Biomedical subjects

W Chen

Publications and source records attributed to W Chen.

At least 181 records · Page 10Linked to original sources

PubMed2001

Frontal lobe dementia with abnormal cholesterol metabolism and heterozygous mutation in sterol 27-hydroxylase gene (CYP27).

Of the primary dementing disorders that cause frontotemporal dementia, the best-known is Pick disease. We report on a 44-year-old woman with progressive frontal lobe dementia and spastic paraplegia. Examination revealed increased serum levels of cholestanol with abnormal cholesterol metabolism and a heterozygous mutation of the sterol 27-hydroxylase gene (CYP27). Biochemical findings were compatible with cerebrotendinous xanthomatosis (CTX); however, the clinical manifestations were very dissimilar. To our knowledge, a symptomatic carrier of this mutation among CTX patients has not been reported. We speculate that the present patient has a previously undescribed neurodegenerative disease related to abnormal cholesterol metabolism with this heterozygous mutation.

Adult↗

PubMed2001

High prevalence of Mycoplasma pneumoniae in intestinal mucosal biopsies from patients with inflammatory bowel disease and controls.

Intestinal microflora are believed to play an important role in the pathogenesis of inflammatory bowel disease (IBD). Mycoplasma have been suggested previously as organisms of ubiquitous distribution with the potential to cause inflammatory diseases, including IBD in susceptible individuals. The aim of this study was to determine the frequency of the presence of M. pneumoniae DNA in intestinal biopsies from patients with IBD and non-IBD controls using a microplate polymerase chain reaction-hybridization assay (PCR-ELISA). A total of 260 endoscopic biopsies (49 from 19 patients with Crohn's disease, 76 from 27 patients with ulcerative colitis, and 135 from 43 non-IBD controls) were used in this study. Overall, M. pneumoniae-specific DNA was detected in 100 endoscopic biopsy samples (38.5%). Among them, the detection rate of M. pneumoniae DNA was significantly higher in biopsies from patients with CD (59.2%) than in those from patients with UC (26.3%) or non-IBD controls (37.7%) (chi2 = 13.65, P < or = 0.001). The high prevalence of M. pneumoniae in both IBD patients and controls suggest this organism is ubiquitous and may persist in the intestinal mucosa. Epidemiological studies in IBD suggest acquisition of some agents early in life probably during epidemics in temperate latitudes. M. pneumoniae could be one of the ubiquitous agents implicated in the pathogenesis of IBD.

Adult↗

PubMed2001

A novel influenza A virus mitochondrial protein that induces cell death.

While searching for alternative reading-frame peptides encoded by influenza A virus that are recognized by CD8+ T cells, we found an abundant immunogenic peptide encoded by the +1 reading frame of PB1. This peptide derives from a novel conserved 87-residue protein, PB1-F2, which has several unusual features compared with other influenza gene products in addition to its mode of translation. These include its absence from some animal (particularly swine) influenza virus isolates, variable expression in individual infected cells, rapid proteasome-dependent degradation and mitochondrial localization. Exposure of cells to a synthetic version of PB1-F2 induces apoptosis, and influenza viruses with targeted mutations that interfere with PB1-F2 expression induce less extensive apoptosis in human monocytic cells than those with intact PB1-F2. We propose that PB1-F2 functions to kill host immune cells responding to influenza virus infection.

Amino Acid Sequence↗

PubMed2001

Searching the Porphyromonas gingivalis genome with peptide fragmentation mass spectra.

An approach is described for genomic database searching based on experimentally observed proteolytic fragments, e.g., isolated from 1D or 2D gels or analyzed directly, that can be applied to unfinished prokaryotic genomic data in the absence of annotations or previously assigned open reading frames (ORFs). This variation on the database search is in contrast to the more familiar use of peptide mass spectral fragmentation data to search fully annotated inferred protein databases, e.g., OWL or SWISS-PROT. We compared the SEQUEST search results from a six reading frame translation of the Porphyromonas gingivalis genome DNA sequence with those from computationally derived ORFs created using publicly available genomics software tools. The ORF approach eliminated many of the artifacts present in output from the six reading frame search. The method was applied to uninterpreted tandem mass spectrometric data derived from proteins secreted by the periodontal pathogen Porphyromonas gingivalis in response to the gingival epithelial cell environment, a model system for the study of host-pathogen interactions relevant to human periodontal disease.

