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PubMed1998

Psychometric evaluation of a Korean Health Assessment Questionnaire for clinical research.

OBJECTIVE: The Health Assessment Questionnaire (HAQ) is a widely used, easily administered functional scale that has high reliability and validity. Although translated versions of HAQ are available, no Korean version exists. Our aim was to translate and confirm the reliability and validity of a Korean language version of the HAQ. METHODS: HAQ was translated into Korean by 3 translators and translated back into English by 3 different translators. Four questions were modified for the Korean culture. Fifty-six consecutive patients with RA were asked to rate the comprehensibility of the questions on a 4 point scale. The comprehensibility (responding with "3 or above") ranged from 76 to 98%. Another 60 consecutive patients with RA were studied for the psychometric properties of the Korean version. RESULTS: The test-retest reliability of the Korean HAQ (KHAQ) yielded an intraclass correlation coefficient of 0.99. The Cronbach standardized alpha was 0.95 among 20 items. For construct validity, the correlation of KHAQ scores with disease severity [tender joint count, swollen joint count, patient's self-assessment of pain, erythrocyte sedimentation rate (ESR), Ritchie Index] was high and statistically significant, except for ESR. The 4 revised items were appropriate expressions of physical function since the correlations between each of the revised items and the first principal component are similar in magnitude to those between the 16 unchanged items and the principal component. CONCLUSION: The reliability and validity of the KHAQ is confirmed. The evaluation of responsiveness of the KHAQ is in progress.

Arthritis, Rheumatoid↗
PubMed2003

Modelling multivariate biomechanical measurements of the spine during a rowing exercise.

OBJECTIVE: To investigate the ability of statistical techniques to detect systematic changes in rowing technique during a rowing session and to discriminate between rowers of different abilities with and without back pain. DESIGN: Statistical techniques were applied to kinematic datasets of elite level rowers, in order to construct an empirical model of the rowing stroke. BACKGROUND: The size and complexity of datasets generated by biomechanical kinematics evaluations has led to opportunities for analysing pathology whilst introducing substantial challenges for statistical analysis. METHODS: Spinal motion and load output of 18 International and National standard competitive rowers were monitored during ergometer rowing sessions. International rower data were used to construct an empirical model of this activity. Linear stroke models were derived using principal components and a generalized cross-validation procedure. Performance characteristics of the identified models were calculated for all rowing groups. The stroke model was applied to distinguishing pattern variations within and between rowers. A multivariate logistic regression analysis was carried out to examine the relationship between stroke model parameters on the incidence of low back pain. RESULTS: 90% of the variability in the data was explained by the first three principal component variables. Stroke models with three basis functions were selected for each variable. The models performed well on the National rowers, providing validation of the models. A 2-variable model showed a significant difference between the rowing stroke characteristics of rowers with and without low back pain (P<0.01). CONCLUSIONS: A parsimonious collection of empirical models effectively describes motion and load characteristics of ergometer rowing. Patterns in rowing technique are found to be strongly associated with the incidence lower back pain. RELEVANCE: Empirical statistical models can be used to track changes in rowing technique, and discriminate between different rowing groups. This may impact rowing training, and rehabilitation.

Biomechanical Phenomena↗
PubMed2003

P300 and genetic risk for schizophrenia.

