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PubMed1976

Cluster analysis profiles of suicide attempters.

The author reports the results of a three-stage cluster analysis of data on 298 patients who attempted suicide. Patients were allocated by the analysis to seven identifiable profile types that correlated with six outcome variables. These profiles include data on the social setting and the seriousness of the attempt and judgments about overall functioning and interpersonal conflict as well as the input of the patients' significant others. The author states that these profiles have prognostic significance as well as implications for the treatment of suicide attempters and the education of emotionally involved significant others.

Anxiety↗

PubMed2001

The continuity of depression symptoms: use of cluster analysis for profile identification in patient and student samples.

BACKGROUND: Findings from several sources suggest that depression lies on a continuum whereby mild and severe variants are thought to differ in severity (i.e., quantitatively), but not in kind (i.e., qualitatively). The current study used cluster analysis to extend this work to examination of depression symptom profiles obtained in distressed student 'analogue' samples and clinically depressed samples. METHOD: Patients with major depressive disorder (n = 101) provided seed points for the depressed cluster, and 176 non-distressed university students (Beck Depression Inventory score < or = 8) provided seed points for the non-depressed cluster. The symptom profiles of three levels of analogue depressed samples were then evaluated (BDI > or = 9, BDI > or = 16, and BDI > or = 21). RESULTS: Only 35.4% of BDI > or = 9 analogue respondents were empirically sorted to the depression cluster and the majority were assigned to the non-depressed cluster. The proportion assigned to the depression cluster increased to 70.5% and to 86.2% when higher BDI cutoffs of 16 and 21 were examined, respectively. The DSM-IV depression symptom profile of the BDI > or = 21 group was very similar to the profile defined by clinical patients. LIMITATIONS: The study relied solely on self-report to assess symptom severity. CONCLUSIONS: It is recommended that higher BDI cutoffs be utilized in analogue depression research than is currently common. On quantitative grounds, analogue subjects who were sorted to the clinically defined depression cluster seem to best represent the idea of depression continuity.

Adolescent↗

PubMed1991

Regression and cluster analysis of the acute toxicity of 267 chemicals to six species of biota and the octanol/water partition coefficient.

The acute toxicities of 267 compounds to six aquatic and one terrestrial species were investigated with correlation, principal component and cluster analysis techniques for relationships with each other and with the compounds' octanol/water partition coefficient. Selection of the investigated chemicals was based on the availability of at least three of the following measured parameters: acute (24-h to 96-h) lethal concentrations (LC50) to the fish fathead minnow (Pimephales promelas), the fish goldorfe (Leuciscus idus melanotus), the zooplankter Daphnia magna, the ciliate Tetrahymena pyriformis, and the algae Scenedesmus quadricauda; the (30-min) inhibitory concentrations (EC50) to the luminescent marine bacterium Photobacterium phosphoreum (the Microtox test); the acute oral dose (LD50) for the common Norway rat and the octanol/water partition coefficient (log P or log Kow). The results indicate highly significant correlations between the fathead minnow, goldorfe and Daphnia LC50 and the Photobacterium EC50 concentrations. The cluster and principal components analyses did not detect any clearly defined groups of compounds. The toxicities were also highly collinear with the octanol/water partition coefficients for all species except the rat, where two relationships are indicated, with the division at log P = 2.00.

Animals↗

PubMed2002

Searching for a Gulf War syndrome using cluster analysis.

BACKGROUND: Gulf veterans report medically unexplained symptoms more frequently than non-Gulf veterans did. We examined whether Gulf and non-Gulf veterans could be distinguished by their patterns of symptom reporting. METHOD: A k-means cluster analysis was applied to 500 randomly sampled veterans from each of three United Kingdom military cohorts of veterans; those deployed to the Gulf conflict between 1990 and 1991; to the Bosnia peacekeeping mission between 1992 and 1997; and military personnel who were in active service but not deployed to the Gulf (Era). Sociodemographic, health variables and scores for ten symptom groups were calculated. RESULTS: The gap statistic indicated the five-group solution as one that provided a particularly informative description of the structure in the data. Cluster 1 consisted of low scores for all symptom groups. Cluster 2 had veterans with highest symptom scores for musculoskeletal symptoms and high scores for psychiatric symptoms. Cluster 3 had high scores for psychiatric symptoms and marginally elevated scores for the remaining nine groups symptom groups. Cluster 4 had elevated scores for musculoskeletal symptoms only and cluster 5 was distinguishable from the other clusters in having high scores in all symptom groups, especially psychiatric and musculoskeletal. CONCLUSION: The findings do not support the existence of a unique syndrome affecting a subgroup of Gulf veterans but emphasize the excess of non-specific self-reported ill health in this group.