Bacterial Proteins↗

PubMed2001

Eradication of Helicobacter pylori prevents ulcer development in patients with ulcer-like functional dyspepsia.

BACKGROUND: Although the eradication of Helicobacter pylori infection benefits patients with gastric or duodenal ulcers, the value of eradicating the infection in the patients with functional dyspepsia (FD) remains controversial. AIMS: To determine whether eradicating H. pylori can prevent the subsequent development of ulcers or relieve the symptoms of functional dyspepsia patients. METHODS: In a double-blind, placebo-controlled trial, 161 patients infected with H. pylori who had functional dyspepsia were randomly assigned to 7 days of treatment with a lansoprazole-based triple therapy or placebo and then followed for 1 year. The main outcome measures were the development of peptic ulcers and the resolution of symptoms. RESULTS: H. pylori was eradicated in 63 out of 81 patients (78%) in the treatment group and none of the 80 patients (0%) in the placebo group. During the follow-up period, two patients in the treatment group and six patients in the placebo group developed peptic ulcers at repeat endoscopy (2.5% vs. 7.5%; 95% CI: -12 to 2). The reduction in ulcer rates was statistically significant in the 'ulcer-like' sub-group (0% vs. 16.7%; 95% CI: -32 to -2), but not in the 'dysmotility-like' and 'unclassifiable' sub-groups. Regarding symptom response, the resolution rates of symptoms were similar between the treatment and placebo groups (58.0% vs. 55.0%, 95% CI: -12 to 18). Additionally, no significant differences existed in the symptom responses between the treatment and control arms in each of the dyspepsia sub-groups. CONCLUSIONS: Eradicating H. pylori can prevent the subsequent development of peptic ulcers in the patients with 'ulcer-like' functional dyspepsia. However, this approach does not significantly reduce the symptoms of functional dyspepsia patients.

2-Pyridinylmethylsulfinylbenzimidazoles↗

PubMed2001

Helicobacter pylori infection: mechanism of colonization and functional dyspepsia Reduced colonization of gastric mucosa by Helicobacter pylori in mice deficient in interleukin-10.

BACKGROUND AND AIMS: Interleukin-10 (IL-10) is a potent anti-inflammatory and immunoregulatory cytokine. Mice deficient in IL-10 production (IL-10-/-mice) develop a spontaneous chronic enterocolitis, suggesting that IL-10 is an important regulator of the mucosal immune response in vivo. The objective of this study was to determine the role of endogenous IL-10 in the host defense against gastric colonization by Helicobacter pylori by using IL-10-deficient mice. METHODS: The IL-10-/-mice were inoculated intragastrically with a mouse-adapted H. pylori isolate (Sydney Strain 1). Gastric colonization by H. pylori (biopsy urease test and bacterial colony counts), serum levels of H. pylori-specific immunoglobulin (Ig) M, A, G, isotypes of IgG, and the gastric mucosal inflammatory scores were determined 6 weeks after inoculation. Results were compared with those obtained from H. pylori-infected control mice (IL-10+/-mice). RESULTS: The colonization of gastric mucosa by H. pylori was reduced approximately 100-fold (P < 0.0001) in IL-10-/-mice (log10 4.87 +/- 0.26CFU/g tissue) as compared to IL-10+/-mice (log10 6.64 +/- 0.22 CFU/g tissue). Furthermore, IL-10-/-mice infected with H. pylori had significantly higher H. pylori-specific IgA and IgG antibodies in serum (P < or = 0.01), and developed much more severe chronic active gastritis than infected IL-10+/-mice. The median scores of the infiltration of gastric mucosa by mononuclear cells and neutrophils were up to threefold higher in IL-10-/-mice than they were in IL-10+/-mice. CONCLUSION: Our studies suggest that endogenous IL-10 is an inhibitor of the protective immune response to H. pylori infection. Interleukin-10 participates in the downregulation of H. pylori-induced gastric inflammatory responses, which apparently confers a survival advantage to the organism promoting more effective colonization of gastric mucosa.

Animals↗

PubMed2001

Early insulin release effectively improves glucose tolerance: studies in two rodent models of type 2 diabetes mellitus.