BACKGROUND: We assessed the suitability of event-related potential frontal and temporoparietal P300 changes as intermediate phenotypes in genetic studies of schizophrenia. We applied a principal component analysis approach based on the notion that P300 abnormalities in siblings of schizophrenic patients may involve a widespread network of relatively weak cortical generators and because an earlier, smaller study that used a topographic analysis of covariance model did not show that localized P300 changes predict risk for schizophrenia. METHODS: P300 changes in 66 schizophrenic patients, 115 healthy siblings of schizophrenic patients, and 89 unrelated controls were studied during a standard auditory oddball paradigm. Principal components were calculated across electrodes, revealing frontal and temporoparietal components for latency and amplitude, respectively. For the frontal and temporoparietal P300 amplitude and latency components, the intraclass correlations (ICCs) between sib-pairs (pairs of unaffected siblings and schizophrenic index patients) and the relative risk ratios (lambda) were determined. RESULTS: Compared with controls, schizophrenic patients and their unaffected siblings showed significant reductions in the temporoparietal P300 amplitude component. Both groups were also characterized by a significantly higher frontal P300 amplitude component. Significant ICCs and increased relative risk ratios were found for the frontal (ICCU = 0.18; P =.04; lambda = 3.4) and temporoparietal (ICCU = 0.24; P =.01; lambda = 1.7) P300 amplitude components. CONCLUSIONS: Temporoparietal P300 amplitude reduction and frontal P300 amplitude increase seem to be quantitative phenotypes associated with increased risk of schizophrenia. Both measures may be useful for increasing the statistical power of genetic studies of schizophrenia.

Adolescent↗
PubMed2004

Integrated methodology for forensic oil spill identification.

A new integrated methodology for forensic oil spill identification is presented. It consists of GC-MS analysis, chromatographic data processing, variable-outlier detection, multivariate data analysis, estimation of uncertainties, and statistical evaluation. The methodology was tested on four groups of diagnostic ratios composed of petroleum biomarkers and ratios within homologous PAH categories. Principal component analysis (PCA) was employed and enabled the simultaneous analysis of many diagnostic ratios. Weathering was taken into account by considering the sampling uncertainties estimated from replicate spill samples. Statistical evaluation ensured an objective matching of oil spill samples with suspected source oils as well as classification into positive match, probable match, and nonmatch. The data analysis is further refined if two or more source oils are classified as probable match by using weighted least squares fitting of the principal components, local PCA models, and additional information relevant to the spill case. The methodology correctly identified the source of two spill samples (i.e., crude oils from Oseberg East and Oseberg Field Centre) and distinguished them from closely related source oils.

Denmark↗
PubMed2005

Classification using functional data analysis for temporal gene expression data.

MOTIVATION: Temporal gene expression profiles provide an important characterization of gene function, as biological systems are predominantly developmental and dynamic. We propose a method of classifying collections of temporal gene expression curves in which individual expression profiles are modeled as independent realizations of a stochastic process. The method uses a recently developed functional logistic regression tool based on functional principal components, aimed at classifying gene expression curves into known gene groups. The number of eigenfunctions in the classifier can be chosen by leave-one-out cross-validation with the aim of minimizing the classification error. RESULTS: We demonstrate that this methodology provides low-error-rate classification for both yeast cell-cycle gene expression profiles and Dictyostelium cell-type specific gene expression patterns. It also works well in simulations. We compare our functional principal components approach with a B-spline implementation of functional discriminant analysis for the yeast cell-cycle data and simulations. This indicates comparative advantages of our approach which uses fewer eigenfunctions/base functions. The proposed methodology is promising for the analysis of temporal gene expression data and beyond. AVAILABILITY: MATLAB programs are available upon request.

Algorithms↗
PubMed2004

Satisfactory cross cultural equivalence of the Dutch WOMAC in patients with hip osteoarthritis waiting for arthroplasty.