Bosnia and Herzegovina↗

PubMed2006

How low is too low? Use of cluster analysis to define low levels of mercaptopurine metabolites.

BACKGROUND: To group patients receiving treatment for acute lymphoblastic leukemia (ALL) according to their oral mercaptopurine (6-MP) metabolite levels and to establish cut-off points to screen for potential poor clinical outcome. PROCEDURE: Methodological study using 6-MP metabolite levels from 48 adolescent ALL patients enrolled in a multicenter adherence study. Cluster analysis was the primary analytical technique. We used two validation methods (a split-sampling and a simulation technique) for validating the results. RESULTS: Four clusters were retained in our initial analysis using our first group of patients (n = 27). Three clusters (labeled 1, 2, and 4) exhibited the expected negative correlation between the two metabolites, that is, "high" values of one were associated with "low" values of the other. One cluster (labeled 3) had "low" levels for both TGN and MMP. Five of the 27 adolescents had their 6-MP "held" during the study. Post-hoc examination of the results revealed that all five grouped in Cluster 3 during the time that their medications were stopped, but grouped in other clusters at other times. The median ANC was highest in Cluster 3, consistent with low therapeutic drug levels. Parameters were reproducible with both validation methods. Values below the respective 75th centile for both TGN and MMP in Cluster 3 for the complete sample (n = 48) are suggested as representing a potentially higher risk for relapse. CONCLUSIONS: This study provides an objective method for identifying patients at risk for treatment failure due to suboptimal 6-MP therapy; the clinical significance of this approach should be examined in future studies.

Adolescent↗

PubMed2006

Cluster analysis of the dermal permeability and stratum corneum/solvent partitioning of ten chemicals in twenty-four chemical mixtures in porcine skin.

Assumptions based on absorption from single solvent systems may be inappropriate for risk assessment when chemical mixtures are involved. We used K-means and hierarchical cluster analyses to identify clusters in stratum corneum partitioning and porcine skin permeability datasets that are distinct from each other based on mathematical indices of similarity and dissimilarity. Twenty-four solvent systems consisting of combinations of water, ethanol, propylene glycol, methyl nicotinate and sodium lauryl sulfate were used with 10 solutes, including phenol, p-nitrophenol, pentachlorophenol, methyl parathion, ethyl parathion, chlorpyrifos, fenthion, simazine, atrazine and propazine. Identifying the relationships between solvent systems that have similar effects on dermal absorption formed the bases for hypotheses generation. The determining influence of solvent polarity on the partitioning data structure supported the hypothesis that solvent polarity drives the partitioning of non-polar solutes. Solvent polarity could not be used to predict permeability because solvent effects on diffusivity masked the effects of partitioning on permeability. The consistent influence of the inclusion of propylene glycol in the solvent system supports the hypothesis that over-saturation due to solvent evaporation has a marked effect on permeability. These results demonstrated the potential of using cluster analysis of large datasets to identify consistent solvent and chemical mixture effects.

Animals↗

PubMed2006

Molecular epidemiology and cluster analysis of human listeriosis cases in three U.S. states.