AIM: Islet dysfunction, characterized by the loss of an acute insulin secretory response (AIR) to glucose is a well-established pathology of type 2 diabetes mellitus. Using oral insulin secreting agents with very different pharmacodynamic profiles, the present study was undertaken to test the hypothesis that, within the setting of an underlying insulin resistance, changes in the insulin response profile can differentially affect glycaemic control. METHOD: The mildly insulin resistant high-fat fed Sprague Dawley (HF) rat and the very insulin resistant Zucker fatty (fa/fa) rat, chronically fitted with indwelling jugular cannula were subjected to an oral glucose load. Compounds were administered 5 min before the oral glucose load. Nateglinide (Nateg) was administered to elicit only an early insulin secretory response and glipizide (Glip) to elicit a later but greater insulin secretory response. Acetaminophen was used as a marker to assess for potential effects of these compounds on gastric emptying rates. RESULTS: Nateg rapidly increased early insulin release (from -5 to 0) while the effects on total insulin release were similar to those in the controls and glucose excursions were eliminated in both diabetic models with no evidence of sustained hypoglycaemia. Conversely, Glip did not affect early insulin release but increased total insulin release (- 15 to 120 min), but only after the oral glucose load. Glip partially curbed glucose excursions in the mildly insulin resistant HF rodent and was totally ineffective in the very insulin resistant Zucker rat. The differential effects could not be attributed to effects on gastric emptying rates. CONCLUSION: These data support the importance of early insulin release in type 2 diabetes mellitus and indicate that, independent of the level of insulin resistance, stimulating insulin release early and briefly provides for more effective and tighter glycaemic control than increasing insulin exposure to a greater magnitude later.

Animals↗

PubMed2001

Neurons reduce glial responses to lipopolysaccharide (LPS) and prevent injury of microglial cells from over-activation by LPS.

The microenvironment of the CNS has been considered to tonically inhibit glial activities. It has been shown that glia become activated where neuronal death occurs in the aging brain. We have previously demonstrated that neurons tonically inhibit glial activities including their responses to the bacterial endotoxin lipopolysaccharide (LPS). It is not clear whether activation of glia, especially microglia in the aging brain, is the consequence of disinhibition due to neuronal death. This study was designed to determine if glia regain their responsiveness to LPS once the neurons have died in aged cultures. When cultured alone, glia from postnatal day one rat mesencephalons stimulated with LPS (0.1-1000 ng/mL) produced both nitric oxide (NO) and tumor necrosis factor alpha (TNFalpha), yielding a sigmoid and a bell-shaped curve, respectively. When neuron-containing cultures were prepared from embryonic day 14/15 mesencephalons, the shape of the dose-response curve for NO was monotonic and the bell-shaped curve for TNFalpha production was shifted to the right. After 1 month of culture under conditions where neurons die, the production curves for NO and TNFalpha in LPS-stimulated glia shifted back to the left compared to mixed neuron-glia cultures. Immunostaining of rat microglia for the marker CR3 (the receptor for complement component C3) demonstrated that high concentrations of LPS (1 microg/mL) reduced the number of microglia in mixed-glial cultures. In contrast, reduction of CR3 immunostaining was not observed in LPS-stimulated mixed neuron-glia cultures. Taken together, the results demonstrate that disinhibition of the glial response to LPS occurs after neurons die in aged cultures. Once neurons have died, the responsiveness of glia to LPS is restored. Neurons prevented injury to microglia by reducing their responsiveness to LPS. This study broadens our understanding of the ways in which the CNS microenvironment affects cerebral inflammation.

Animals↗

PubMed2001

Molecular cloning and characterization of hNP22: a gene up-regulated in human alcoholic brain.

An improved differential display technique was used to search for changes in gene expression in the superior frontal cortex of alcoholics. A cDNA fragment was retrieved and cloned. Further sequence of the cDNA was determined from 5' RACE and screening of a human brain cDNA library. The gene was named hNP22 (human neuronal protein 22). The deduced protein sequence of hNP22 has an estimated molecular mass of 22.4 kDa with a putative calcium-binding site, and phosphorylation sites for casein kinase II and protein kinase C. The deduced amino acid sequence of hNP22 shares homology (from 67% to 42%) with four other proteins, SM22alpha, calponin, myophilin and mp20. Sequence homology suggests a potential interaction of hNP22 with cytoskeletal elements. hNP22 mRNA was expressed in various brain regions but in alcoholics, greater mRNA expression occurred in the superior frontal cortex, but not in the primary motor cortex or cerebellum. The results suggest that hNP22 may have a role in alcohol-related adaptations and may mediate regulatory signal transduction pathways in neurones.

Adult↗

PubMed2001

Melanocortin-1 receptor genotype is a risk factor for basal and squamous cell carcinoma.

