphisms in NAT2 account for variability in the acetylator phenotype and the pharmacokinetics of metabolized drugs. Native Americans, settled in rural areas and large cities of Latin America, are under-represented in pharmacogenetics studies; therefore, we sequenced the coding region of NAT2 in 456 chromosomes from 13 populations from the Americas, and two from Siberia, detecting nine substitutions and 11 haplotypes. Variants *4 (37%), *5B (23%) and *7B (24%) showed high frequencies. Average frequencies of fast, intermediate and slow acetylators across Native Americans were 18, 56 and 25%, respectively. NAT2 intra-population genetic diversity for Native Americans is higher than East Asians and similar to the rest of the world, and NAT2 variants are homogeneously distributed across native populations of the continent.
Effects of Covariance Heterogeneity on Three Procedures for Analyzing Multivariate Repeated Measures Designs
Multivariate Behavioral Research, 2001
Empirical Type I error and power rates were estimated for (a) the doubly multivariate model,(b) t... more Empirical Type I error and power rates were estimated for (a) the doubly multivariate model,(b) the Welch-James multivariate solution developed by Keselman, Carriere and Lix (1993) using Johansen's results (1980), and for (c) the multivariate version of the modified ...
Human Mutation, 2005
A collaborative work was carried out by the Spanish and Portuguese ISFG Working Group (GEP-ISFG) ... more A collaborative work was carried out by the Spanish and Portuguese ISFG Working Group (GEP-ISFG) to estimate Y-STR mutation rates. Seventeen Y chromosome STR loci (DYS19, DYS385, DYS389I and II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS460, DYS461, DYS635 [GATA C4], GATA H4, and GATA A10) were analyzed in a sample of 3,026 father/son pairs. Among 27,029 allele transfers, 54 mutations were observed, with an overall mutation rate across the 17 loci of 1.998 Â 10 -3 (95% CI, 1.501 Â 10 -3 to 2.606 Â 10 -3 ). With just one exception, all of the mutations were single-step, and they were observed only once per gametogenesis. Repeat gains were more frequent than losses, longer alleles were found to be more mutable, and the mutation rate seemed to increase with the father's age. Hum Mutat 26 , 520-528, 2005. r r 2005 Wiley-Liss, Inc. Grant sponsor: Fundac -a ì o para a Cie OE ncia e a Tecnologia (Programa Operacional Cie OE ncia,Tecnologia e Inovac -a ì o).
GC Subtyping and HIV Infection in a Spanish Population: No Evidence of an Association between GC Subtypes and AIDS
Human Heredity, 1990
Group-specific component (GC) subtyping was performed by isoelectric focusing in 318 Spanish drug... more Group-specific component (GC) subtyping was performed by isoelectric focusing in 318 Spanish drug users at risk for infection or infected by HIV (85 HIV seronegatives, 111 HIV seropositives without symptoms, 89 seropositives with symptoms, 33 AIDS patients) and 187 healthy individuals. There was no significant association between GC subtypes and susceptibility to HIV infection and/or progression to AIDS.
Forensic Science International, 2006
Infections are considered to be an important cause of unexpected death in children. It has also b... more Infections are considered to be an important cause of unexpected death in children. It has also been assumed that respiratory viruses are involved in the genesis of sudden infant death syndrome (SIDS). The Spanish National Institute of Toxicology and Forensic Sciences act as the forensic reference centre for Spain. We analyse the experience of this centre in the virological study of 64 cases of sudden children death where viral serology, virological cultures, herpesviruses polymerase chain reaction (PCR) and electron microscopy were performed. According to pathological findings, death could only be attributed to an adenovirus infection in one amygdalitis with upper airways stenosis and asphyxia. Human herpes virus 6 (HHV-6) was detected by PCR in one case with pathological findings characteristic of SIDS. Recent infection by respiratory syncytial virus (RSV), Epstein-Barr virus (EBV) and cytomegalovirus (CMV) were also detected. Meanwhile, 85.9% of the cases yielded negative viral results. Twenty-eight infants were finally categorised as SIDS. Pathological findings of infection were detected in 12 patients despite the negativity of viral analyses. Although viral infection is an uncommon cause of sudden children death, a complete microbiological investigation will help to solve the puzzle of SIDS. Definitive guidelines for microbiological analyses need to be updated whilst new pathogens are discovered or new techniques are implemented in order to clarify unsolved cases. #
Factors affecting strontium absorption in drownings
Forensic Science International, 2007
This study examines the effects of age, gender, a cold water medium versus warm water medium, and... more This study examines the effects of age, gender, a cold water medium versus warm water medium, and salinity on strontium levels determined in left ventricular blood in drownings. Significant differences in the amount of strontium absorbed into the bloodstream (p<0.001) were detected between individuals who drowned in fresh water versus those drowning in seawater, and between those drowning in cold water versus warm water (p=0.030). However, no significant differences were noted in the strontium concentrations of left ventricular blood according to gender or age.
Comparison between lung weight and blood strontium in bodies found in seawater
Forensic Science International, 2007
This paper examines the use of lung weight increase as an indicator of seawater drowning compared... more This paper examines the use of lung weight increase as an indicator of seawater drowning compared to the amount of Sr absorbed by the blood. The study population was limited to male victims older than 20 years. Significant differences between cases of drowning and "non-drowning" were detected in terms of the lung-heart weight ratio (L/H) (p<0.001) or lung-body weight ratio (L/B) (p=0.005). However, using lung weight (L), L/H or L/B to distinguish between seawater drownings and saltwater non-drownings some overlap was produced. The factor rendering least overlap was L/B, which also appeared to be non-dependent on the victim's age. Our findings suggest that a value of L/B higher than 19.5 g/kg could be a useful indicator of death by drowning, but that when a lower value is found, additional drowning diagnoses would be needed to establish the manner of death.
Latex agglutination for bacterial antigens and meningococcus PCR: two useful tools in legal sudden deaths
Forensic Science International, 2005
Bacterial infections are considered to be a major cause of sudden deaths. The recognition of infe... more Bacterial infections are considered to be a major cause of sudden deaths. The recognition of infections caused by Neisseria meningitidis is an essential duty of medicolegal offices due to the risk of secondary cases. Since other microorganisms, such as Haemophilus influenzae and Streptococcus pneumoniae, are also involved in infectious sudden deaths, the identification of the pathogen responsible for death is essential in order to establish a positive diagnosis while also preventing secondary meningococcal cases. However, because of the unreliability of culture methods used for autopsy specimens and the fragile nature of the microorganisms, other techniques were used. In this study, the detection of specific antigens of N. meningitidis (serogroups A, B, C, Y and W135), H. influenzae type b, S. pneumoniae and Group B Streptococcus was undertaken in 40 samples from sudden death cases in legal procedures with a latex agglutination test. In addition, a meningococcus polymerase chain reaction (PCR) assay (ctrA, crgA and siaD genes) was also used as a corroboration method for positive N. meningitidis agglutinations. Eleven cases of sudden death were confirmed to be due to meningococcus while one case was confirmed to have been caused by H. influenzae type b fulminant epiglottitis. Rapid laboratory diagnosis of meningococcal infection allowed contacts management and notification to the health authorities. From the point of view of the authors, forensic diagnosis of unascertained deaths should include latex agglutination and meningococcus PCR when a fulminant infection by N. meningitidis or H. influenzae is suspected as well as in deaths where the cause is unclear.
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Papers by Guillermo Vallejo