To better understand the transmission and epidemiology of human listeriosis, 647 Listeria monocytogenes isolates obtained from human listeriosis cases in four U.S. locations (Michigan, Ohio, New York State, and New York City) over 61 months (1998 to 2003) were characterized by automated EcoRI ribotyping. A total of 65 ribotypes were differentiated among the characterized isolates; 393, 227, and 24 isolates were classified into lineages I, II, and III, respectively, and 3 isolates were not classified to lineage. The three most common ribotypes (responsible for 39% of all cases) represented L. monocytogenes epidemic clones, each of which had previously been linked to at least two human listeriosis outbreaks. Categorical analyses revealed that ribotypes and lineages were nonrandomly distributed among the four locations. Temporal cluster analysis of cases identified 13 statistically significant temporal subtype clusters, which represented 26% of all cases. Three of these clusters matched previously described human listeriosis outbreaks. Isolates involved in clusters belonged to nine ribotypes. Four, eight, and one cluster were caused by lineages I, II, and III, respectively. The two largest clusters were both caused by the epidemic clone representing ribotype DUP-1044A. Categorical analyses revealed no significant associations between lineage or ribotype and clinical manifestation (central nervous system infection, septicemia, fetal infection, or other infection) or disease outcome (fatal or not fatal). Although human listeriosis cases are caused by isolates belonging to a diversity of EcoRI ribotypes, specific lineage I epidemic clones cause a large number of human listeriosis cases. Many human listeriosis cases can be grouped into statistically significant temporal clusters, including widely distributed and region-specific clusters associated with isolates of various ribotypes. L. monocytogenes lineages and EcoRI ribotypes do not appear to differ in their likelihood of causing different clinical manifestations or mortality.

Adolescent↗

PubMed2006

Target groups for prevention of neck/shoulder and low back disorders: an exploratory cluster analysis of working and living conditions.

Musculoskeletal disorders (MSDs) have a multifactorial etiology. Therefore, a holistic approach to identifying target groups for primary/secondary prevention is essential. In this study, an exploratory person-oriented approach was applied, using cluster analysis of variables related to physical and psychosocial work conditions, and conditions in the private sphere, on a data set of 1,341 Swedish women and men who had not sought care for MSDs the 6 months preceding enrollment in the study. Three groups at risk and five "healthy" groups regarding MSDs were identified. Two of the risk groups had a strained situation regarding psychosocial work conditions or domestic/family conditions, respectively. The majority of individuals in these groups were women. The third risk group had a strained situation regarding both physical and psychosocial work conditions. This group consisted largely of men working in male-dominated jobs. The five healthy groups had low/moderate metabolic demands at work, and all of them having high proportions of subjects with moderate to high education, and fairly even distributions of men and women. In conclusion, the results indicate that gender-specific working and living conditions are associated with an increased risk for MSDs. The identification of these subgroups in the population may facilitate a selective prevention approach.

Adult↗

PubMed1999

Dynamical cluster analysis of cortical fMRI activation.

Localized changes in cortical blood oxygenation during voluntary movements were examined with functional magnetic resonance imaging (fMRI) and evaluated with a new dynamical cluster analysis (DCA) method. fMRI was performed during finger movements with eight subjects on a 1.5-T scanner using single-slice echo planar imaging with a 107-ms repetition time. Clustering based on similarity of the detailed signal time courses requires besides the used distance measure no assumptions about spatial location and extension of activation sites or the shape of the expected activation time course. We discuss the basic requirements on a clustering algorithm for fMRI data. It is shown that with respect to easy adjustment of the quantization error and reproducibility of the results DCA outperforms the standard k-means algorithm. In contrast to currently used clustering methods for fMRI, like k-means or fuzzy k-means, DCA extracts the appropriate number and initial shapes of representative signal time courses from data properties during run time. With DCA we simultaneously calculate a two-dimensional projection of cluster centers (MDS) and data points for online visualization of the results. We describe the new DCA method and show for the well-studied motor task that it detects cortical activation loci and provides additional information by discriminating different shapes and phases of hemodynamic responses. Robustness of activity detection is demonstrated with respect to repeated DCA runs and effects of different data preprocessing are shown. As an example of how DCA enables further analysis we examined activation onset times. In areas SMA, M1, and S1 simultaneous and sequential activation (in the given order) was found.

Cerebral Cortex↗

PubMed1997

Hydrophobic cluster analysis reveals a third chromodomain in the Tetrahymena Pdd1p protein of the chromo superfamily.

The protein Pdd1p (for programmed DNA degradation) links heterochromatin assembly and DNA elimination in Tetrahymena and has recently been identified as a new member of the chromo superfamily that contains two chromodomains. Using the sensitive bidimensional Hydrophobic Cluster Analysis (HCA) method, we have identified a third, highly divergent chromodomain in the Pdd1p sequence. Based on similarity to chromo shadow domains that mediate protein-protein interactions, this newly identified chromodomain may direct the binding of Pdd1p to other proteins. These findings suggest that Pdd1p may be the prototypical member of a new class in the chromo superfamily as all other members contain only one or two chromodomains. The results also demonstrate the power of HCA in identifying relationships which are not detected by conventional methods of sequence analysis.