MC1R gene variants have previously been associated with red hair and fair skin color, moreover skin ultraviolet sensitivity and a strong association with melanoma has been demonstrated for three variant alleles that are active in influencing pigmentation: Arg151Cys, Arg160Trp, and Asp294His. This study has confirmed these pigmentary associations with MC1R genotype in a collection of 220 individuals drawn from the Nambour community in Queensland, Australia, 111 of whom were at high risk and 109 at low risk of basal cell carcinoma and squamous cell carcinoma. Comparative allele frequencies for nine MC1R variants that have been reported in the Caucasian population were determined for these two groups, and an association between prevalence of basal cell carcinoma, squamous cell carcinoma, solar keratosis and the same three active MC1R variant alleles was demonstrated [odds ratio = 3.15 95% CI (1.7, 5.82)]. Three other commonly occurring variant alleles: Val60Leu, Val92Met, and Arg163Gln were identified as having a minimal impact on pigmentation phenotype as well as basal cell carcinoma and squamous cell carcinoma risk. A significant heterozygote effect was demonstrated where individuals carrying a single MC1R variant allele were more likely to have fair and sun sensitive skin as well as carriage of a solar lesion when compared with those individuals with a consensus MC1R genotype. After adjusting for the effects of pigmentation on the association between MC1R variant alleles and basal cell carcinoma and squamous cell carcinoma risk, the association persisted, confirming that presence of at least one variant allele remains informative in terms of predicting risk for developing a solar-induced skin lesion beyond that information wained through observation of pigmentation phenotype.

Alleles↗

PubMed2001

Methodology standards associated with quality reporting in clinical studies in pediatric surgery journals.

BACKGROUND/PURPOSE: Reports of clinical trials often lack adequate descriptions of design and analysis; recent attention has focused on improving this omission so readers can properly assess the strength of the findings and draw their own conclusions. Similar analysis of study design and methodologic standards associated with quality reporting has not been carried out for pediatric surgery journals. METHODS: All studies (n = 642) published in 1998 in Journal of Pediatric Surgery (JPS) and Pediatric Surgery International (PSI), were reviewed for demographic data and study design. The frequency of reporting of 11 basic elements of design and analysis was evaluated in randomized clinical trials (RCT), nonrandomized clinical trials (NRCT), and retrospective cohorts (RC) from JPS by consensus of 2 assessors. RESULTS: Of the 642 studies, 17% of articles (111 of 642) were classified as clinical studies. Sixty-three were comparative studies and consisted of RC (n = 48), NRCT (n = 12), and RCT (n = 3). Two-thirds of articles published were either case reports or case series (431 of 642), and 16% were basic science articles. Demographic analysis showed a wide range of topics addressed, 4 authors per article, and multiple country of origin of authors. More than 66% of all RCT in JPS reported on eligibility criteria, admission before allocation, random allocation, method of randomization, patients' blindness to treatment, treatment complications, statistical analyses, statistical methods, loss to follow-up, and statistical methods; 2 elements of design and analysis, however, were poorly reported: blind assessment of outcome (33%) and power (17%). CONCLUSIONS: There were few randomized, controlled trials in pediatric surgery journals, and further attention should be given to evaluate the causal factors. Nine elements of quality reporting were well reported; however, 2 others were poorly reported; this may improve if editors of pediatric surgical journals provide authors with guidelines on how to report clinical trial design and analysis.

Authorship↗

PubMed2001

Trends of lipoprotein variables from childhood to adulthood in offspring of parents with coronary heart disease: the Bogalusa Heart Study.

Although dyslipidemia among offspring of parents with coronary heart disease (CHD) has been known, the development of this adverse relationship with respect to specific lipoprotein variables from childhood to young adulthood has not been elucidated. This aspect was examined in a young adult cohort with (n = 271) and without (n = 805) a parental history of CHD followed longitudinally since childhood by repeated surveys from 1973 to 1991. Trends in fasting lipoprotein variables by parental CHD status were assessed by Lowess smoothing curve and Generalized Estimating Equations (GEE). In multivariate analyses adjusted for race and sex, parental CHD associated positively with low-density lipoprotein cholesterol (LDL-C, P <.01) and triglycerides (P <.05) mainly at the young adulthood age, whereas a positive association was noted with very-low-density lipoprotein cholesterol (VLDL-C) during both childhood and young adulthood (P <.05). The positive association between parental CHD and LDL-C in young adulthood persisted independently of body mass index (BMI) and fasting insulin, but disappeared when fasting glucose was added to the model. With respect to triglycerides and VLDL-C, inclusion of BMI, insulin, and/or glucose eliminated the adverse association with parental CHD. These observations suggest that parental CHD is just one more explanatory variable that loses its partial contribution to lipoprotein profiles in their offspring when other strongly interrelated contributory variables such as age, body fatness, and measures of glucose homeostasis are taken into account. Information on these risk variables in conjunction with parental or family history of CHD may enhance the potential of CHD risk assessment in youth.