BACKGROUND: Cross cultural validity is of vital importance for international comparisons. OBJECTIVE: To investigate the validity of international Dutch-English comparisons when using the Dutch translation of the Western Ontario and McMaster Universities osteoarthritis index (WOMAC). PATIENTS AND METHODS: The dimensionality, reliability, construct validity, and cross cultural equivalence of the Dutch WOMAC in Dutch and Canadian patients waiting for primary total hip arthroplasty was investigated. Unidimensionality and cross cultural equivalence was quantified by principal component and Rasch analysis. Intratest reliability was quantified with Cronbach's alpha, and test-retest reliability with the intraclass correlation coefficient. Construct validity was quantified by correlating sum scores of the Dutch WOMAC, Arthritis Impact Measurement Scales (Dutch AIMS2), Health Assessment Questionnaire (Dutch HAQ), and Harris Hip Score (Dutch HHS). RESULTS: The WOMAC was completed by 180 Dutch and 244 English speaking Canadian patients. Unidimensionality of the Dutch WOMAC was confirmed by principal component and Rasch analysis (good fit for 20/22 items). The intratest reliability of the Dutch WOMAC for pain and physical functioning was 0.88 and 0.96, whereas the test-retest reliability was 0.77 and 0.92, respectively. Dutch WOMAC pain sum score correlated 0.69 with Dutch HAQ pain, and 0.39 with Dutch HHS pain. Dutch WOMAC physical functioning sum score correlated 0.46 with Dutch AIMS2 mobility, 0.62 with Dutch AIMS2 walking and bending, 0.67 with Dutch HAQ disability, and 0.49 with Dutch HHS function. Differential item functioning (DIF) was shown for 6/22 Dutch items. CONCLUSIONS: The Dutch WOMAC permits valid international Dutch-English comparisons after correction for DIF.

Aged↗
PubMed2002

Classification of disease subgroup and correlation with disease severity using magnetic resonance imaging whole-brain histograms: application to magnetization transfer ratios and multiple sclerosis.

This paper presents a new approach to characterize subtle diffuse changes in multiple sclerosis (MS) using histograms derived from magnetization transfer ratio (MTR) images. Two major parts dominate our histogram analysis; 1) Classification of MTR histograms into control and MS subgroups; 2) Correlation with current disability, as measured by the EDSS scale (a measure of disease severity). Two data reduction schemes are used to reduce the complexity of the analysis: linear discriminant analysis (LDA) and principal component analysis (PCA). LDA is better for the classification of MTR histograms as it takes into account the between-class variation. By using LDA, the space of MTR histograms is transformed to the optimal discriminant space for a nearest mean classifier. In contrast, PCA is useful for correlation with current disability as it takes into account the variation within each subgroup in its process. A multiple regression analysis is used to evaluate the multiple correlation of those principal components with the degree of disability in MS. This is the first application of such classification and correlation techniques to magnetic resonance imaging histogram data. Our MTR histogram analysis approach give improved classification success and improved correlation compared with methods that use traditional histogram features such as peak height and peak location.

Adult↗
PubMed2004

Peak bone mineral density at the hip is linked to chromosomes 14q and 15q.

A major determinant of osteoporotic hip fracture is peak hip BMD which is a highly heritable trait. Caucasian American women have lower BMD and higher hip fracture rates than African American women. This study examines linkage of hip BMD in 570 Caucasian sister pairs and 204 African American sister pairs. It compares the results with our published study in a smaller overlapping sample of Caucasian sisters. Hip BMD was measured at neck, trochanter, Ward's, shaft, and total hip. Principal component analysis provided a novel BMD phenotype comprising neck and trochanter, common sites of fracture, and Ward's, site of lowest BMD. A 9 cM genome scan was performed for these phenotypes. Significant linkage was found at chromosomes 14q and 15q. At 14q, the 774 African American and Caucasian sister pairs together yielded the highest LOD score for trochanter (3.5) and at 15q the highest LOD score for femoral neck (4.3). This linkage study in Caucasian and African American healthy premenopausal sisters demonstrates that chromosomes 14q and 15q harbor genes that affect peak bone mass at the hip in women. Principal component had comparable LOD scores with those of the component phenotypes suggesting pleiotropic effects of these genes on hip phenotypes.

Adult↗
PubMed2006

Multivariate data analysis as a fast tool in evaluation of solid state phenomena.