Amino Acid Sequence↗

PubMed2005

Cluster analysis of normal personality traits in patients with psychogenic nonepileptic seizures.

The literature on patients with psychogenic nonepileptic seizures (PNES) suggests that they are a heterogeneous population. This study addresses this heterogeneity by describing subtypes of PNES based on a cluster analysis of normal personality traits in patients with PNES. In addition, the identified PNES subtypes are further described on dimensions of psychopathology as measured by the Minnesota Multiphasic Personality Inventory, Second Edition (MMPI-2), and cognition. Three personality clusters emerged: (1) very high neuroticism, low extraversion, low openness, high agreeableness, low conscientiousness; (2) average on all domains; (3) very high neuroticism, average extraversion, low openness, low agreeableness, average conscientiousness. Patients in clusters 1 and 3 appear to exhibit more severe psychopathology and a broader range of symptoms than those in cluster 2. Based on NEO-PI-R and MMPI-2 findings, tentative descriptions of the clusters are offered. Cluster 1 comprises "depressed neurotics"; cluster 2, "somatic defenders"; and cluster 3, "activated neurotics." Clusters 1 and 3 also differ significantly on neurocognitive testing, with cluster 1 significantly lower than cluster 3 in memory functioning, while cluster 2 individuals show generally average cognition across domains. These results suggest the existence of personality subtypes in patients with PNES that should be considered in the design of interventions for them.

Analysis of Variance↗

PubMed2001

Conformational space comparison of GnRH and lGnRH-III using molecular dynamics, cluster analysis and Monte Carlo thermodynamic integration.

The conformational space available to GnRH and lGnRH-III was compared using 5.2 ns constant temperature and pressure molecular dynamics simulations with explicit TIP3P solvation and the AMBER v. 5.0 force field. Cluster analysis of both trajectories resulted in two groups of conformations. Results of free energy calculations, in agreement with previous experimental data, indicate that a conformation with a turn from residues 5 through 8 is preferred for GnRH in an aqueous environment. By contrast, a conformation with a helix from residues 2 through 7 with a bend from residues 6 through 10 is preferred for lGnRH-III in an aqueous environment. The side chains of His2 and Trp3 in lGnRH-III occupy different regions of phase space and participate in weakly polar interactions different from those in GnRH. The unique conformational properties of lGnRH-III may account for its specific anti cancer activity.

Animals↗

PubMed1990

Exploratory cluster analysis of behavioral risks for chronic disease and injury: implications for tailoring health promotion services.

Identifying population subgroups with similar behavioral risks could assist in the social marketing of health promotion programs by providing target segments to whom services and outreach could be specifically matched. In this paper we describe an exploratory application of cluster analysis to health behavior data from a representative telephone sample of Michigan adults (n = 2,285). In addition to replication of the cluster solution through cross validation, we found significant between cluster demographic differences further confirming cluster validity. Demographic and risk profiles of four clusters are presented, and key health promotion services appropriate to each cluster are discussed. Although further research on the construct validity of the clusters is critical, we conclude that this approach can be useful in tailoring health promotion messages, materials, and services.

Adolescent↗

PubMed2004

Cluster analysis for the systematic grouping of genuine cocoa butter and cocoa butter equivalent samples based on triglyceride patterns.

The triglyceride profile of cocoa butters (CBs) from different geographical origins, varieties, growing seasons, and a number of cocoa butter equivalents (CBEs) was determined by capillary gas liquid chromatography. Hierarchical cluster analysis was applied to the five main triglycerides of the samples for the ability to find natural groupings among (a) CBs of various provenance and (b) CBE samples of different types. The samples were clustered using Ward's method, and the similarity values of the linkages were represented by dendrograms. The five triglycerides contained adequate information to obtain a meaningful sample differentiation. This information can be used to assess the purity and the origin of the CB sample examined.

Chromatography, Gas↗

PubMed1994

[3-dimensional topography of the optic papilla with laser scanning tomography: clinical correlation of cluster analysis].