Adolescent↗

PubMed2001

Increased serum levels of eotaxin in patients with inflammatory bowel disease.

BACKGROUND: The CC-chemokines eotaxin and eotaxin-2, produced by epithelial and phagocytic cells, are potent and selective chemoattractants for eosinophils and basophils. The eosinophil is a potent inflammatory cell thought to play an important role in the pathogenesis of inflammatory bowel disease (IBD). In this study we investigated the serum concentrations of eotaxin and eotaxin-2 in patients with Crohn disease and ulcerative colitis. METHODS: Thirty-one patients with Crohn disease, 35 patients with ulcerative colitis and 41 control patients were studied. Eotaxin and eotaxin-2 serum levels were measured with solid phase sandwich enzyme-linked immunosorbent assays. RESULTS: Significantly increased serum eotaxin levels were observed in both patients with Crohn disease (289.4+/-591.5 pg/ml) and ulcerative colitis (207.0+/-243.4 pg/ml) when compared with controls (138.0+/-107.8 pg/ml) (P < 0.01). Moreover, patients with active Crohn disease and ulcerative colitis showed significantly higher serum eotaxin levels than patients with quiescent disease (434.0+/-776.8 pg/ml versus 113.8+/-65.4 pg/ml in Crohn disease and 295.7+/-337.1 versus 121.2+/-91.9 pg/ml in ulcerative colitis, P < 0.05). In contrast, there was no significant difference in eotaxin-2 serum levels among patients with Crohn disease (863.5+/-448.2 pg/ml), ulcerative colitis (1028.3+/-431.4 pg/ml) and controls (981.4+/-539.4 pg/ml). CONCLUSIONS: Eotaxin is significantly increased in serum of patients with active Crohn disease and ulcerative colitis, suggesting that this cytokine may play a role in the pathogenesis of IBD.

Adolescent↗

PubMed2001

Description of an expert teacher's constructivist-oriented teaching: engaging students' critical thinking in learning creative dance.

The focus of this study was to investigate how an expert teacher implemented constructivist-oriented teaching strategies to engage students'critical thinking skills in learning creative dance. The data were collected through videotaping 16 creative dance lessons taught by an expert teacher to 2 kindergarten, 2 first-grade, and 4 third-grade classes and conducting two formal interviews and several informal interviews with the teacher. In addition, one group interview was conducted with 4 kindergarten students, 4 first-grade students, and 8 third-grade students. The three salient themes were: (a) relating students' knowledge and ideas to lessons to spark dispositions, (b) encouraging and facilitating students' inquiries and creative products, and (c) engaging students' metacognition in refining the quality of dance movement.

Child↗

PubMed2001

Pharmaceutical cost-containment policy: experiences in Shanghai, China.

BACKGROUND: In the decade after 1983, the annual growth rate of drug expenditure was about four times as high as that of per capita gross domestic product (GDP) in Shanghai. In 1993 and 1994, a drug list policy and hospital revenue capping policy were introduced in Shanghai to contain drug expenditure. We studied the impact of these two policies, as a model for similar policies in other parts of China and elsewhere. METHODS: Quarterly drug expenditure data were collected from 1992 to 1996 and more detailed drug expenditure flow was obtained at seven selected hospitals. Twelve focus group discussions were organized to obtain opinions from all stakeholders. RESULTS: The research findings showed a dramatic and continuing decline in the growth rates of total medical and drug expenditures after the implementation of the two policies. The proportion of total medical expenditure attributable to drugs declined from 67% in 1992 to 51% in 1996. The annual growth rate of drug expenditure per ambulatory visit and per bed-day was reduced as well. Drug revenue as a proportion of total hospital revenue declined gradually in all seven hospitals. The two policies did not alter the equity of drug utilization between the insured and non-insured. The government, insurance authority and state-owned drug enterprises all favoured the new policies, while hospital administrators, professionals, joint venture and foreign manufacturers wished for the reimbursement mechanisms to be improved, for retention of their freedom of choice, and for the drug list to be further expanded. CONCLUSIONS: The drug list and capping policies in Shanghai appear to have achieved their objectives of containing the escalation of drug expenditure and improving the rational use of drugs without loss of equity. The underlying causes of the escalation of drug expenditure in China need to be further elucidated.