A thorough understanding of solid state properties is of growing importance. It is often necessary to apply multiple techniques offering complementary information to fully understand the solid state behavior of a given compound and the relations between various polymorphic forms. The vast amount of information generated can be overwhelming and the need for more effective data analysis tools is well recognized. The aim of this study was to investigate the use of multivariate data analysis, in particular principal component analysis (PCA), for fast analysis of solid state information. The data sets analyzed covered dehydration phenomena of a set of hydrates followed by variable temperature X-ray powder diffractometry and Raman spectroscopy and the crystallization of amorphous lactose monitored by Raman spectroscopy. Identification of different transitional states upon the dehydration enabled the molecular level interpretation of the structural changes related to the loss of water, as well as interpretation of the phenomena related to the crystallization. The critical temperatures or critical time points were identified easily using the principal component analysis. The variables (diffraction angles or wavenumbers) that changed could be identified by the careful interpretation of the loadings plots. The PCA approach provides an effective tool for fast screening of solid state information.

Anti-Bacterial Agents↗
PubMed2003

Sampling strategy in molecular microbial ecology: influence of soil sample size on DNA fingerprinting analysis of fungal and bacterial communities.

Assessing soil microbial community structure by the use of molecular techniques requires a satisfactory sampling strategy that takes into account the high microbial diversity and the heterogeneous distribution of microorganisms in the soil matrix. The influence of the sample size of three different soil types (sand, silt and clay soils) on the DNA yield and analysis of bacterial and fungal community structure were investigated. Six sample sizes from 0.125 g to 4 g were evaluated. The genetic community structure was assessed by automated ribosomal intergenic spacer analysis (A-RISA fingerprint). Variations between bacterial (B-ARISA) and fungal (F-ARISA) community structure were quantified by using principal component analysis (PCA). DNA yields were positively correlated with the sample size for the sandy and silty soils, suggesting an influence of the sample size on DNA recovery, whereas no correlation was observed in the clay soil. B-ARISA was shown to be consistent between the different sample sizes for each soil type indicating that the sampling procedure has no influence on the assessment of bacterial community structure. On the contrary for F-ARISA profiles, strong variations were observed between replicates of the smaller samples (<1 g). Principal component analysis analysis revealed that sampling aliquots of soil > or =1 g are required to obtain robust and reproducible fingerprinting analysis of the genetic structure of fungal communities. However, the smallest samples could be adequate for the detection of minor populations masked by dominant ones in larger samples. The sampling strategy should therefore be different according to the objectives: rather large soil samples (> or =1 g) for a global description of the genetic community structure, or a large number of small soil samples for a more complete inventory of microbial diversity.

Bacteria↗
PubMed2002

Knee flexors/extensors in gait of elderly and young able-bodied men (II).

In this study the fundamental tasks of muscle activity at the knee during gait in elderly and young able-bodied subjects were identified using principal component analysis (PCA). Role discrepancies between the older and younger subjects for the actions executed by the knee flexors and extensors during the gait cycle were also investigated. The t-test for independent groups was applied to determine significant differences between spatio-temporal and peak muscle moment parameters (P<0.05). PCA as a multivariate classification and curve structure detection method was applied to the sagittal knee muscle moment curves of twenty elderly (72 +/-5.5 years) and twenty young (25 +/- 8.1 years) subjects. The first three principal components (PCs) which accounted for 80% (older) and 93% (younger) of the information were retained for further analysis. Providing stable locomotion was recognised as a major task of the knee in the older subjects, while for the younger subjects the knee contributed to both balance and propulsion. Supporting the body during single limb support should be considered the only common task at the knee level in elderly and young subjects' gait. The lack of muscle power for propulsion might be the reason for not identifying the knee extensor muscle roles in the first three major tasks during elderly gait. Functional asymmetry can be considered the result of a different ordering of the functional roles of the muscles acting at the knee level in elderly and young subjects.

Adolescent↗
PubMed2005

The effects of air pollution and meteorological parameters on respiratory morbidity during the summer in São Paulo City.

