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I Y Guo

Publications and source records attributed to I Y Guo.

10 recordsLinked to original sources
PubMed1995

PC program extending the Potthoff-Roy longitudinal data analysis model to allow missing data: Kleinbaum's method.

Potthoff and Roy (Biometrika, 51 (1964) 313-326) generalized the multivariate analysis of variance model into a form that is especially useful for the study of longitudinal growth curve data. Applications of this method have, however, been limited by the requirement that each case in the sample be measured at the same set of time points, i.e. there can be no missing data. In this paper we describe, illustrate, and make available a user-friendly, interactive PC program implementing Kleinbaum's (J Mult Anal, 3 (1973) 117-124) extension of the Potthoff-Roy model to allow incomplete measurement sequences. These missing data are permitted to arise either randomly or by design as in mixed longitudinal studies.

Analysis of Variance↗
PubMed1994

A PC program for computing confidence bands for average and individual growth curves.

Dawson et al. (Am. J. Med. Genet. 7, 529-536, 1980) developed a procedure for constructing confidence bands for both average and individual growth curves which may be of considerable value in the study of growth and development. This paper describes their method for constructing, and provides a menu-driven GAUSS386i program for computing these confidence bands. It is demonstrated how these bands are useful for both the diagnosis and prognostication of growth patterns with known levels of confidence. It is assumed that the study is planned so that individuals will be measured at the same times, but missing data are allowed.

Confidence Intervals↗
PubMed1994

PC program for growth prediction in the two-stage polynomial growth curve model.

We consider the problem of growth prediction in the context of the two-stage (or random coefficients) one-sample polynomial growth curve model and provide a PC program, written in GAUSS386i, to perform the associated computations. The problem considered is that of estimating the value of the measurement under consideration for a 'new' individual at the Tth time point given measurements on that individual at T-1 previous points in time and the values of the measurement on N 'similar' individuals at all T time points. The times of measurement t1, t2, ..., tT need not be equally spaced, but we assume that each of the N individuals comprising the normative sample were measured at these times. The method and the program are illustrated using the data set previously considered (Schneiderman and Kowalski, Am J Phys Anthrop, 67 (1985) 323-333) consisting of mandibular ramus height measurements (in mm) for 12 male rhesus monkeys at T = 5 yearly intervals (coded 1, 2, 3, 4, and 5). Results are compared with those obtained under a less restrictive set of assumptions concerning the covariance matrix of the observations than is made in the context of the two-stage model. It is seen that the accuracies of prediction of the two methods, for this and other data sets, are quite close, suggesting that the less restrictive model may be preferred in many situations.

Animals↗
PubMed1994

Implementation of exact and approximate randomization tests for polynomial growth curves.

Two stand-alone, menu-driven PC programs, written in GAUSS386i, which compare groups of growth curves in a completely randomized design using either (a) exact or (b) approximate randomization tests, are described, illustrated, and made available to interested readers. The programs accommodate missing data in the context of studies planned to have common times of measurement, but where some of the measurement sequences are incomplete. The measurement whose growth is being monitored need not have a Gaussian distribution. We consider the hypothesis that the mean growth curves in G groups are the same; and either compute the exact P value (exact test), or estimate, and provide a confidence interval for, the P value (approximate test).

Algorithms↗
PubMed1994

Ultrasonic root-end preparation. Part 1. SEM analysis.

Preparations of apical cavities in resected root ends using rotary burs, with and without citric acid rinse, and ultrasonic tips were compared based on the presence or absence of superficial debris and smear layer. Three groups of 20 extracted teeth each were prepared as follows; I, a size 010 round bur was used to prepare an apical cavity 2-3 mm down the long axis of the root; II, treatment as per group I followed by a 60-s rinse with a solution of 10:3 (10% citric acid, 3% Fe2Cl3); and III, an ultrasonic retrotip was used to prepare a 2-3 mm deep apical cavity. Roots were grooved longitudinally, split and prepared for SEM analysis at x100 and x780 magnification. Examiners were calibrated to a standardized grading system. Extensive statistical analyses indicated statistically significant differences within and among the groups (P < 0.05). Root-end preparation with a bur created a heavy smear layer at all levels of the preparation. This layer was partially removed during ultrasonic preparation in the apical two-thirds. A greater removal of the smear layer was achieved with the citric acid rinse (P < 0.05). Coronally, root-end preparations were contaminated with moderate to heavy amounts of debris with all techniques.

