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Biomedical subjects

Xuming He

Publications and source records attributed to Xuming He.

8 recordsLinked to original sources
PubMed2006

Quantile regression methods for reference growth charts.

Estimation of reference growth curves for children's height and weight has traditionally relied on normal theory to construct families of quantile curves based on samples from the reference population. Age-specific parametric transformation has been used to significantly broaden the applicability of these normal theory methods. Non-parametric quantile regression methods offer a complementary strategy for estimating conditional quantile functions. We compare estimated reference curves for height using the penalized likelihood approach of Cole and Green with quantile regression curves based on data used for modern Finnish reference charts. An advantage of the quantile regression approach is that it is relatively easy to incorporate prior growth and other covariates into the analysis of longitudinal growth data. Quantile specific autoregressive models for unequally spaced measurements are introduced and their application to diagnostic screening is illustrated.

Adolescent↗
PubMed2005

A study of inter-lab and inter-platform agreement of DNA microarray data.

As gene expression profile data from DNA microarrays accumulate rapidly, there is a natural need to compare data across labs and platforms. Comparisons of microarray data can be quite challenging due to data complexity and variability. Different labs may adopt different technology platforms. One may ask about the degree of agreement we can expect from different labs and different platforms. To address this question, we conducted a study of inter-lab and inter-platform agreement of microarray data across three platforms and three labs. The statistical measures of consistency and agreement used in this paper are the Pearson correlation, intraclass correlation, kappa coefficients, and a measure of intra-transcript correlation. The three platforms used in the present paper were Affymetrix GeneChip, custom cDNA arrays, and custom oligo arrays. Using the within-platform variability as a benchmark, we found that these technology platforms exhibited an acceptable level of agreement, but the agreement between two technologies within the same lab was greater than that between two labs using the same technology. The consistency of replicates in each experiment varies from lab to lab. When there is high consistency among replicates, different technologies show good agreement within and across labs using the same RNA samples. On the other hand, the lab effect, especially when confounded with the RNA sample effect, plays a bigger role than the platform effect on data agreement.

Animals↗
PubMed2005

A nationwide survey of physician office visits found that inappropriate antibiotic prescriptions were issued for bacterial respiratory tract infections in ambulatory patients.

OBJECTIVE: Correlations between probabilities of resistance and the frequencies with which antibiotics were prescribed for treating bacterial respiratory infections were examined in a nationwide ambulatory population. STUDY DESIGN AND SETTING: The data of a nationwide probability sample survey of visits to physician offices in the United States in 1999 were used to conduct this study of drug use. A clinical pharmacologist identified antibiotics prescribed during those visits using a large online database. The participating physicians diagnosed the bacterial respiratory infections. An infectious disease expert determined the probabilities of bacterial resistance from a nationwide antibiotic surveillance database. RESULTS: Various bacterial respiratory infections were diagnosed during 6.5% of physician office visits in 1999. One or more antibiotics were prescribed during 51.0% of those visits. The probabilities of resistance to the most frequently prescribed antibiotics varied from 20% to 40% and showed a weak positive correlation with the frequencies of antibiotic prescriptions. CONCLUSION: A significant number of inappropriate antibiotic prescriptions were issued for infections with a high probability of bacterial resistance to the prescribed antibiotics.

Adolescent↗
PubMed2005

Bolus location associated with videofluoroscopic and respirodeglutometric events.

The purpose of the present investigation was to determine the relation between specific events observed with simultaneous videofluoroscopy and respirodeglutometry. The order of occurrence was determined for each of 31 events (18 videofluoroscopic, 13 respirodeglutometric). Using 1 video frame (33.3 ms) as the maximum distance allowed between the average times of 2 events in the same cluster, 8 potential clusters were identified, 3 of which were statistically confirmed based on 90% confidence intervals on the mean time distances between events. Confirmed clusters included the time of (a) complete velar descent and the onset of the small noninspiratory flow (SNIF), (b) full separation of the base of the tongue from the pharyngeal wall and SNIF nadir, complete upper esophageal sphincter closure, and SNIF nadir, and (c) onset of epiglottic return and apnea offset. The onset of respiratory flow occurred within 13 ms after the onset of epiglottic return. Additionally, the percentage of swallows during which the bolus head or tail was located at each of 6 locations was determined for 20 of these events (10 videofluoroscopic, 10 respirodeglutometric). The 6 locations of interest included the oral cavity, base of tongue, valleculae, pyriform sinuses, upper esophageal sphincter, and the esophagus. Lastly, of the 72 swallows performed by these healthy, young adults, 65 (90.3%) were preceded by expiration, and all (100%) were followed by expiration.

Adolescent↗
PubMed2003

Median regression for longitudinal data.

We review and compare three estimators of median regression in linear models with longitudinal data. The estimators are constructed based on well-known ideas of weighting, decorrelating, and the working assumption of independence. Both asymptotic efficiency calculations and finite-sample Monte Carlo studies are used to assess the performance of these estimators. We find that their relative performances depend on the nature of covariates. The estimator under the working assumption of independence is computationally simple and yet has good relative performance when the covariates are invariant over time or when the within-subject correlations are small. Its relative performance in finite samples is also found to be more favourable than suggested by the asymptotic comparisons.

Analgesics↗
PubMed2003

Marginal versus joint Box-Cox transformation with applications to percentile curve construction for IgG subclasses and blood pressures.

When age-specific percentile curves are constructed for several correlated variables, the marginal method of handling one variable at a time has typically been used. We address the question, frequently asked by practitioners, of whether we can achieve efficiency gains by joint estimation. We focus on a simple but common method of Box-Cox transformation and assess the statistical impact of a joint transformation to multivariate normality on the percentile curve estimation for correlated variables. We find that there is little gain from the joint transformation for estimating percentiles around the median but a noticeable reduction in variances is possible for estimating extreme percentiles that are usually of main interest in medical and biological applications. Our study is motivated by problems in constructing percentile charts for IgG subclasses of children and for blood pressures in adult populations, both of which are discussed in the paper as examples, and yet our general findings are applicable to a wide range of other problems.

Adolescent↗
PubMed2002

Inappropriate prescriptions for the aging population of the United States: an analysis of the National Ambulatory Medical Care Survey, 1997.

PURPOSE: Generally, elderly patients in the United States tend to consume more prescriptions than younger adults. The purpose of the study is to examine nationwide prescription patterns for elderly patients who visited physicians' offices in 1997. METHODS: The database of a nationwide sample survey of practicing physicians participating in the National Ambulatory Medical Care Survey, 1997 was used. Inappropriate medicines for the elderly were identified using previously published and widely accepted criteria. RESULTS: During 1997, patients aged 65 years or older made more than 191 million visits to physicians' offices in the United States. Four or more prescriptions per visit were issued with the following frequencies: 17.7% for females; 16.4% for males; 17.0% for Whites, 22.7% for Blacks, and 6.1% for other minorities including American Asians, Indians, Eskimos, Aleuts and Pacific Islanders. The frequencies with which at least one inappropriate medication per visit was prescribed were: 10.8% for females; 8.9% for males; 10.3% for Whites; 9.7% for Blacks; and 1.9% for other minorities. DISCUSSION: Four or more prescriptions issued per visit and inappropriate prescriptions for the elderly in the United States were evident, and may put a vulnerable aging population at risk of adverse drug events.

Aged↗