Effects of meteorological variables and air pollutants on child respiratory morbidity are investigated during two consecutive summers (December-March 1992/1993 and 1993/1994) at the Metropolitan Area of São Paulo (MASP), Brazil. The MASP, with almost 17 million inhabitants, is considered the most populous region in South America. Due to warmer temperatures, increased rainfall and consequent low levels of air pollutants during the summer compared to winter, less attention has been paid to epidemiological studies during this season, especially in tropical urban areas such as São Paulo. In the present work, principal component analysis (PCA) is applied to medical end environmental data to identify patterns relating child morbidity, meteorological variables and air pollutants during the summer. The following pollutant concentrations are examined: SO2, inhalable particulate matter (PM10), and O3. The meteorological variables investigated are air temperature, water vapor (water vapor density) and solar radiation. Although low correlation between respiratory morbidity and environmental variables are, in general, observed for the entire dataset, the PCA method indicates that child morbidity is positively associated with O3 for the 1992/1993 summer. This pattern is identified in the third principal component (PC3), which explains about 19% of the total variance of all data in this summer. However, the 1993/1994 summer shows a more complex association between both groups, suggesting stronger ties with meteorological variables. Marked changes in synoptic conditions from the end of January to end of March of the 1993/1994 summer seem to have played an important role in modulating respiratory morbidity. A detailed examination of meteorological conditions in that period indicates that prefrontal (postfrontal), hot (cold) and dry (wet) days favored the observed decrease (increase) of respiratory morbidity.

Adolescent↗
PubMed1990

Rotation and translation of the jaw during speech.

A two-dimensional rigid-body model of jaw movement was used to describe jaw opening and closing gestures for vowels and for bilabial and alveolar consonants. Jaw movements were decomposed into three components: (a) rotation about the terminal hinge axis, (b) the horizontal translation of that axis, and (c) the vertical translation of that axis. Data were collected for 3 subjects in two separate recording sessions. Multiple regression analysis was used to examine the relationships among the three jaw movement components. For 2 subjects, but not for the third, an interdependence between jaw rotation and the first principal component of jaw translation, horizontal translation, was observed. For these 2 subjects, the first degree of freedom of jaw movement corresponded to a combination of rotation and the first principal component of jaw translation. For the third subject, the first degree of freedom of jaw movement corresponded to rotation alone. The results of this study, like those of Westbury (1988), indicate that an accurate description of jaw movement during speech requires the recording of two points of jaw movement.

Adult↗
PubMed2005

The state of conservation of painted surfaces in the presence of accelerated ageing processes monitored by use of FT-Raman spectroscopy and multivariate control charts.

A new method has been developed for monitoring the degradation of paintings. Two inorganic pigments (ultramarine blue and red ochre) were blended with linseed oil and spread on canvas. Each canvas was subjected to simulated accelerated ageing in the presence of typical degradation agents (UV radiation and acidic solution). Periodically the painted surfaces were analysed by FT-Raman, to investigate the status of the surface. The data obtained were analysed by principal component analysis (PCA). Finally the Shewhart and cumulative sum control charts based on the relevant principal components (PC) and the so called scores monitoring and residuals tracking (SMART) charts were built. The method based on the use of PC to describe the process was found to enable identification of the presence of relevant modification occurring on the surface of the samples studied.

Journal Article↗
PubMed1995

Signal detection in averaged evoked potentials: Monte Carlo comparison of the sensitivity of different methods.

Many clinical and research applications rely on detecting evoked potential (EP) signal or EP differences between conditions. Statistical methods for objective signal detection should be sensitive to the presence of signal, but must provide the user strict control on tolerated false alarm rate. The respective sensitivities of 6 signal detection methods were compared through several Monte Carlo simulations involving 2 autocorrelation structures, 5% and 1% significance levels, 8, 10 or 12 replications per study, and increasing signal to noise ratio. The signal detection methods compared were: (1) the Record Orthogonality Test by Permutations (ROT-p), a variant of the Residual Orthogonality Test (Achim et al., 1988), that provides an unbiased estimate of the energy of the signal present in the averaged data, (2) the Tsum2 permutation test of Karniski et al. (1994), (3) a Principal Component Analysis method (PC1) consisting of a t test on the weights of the first principal component, (4) multiple t tests on amplitudes with empirical adjustment for global false alarm rate, and (5-6) the test of Guthrie and Buchwald (1991) on length of consecutive t tests significant at P < 0.05 or 0.01 per-test. The first 3 methods did not exceed their nominal false alarm rate and clearly outperformed the last 3, with the ROT-p method being significantly more sensitive than all others under almost all conditions.