Ambulatory Care↗

PubMed2001

Comparison of surgical management of thoracic esophageal carcinoma between two referral centers in Japan and China.

BACKGROUND: Comparison was made between two referral centers, the National Cancer Center Hospital (NCCH) in Japan and Shanghai Chest Hospital (SCH) in China. The aim was to detect the possible differences between surgical management of thoracic esophageal carcinoma in these two countries and to shed some light on how to improve the therapeutic outcomes at similar institutions. METHODS: A total of 98 patients (50 from NCCH and 48 from SCH) with squamous cell carcinoma of the thoracic esophagus treated by a single surgeon at either center during January 1997 to July 1999 were retrospectively reviewed. RESULTS: Lugol staining and endoscopic ultrasonography were applied routinely at NCCH only. More early diseases, multiple lesions and synchronous tumors of the digestive tract were detected in the NCCH group than in the SCH group. Significantly more stations of lymph nodes were dissected and higher metastatic rates to certain stations were found after more extensive lymphadenectomy in the NCCH group. Operation time was prolonged with significantly more postoperative complication but amount of blood loss or in-hospital mortality was not increased. There was a tendency toward better survival in the NCCH group at 2-year follow-up (70.9% NCCH vs. 56.2% SCH, p = 0.052). CONCLUSIONS: Lugol staining is useful in detecting early diseases or multiple lesions and endoscopic ultrasonography in increasing the knowledge of preoperative evaluation and thus should be recommended. Attention should be paid to more thorough lymph node dissection, especially those lymph node stations with high metastatic rates within the chest and the abdomen and meanwhile avoiding major postoperative complications, so as to improve further the accuracy of tumor staging and therapeutic outcome.

Carcinoma, Squamous Cell↗

PubMed2001

Release of flexors and intrinsic muscles for finger spasticity in cerebral palsy.

Between April 1987 and March 1996, 32 deformed hands of 31 patients with cerebral palsy were treated with combined release of the flexor digitorum profundus, flexor digitorum superficialis, and intrinsic muscles. Of these 31 patients, 26 patients (27 hands) were followed up after treatment. Improvements were evaluated by the modified classification of Zancolli et al, the classification of House et al, the object handling score, and the activity of daily living score. Improvements of more than one level on an average were observed in the modified classification of Zancolli et al and the classification of House et al. The ability to grasp, pinch, and release increased with improvement of 2.5 points in the object handling score, and activities of daily living were enhanced with improvement of 2.4 points. The fine motor skills could be facilitated, and dexterity was restored in most patients.

Adolescent↗

PubMed2001

Multivariate matching and bias reduction in the surgical outcomes study.

BACKGROUND: Outcomes studies often need a level of detail that is not present in administrative data, therefore requiring abstraction of medical charts. Case-control methods may be used to improve statistical power and reduce abstraction costs, but limitations of exact matching often preclude the use of many covariates. Unlike exact matching, multivariate matching may allow cases to be matched simultaneously on hundreds of covariates. OBJECTIVES: To develop multivariate matched case-control pairs in a study of death after surgery in the Medicare population. RESEARCH DESIGN: Using 830 randomly selected index cases of patients who died within 60 days from admission, controls were found who did not die within that time period, matching on risk for death and other patient characteristics with up to 173 variables used simultaneously in the matching algorithms. SUBJECTS: General and orthopedic Medicare surgical cases in Pennsylvania from 1995 to 1996. Controls were either selected from across the entire state (108,765 possible subjects), or from within the same hospital as the case. MEASURES: Percent bias reduction and the average difference between cases and controls in units of standard deviations. RESULTS: Matched controls were far more similar to cases (deaths) upon admission to the hospital than typical patients, both in statewide and within hospital matches. Bias reduction was usually greater than 50% and often approached 100%. The difference between cases and matched controls for most variables was usually below 0.2 SD. CONCLUSIONS: Multivariate matching methods may aid in conducting studies with Medicare claims records by improving the quality of matches, thereby achieving a better understanding of the etiology of outcomes.

Aged↗