BACKGROUND The evaluation of optic disc topography is essential for the clinical diagnosis of primary open angle glaucoma. The purpose of this study was (1) to establish a computerized cluster formation of optic nerve head topography based on quantitative three-dimensional parameter values and (2) to describe the resulting clusters according to morphological appearance and visual fields. PATIENTS AND METHODS 337 optic nerve heads (glaucomatous optic neuropathy (n = 99), glaucoma suspects (n = 159), normals (n = 79) were analyzed using laser scanning tomography. A hierarchical cluster analysis was performed based on standardized variables (optic disc area, rim area, area-ratio, cup depth, cup steepness, height variations along the contour-line). Visual fields were tested by computerized static threshold perimetry. RESULTS A seven cluster solution met the optimizing criteria. The characteristic morphology of the clusters can be described as "normal" (N), "normal, large" (NL), "supernormal" (SN), "pseudonormal" (PN), "glaucoma-like-flat" (GF), "glaucoma-like-steep" (GS) and "macropapillary" (M). Visual fields were normal in 180 eyes. 99 eyes had glaucomatous field defects, 58 eyes revealed isolated relative scotomas < 10 db. Presence and degree of visual field defects varied within the automatically classified optic disc groups considerably. Visual field defects were found in 7.7% (SN), 8.3% (N), 18.8% (NL), 33.3% (M), 37% (PN), 64.7% (GF) and 83.3% (GS) respectively. Pseudonormal discs were characterized by a flattening of the height variations along the disc border. CONCLUSIONS (1) Optic nerve heads may be automatically classified based upon a combination of three-dimensional topographic variables. (2) Analysis of optic disc topography and computerized perimetry are supplementary tools in the evaluation of the glaucoma patient. Visual field defects may be present within any cluster. However, the likelyness of the presence of visual field defects differs considerably among the topometrically defined groups of optic nerve heads. Functional damage is to be expected in association with reduced height variations along the disc border, a small rim area and a steep cupping of the optic nerve head.

Cluster Analysis↗

PubMed1997

The application of multifactorial cluster analysis in the staging of plaques in early multiple sclerosis. Identification and characterization of the primary demyelinating lesion.

Tissues from 13 exceptionally early cases of multiple sclerosis were studied to identify and characterize the primary demyelinating lesion, using a variety of histological and immunocytochemical methods. Multifactorial cluster analysis identified five significantly distinct lesion groups, which showed histological progression from simple microglial lesions, predominating in tissues from the earliest cases, to complex hypercellular fully demyelinated plaques, chiefly associated with cases of intermediate duration. Quiescent lesions showing evidence of remyelination were found at all stages of the disease studied, but hypocellular inactive plaques, were associated with older cases. Evidence is presented that initial demyelination is effected by activated resident microglia. Undegraded myelin is initially enveloped by membranes bearing fixed complexes of immunoglobulin and complement. In contrast with perivenous encephalomyelitis, in which demyelination was dominated by T-cell infiltration, multiple sclerosis lesions of comparable duration and maturity exhibited humoral immune reactions. Parenchymal CD4+ T-cell infiltration developed in association with subsequent plaque maturation. These results emphasize the need for lesion staging when multiple sclerosis tissues are being used in the investigation of pathogenic mechanisms, and suggest that further analysis of the oligoclonal B-cell response may be productive in the search for primary provoking antigens.

Adult↗

PubMed1999

Limited functional grouping of neurons in the motor cortex hand area during individuated finger movements: A cluster analysis.

Primary motor cortex (M1) hand area neurons show patterns of discharge across a set of individuated finger and wrist movements so diverse as to preclude classifying the neurons into functional groups on the basis of simple inspection. We therefore applied methods of cluster analysis to search M1 neuronal populations for groups of neurons with similar patterns of discharge across the set of movements. Populations from each of three monkeys showed a large group of neurons the discharge of which increased for many or all of the movements and a second small group the discharge of which decreased for many or all movements. Two to three other small groups of neurons that discharged more specifically for one or two movements also were found in each monkey, but these groups were less consistent than the groups with broad movement fields. The limited functional grouping of M1 hand area neurons suggests that M1 neurons act as a network of highly diverse elements in controlling individuated finger movements.

Algorithms↗

PubMed1996

Studying multidimensional constructs through cluster analysis.

The analysis of multidimensional constructs presents a challenge. The challenge is to combine the information from the dimensions relating to the construct in a meaningful way. This article examines a complex construct known as the nursing practice environment and describes the use of cluster analysis to combine information from three dimensional measurements to operationalize the construct.

Cluster Analysis↗