Electrophysiology↗
PubMed1995

Validation of a French-language version of the MOS 36-Item Short Form Health Survey (SF-36) in young healthy adults.

The MOS 36-Item Short Form Health Survey (SF-36) is designed to measure 8 dimensions of health in clinical and general population settings. The main aim of this paper was to examine the reliability and validity of this instrument in young adults. A secondary aim was to document the results of a rapid translation procedure of the instrument, to be compared later to the more thorough official French adaptation. The translated survey was answered in 1992 by 1007 residents of Geneva, Switzerland, 18-44 years old, identified from health insurance rolls (82% response rate). Completion rate for all 8 dimensions of health was 95.5%. The instrument demonstrated excellent covergent (100%) and discriminant (98%) validity against pre-set criteria. Interval scaling of responses could be verified in some, but not all, items. Cronbach alpha (reliability) coefficients ranged from 0.76 to 0.92. Factorial analysis yielded 2 principal components, corresponding to mental and physical health. Thirteen of 16 correlations between health dimensions and principal components were within a pre-established range. Validation by independent clinical variables was also, with few exceptions, consistent with theory. Thus the SF-36 retained excellent psychometric properties even when used in a generally very healthy group. The careful but rapid translation procedure used in this study may be an effective alternative to full-scale cultural adaptations when resources are limited.

Adult↗
PubMed2001

Human elbow joint torque is linearly encoded in electromyographic signals from multiple muscles.

When the central nervous system (CNS) develops a muscular activation pattern to accomplish a particular isometric task, it clearly uses information concerning the external task requirements. These task requirements serve as inputs to neural transformations that output muscular activations. However, the nature of the inputs is not exactly known. Electromyographic (EMG) signals from eight muscles spanning the human elbow, as well as the total joint torque, were collected during a submaximal isometric flexion/extension task at a single joint angle. The EMG data, without any torque information, were subjected to principal components analysis. We found that 98% of EMG data variation could be described by two principal components the first resembled the joint torque and the second resembled the sum of the EMG signals from all eight muscles. The findings suggest that the CNS encodes these two quantities during isometric tasks.

Elbow Joint↗
PubMed2003

Using a modified course experience questionnaire (CEQ) to evaluate the innovative teaching of medical communication skills.

SETTING: At the Faculty of Medical Sciences, The University of the West Indies, St Augustine first-year students take two courses in health communication. In the Centre for Medical Sciences Education students completed a course experience questionnaire. This instrument is potentially useful in evaluating innovative programmes and securing support for their development. CONTEXT: The Faculty of Medical Sciences, The University of the West Indies, St Augustine was the first of three campuses to introduce compulsory health communication courses in 1995. Using a modified form of the 25-item course experience questionnaire (CEQ25) (Broomfield & Bligh, 1998) normally employed in overall degree or course evaluation, this study developed a 30-item questionnaire (CEQ30) to test its applicability to the evaluation of medical communication skills teaching MEASURES: In 1997 - 1998 medical, dentistry, veterinary medicine and pharmacy students completed the original short form of the CEQ25 including five items specific to medical communication skills teaching. Students used a five-point Likert scale ranging from one, indicating that they strongly disagreed with the statement, to a score of five, reporting that they strongly agreed with the statement. Principal Components Analysis with Varimax rotation analysed the scale structure of the evaluation tool. RESULTS: The principal components factor analysis of responses (n = 165) broadly confirmed five of Broomfield and Bligh's six factors, but identified a sixth factor in their original instrument (appropriate assessment) that split into two, and a seventh factor, use of available materials and resources. CONCLUSION: The modified CEQ30 is a reliable instrument with which to evaluate a course in medical communication skills, and encourage reflection on teaching and course design. Its use is applicable to medical courses during overall curriculum change and innovation in a medical school.

Adult↗