Analysis of Longitudinal Twin Data. Basic Model and Applications to Physical Growth Measures

1979 ◽  
Vol 28 (2) ◽  
pp. 93-105 ◽  
Author(s):  
Ronald S. Wilson
Keyword(s):  
Repeated Measures ◽  
Formal Model ◽  
Monozygotic Twins ◽  
Physical Growth ◽  
Twin Data ◽  
Growth Data ◽  
Basic Model ◽  
Test Of Significance ◽  
Longitudinal Twin Data ◽  
Average Size

A formal model is presented for the analysis of longitudinal twin data, based on the underlying analysis-of-variance model for repeated measures. The model is developed in terms of the expected values for the variance components representing twin concordance, and the derivation is provided for computing within-pair (intraclass) correlations, and for estimating the percent of variance explained by each component. The procedures are illustrated with physical growth data extending from birth to six years, and concordance estimates are obtained for average size and for the pattern of spurts and lags in growth. A test of significance is also described for comparing monozygotic twins with dizygotic twins. The procedures are particularly useful for assessing chronogenetic influences on development, especially whether the episodes of acceleration and lag occur in parallel for genetically matched twins. The model may be employed with psychological data also.

Genetic Models of Affective Disorder: Application to Twin Data

1980 ◽  
Vol 29 (4) ◽  
pp. 289-294 ◽  
Author(s):  
Miron Baron
Keyword(s):  
Affective Disorder ◽  
Affective Disorders ◽  
Monozygotic Twins ◽  
Threshold Models ◽  
Twin Data ◽  
Bipolar Illness ◽  
Major Locus ◽  
Unipolar Disorder ◽  
Locus Model ◽  
Multiple Threshold

Twin data on bipolar and unipolar affective disorders are analyzed by multiple threshold models of inheritance. The two illness types are represented in the models on a continuum of genetic–environmental liability in which bipolar illness has a higher liability threshold than unipolar disorder. Autosomal single major locus model provides an acceptable fit to observed concordance rates in monozygotic twins. The multifactorial-polygenic model is rejected.

scholarly journals Multilevel growth curve models that incorporate a random coefficient model for the level 1 variance function

2017 ◽  
Vol 27 (11) ◽  
pp. 3478-3491 ◽  
Author(s):  
Harvey Goldstein ◽  
George Leckie ◽  
Christopher Charlton ◽  
Kate Tilling ◽  
William J Browne
Keyword(s):  
Random Effects ◽  
Repeated Measures ◽  
Random Effect ◽  
Growth Function ◽  
Individual Variability ◽  
Growth Patterns ◽  
Variance Function ◽  
Longitudinal Growth ◽  
Growth Data ◽  
The Mean

Aim To present a flexible model for repeated measures longitudinal growth data within individuals that allows trends over time to incorporate individual-specific random effects. These may reflect the timing of growth events and characterise within-individual variability which can be modelled as a function of age. Subjects and methods A Bayesian model is developed that includes random effects for the mean growth function, an individual age-alignment random effect and random effects for the within-individual variance function. This model is applied to data on boys’ heights from the Edinburgh longitudinal growth study and to repeated weight measurements of a sample of pregnant women in the Avon Longitudinal Study of Parents and Children cohort. Results The mean age at which the growth curves for individual boys are aligned is 11.4 years, corresponding to the mean ‘take off’ age for pubertal growth. The within-individual variance (standard deviation) is found to decrease from 0.24 cm2 (0.50 cm) at 9 years for the ‘average’ boy to 0.07 cm2 (0.25 cm) at 16 years. Change in weight during pregnancy can be characterised by regression splines with random effects that include a large woman-specific random effect for the within-individual variation, which is also correlated with overall weight and weight gain. Conclusions The proposed model provides a useful extension to existing approaches, allowing considerable flexibility in describing within- and between-individual differences in growth patterns.

scholarly journals Growth Trajectories in Genetic Subtypes of Prader–Willi Syndrome

Genes ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 736
Author(s):  
Daisy A. Shepherd ◽  
Niels Vos ◽  
Susan M. Reid ◽  
David E. Godler ◽  
Angela Guzys ◽  
...  
Keyword(s):  
Mixed Models ◽  
Repeated Measures ◽  
Molecular Subtypes ◽  
Growth Trajectories ◽  
Prader Willi Syndrome ◽  
Growth Data ◽  
Expression Of Genes ◽  
Subject Specific ◽  
Data Points ◽  
Autoregressive Correlation