Citrates↗
PubMed1994

A PC program for diagnosing abnormal growth, growth velocity and acceleration from longitudinal observations.

A PC program, written in GAUSS386i, implementing Zerbe's (Growth, 43 (1979) 263-272) procedure for diagnosis on the basis of longitudinal data is described, illustrated and made available to interested readers. Given longitudinal observations on N normal individuals, this technique can be used to characterize normal growth, velocity and acceleration, and to determine whether or not a new individual can be considered normal with respect to any or all of these parameters. Missing data are allowed, and there is no requirement that the variable whose growth is being monitored has a normal distribution. The method and program are illustrated using a data set with a substantial amount of missing data. Information on obtaining a copy of the program and hardware requirements are given in the Appendix.

Algorithms↗
PubMed1994

A PC program for computing McMahan's tracking indices from one-sample longitudinal data sets.

Tracking refers to regular, predictable growth behavior. Most definitions of the term are related to the idea that tracking occurs to the extent that individuals' repeated measurements maintain their relative positions in the distribution of the measurement whose growth is being monitored as that distribution changes over time. In this paper we describe four indices of tracking, all due to McMahan (Biometrics, 37 (1981) 447-455), which may be used to measure the extent to which a given longitudinal sample exhibits this 'regular behavior,' and we provide a program, written in GAUSS386i, for performing the associated computations. An example is given, and the values of McMahan's indices are compared to several alternative measures of tracking.

Algorithms↗
PubMed1993

Handling characteristics of gallium alloy for dental restoration.

The handling characteristics of a gallium alloy (Gallium Alloy GF) were compared to those of a spherical high-copper amalgam (Tytin). Ten dentists each restored four identical MO preparations in acrylic typodont teeth (no. 30), two with amalgam and two with gallium alloy. Each restoration was evaluated immediately following completion by the operator for six clinically relevant criteria. Each criterion was scored between 1 and 5, where 1 = very poor, 2 = poor, 3 = fair, 4 = good, and 5 = very good. Three two-sided Mann-Whitney tests were used to compare the median scores for significant differences (P < 0.05). The first test indicated no significant difference between scores for the first- and second-placed restorations, within criteria and within alloy type (n = 10). The second test indicated a significant difference between amalgam and gallium alloy, within criteria and within restoration sequence (n = 10), for each criterion except resistance to fracture during removal of the matrix band. The third test indicated a significant difference between amalgam and gallium alloy, within each criteria, combining scores for first- and second-placed restorations (n = 20). During simulated clinical placement, amalgam was rated significantly higher than gallium alloy in each handling characteristic evaluated.

Dental Alloys↗
PubMedDate not supplied

The effect of glutaraldehyde pulpotomy treatment on pulpal enzymes.

The enzymes lactate dehydrogenase (LD), succinate dehydrogenase (SD), alkaline phosphatase (AP), and glucose-6-phosphate dehydrogenase (G-6-PD) were evaluated at specific locations in pulp tissue following glutaraldehyde pulpotomies. Pulpotomies were performed on maxillary first molars in 40 rats after sacrifice at times 0, 24 hr, seven days, or one month, and experimental teeth were treated with 6% buffered glutaraldehyde. Teeth were prepared for frozen sectioning and the sections were subjected to incubation media to detect each enzyme. Significant differences were found regarding the location of staining and the time intervals at which stain was present or absent. Staining for LD and AP was the most intense throughout the four observation time periods, though staining for these enzymes as well as for G-6-PD had begun to diminish by day seven in the coronal thirds. Staining was completely absent in the coronal thirds at one month but remained in the middle and apical thirds throughout one month. SD was the only enzyme that was totally absent in the coronal third at seven days and totally absent in the middle third at one month. These findings suggest that LD, AP, and the biochemical mechanisms that they represent remain active longer than SD and G-6-PD following exposure to glutaraldehyde. This information is important in identifying mechanisms that are important for repair, healing, and recovery following pulpal injury.

Alkaline Phosphatase↗