Prader–Willi syndrome (PWS) is a rare disorder caused by the loss of expression of genes on the paternal copy of chromosome 15q11-13. The main molecular subtypes of PWS are the deletion of 15q11-13 and non-deletion, and differences in neurobehavioral phenotype are recognized between the subtypes. This study aimed to investigate growth trajectories in PWS and associations between PWS subtype (deletion vs. non-deletion) and height, weight and body mass index (BMI). Growth data were available for 125 individuals with PWS (63 males, 62 females), of which 72 (57.6%) had the deletion subtype. There was a median of 28 observations per individual (range 2–85), producing 3565 data points distributed from birth to 18 years of age. Linear mixed models with cubic splines, subject-specific random effects and an autoregressive correlation structure were used to model the longitudinal growth data whilst accounting for the nature of repeated measures. Height was similar for males in both PWS subtypes, with non-deletion females being shorter than deletion females for older ages. Weight and BMI were estimated to be higher in the deletion subtype compared to the non-deletion subtype, with the size of difference increasing with advancing age for weight. These results suggest that individuals with deletion PWS are more prone to obesity.

scholarly journals Marginal Adaptation of Implant Prostheses Fabricated by Different Materials in Excessive Crown Height Space Before and After Veneering

2021 ◽  
Author(s):  
Safoura Ghodsi ◽  
Marzieh Alikhasi ◽  
Majid Sahebi ◽  
Vahideh Nazari
Keyword(s):  
Repeated Measures ◽  
Marginal Adaptation ◽  
Crown Height ◽  
Second Molar ◽  
Basic Model ◽  
Nickel Chromium ◽  
Significant Difference ◽  
Before And After ◽  
Marginal Discrepancy ◽  
To Receive

Objectives: This study aimed to investigate the marginal adaptation of implant-supported three-unit fixed restorations fabricated in excessive crown height by various frameworks namely zirconia, nickel-chromium (Ni-Cr) alloy, and Polyetheretherketone (PEEK) before and after veneering. Materials and Methods: A basic model with two implant fixtures was made to receive posterior three-unit fixed partial dentures (second premolar to second molar) in 15 mm crown height. A total of 30 frameworks were fabricated using Ni-Cr, zirconia, and PEEK (n=10). All specimens were veneered and vertical marginal discrepancy was evaluated before and after veneering using a stereomicroscope (×75). The effect of framework material and veneering on marginal discrepancy was evaluated by repeated-measures and one-way ANOVA, and paired t test (α=0.05). Results: There was a significant difference between the groups (P<0.001) before and after veneering. The vertical marginal discrepancy of zirconia frameworks was significantly lower than that of other groups both before and after veneering (P<0.001). Statistical analysis revealed that the veneering process had a significant effect on marginal adaptation (P<0.001). Conclusion: In implant prostheses with excessive crown height, zirconia had the greatest marginal adaptaion significantly, followed by Ni-Cr. Veneering caused a significant increase in marginal discrepancy of all the materials.

Physical Growth in Phenylketonuria: II. Growth of Treated Children in the PKU Collaborative Study From Birth to 4 Years of Age

PEDIATRICS ◽  
1979 ◽  
Vol 63 (5) ◽  
pp. 700-707
Author(s):  
Vanja A. Holm ◽  
Richard A. Kronmal ◽  
Malcolm Williamson ◽  
Alex F. Roche
Keyword(s):  
Collaborative Study ◽  
The United States ◽  
Height Growth ◽  
International Standards ◽  
Physical Growth ◽  
Growth Data ◽  
Normal Children ◽  
Sample Height ◽  
Genetic Endowment ◽  
Diet Management

Height, weight, and head circumference data up to age 4 years are reported for 124 children with phenylketonuria (PKU) who had been started on diet management before 4 months (121 days) of age and who were participating in the Collaborative Study of Children Treated for Phenylketonuria. Growth measurements of both the children and their parents corresponded with national and international standards. The growth of children with PKU was compared also with that of a group of normal children in the United States in whom corresponding longitudinal growth data had been obtained at the Fels Research Institute (FRI). Statistically significant differences between the groups were not noted at any age. However, when these groups were compared on coefficients using curve fitting, a trend toward a greater increase in weight as they became older, noted in both sexes in the PKU study group, was significantly higher (P ≤ .005) in the PKU study girls compared with the FRI sample. Height growth was identical in both groups, and comparison with family data showed that the children with PKU grew as expected for their genetic endowment.

THE ASSESSMENT AND RECORDING OF MEASUREMENTS OF GROWTH OF CHILDREN: REPORT OF A SMALL CONFERENCE

PEDIATRICS ◽  
1973 ◽  
Vol 51 (3) ◽  
pp. 461-466
Author(s):  
George M. Owen
Keyword(s):  
American Academy ◽  
Physical Growth ◽  
Child Health Service ◽  
Growth Data ◽  
American Academy Of Pediatrics ◽  
Physical Measures ◽  
Significant Disease ◽  
Small Conference ◽  
And Child Health ◽  
The U.S

The most widely used standards for height and weight, those of Stuart and Meredith, are still appropriate references, although they do not accurately represent the U.S. child population. New standards based on current measurements of more representative population samples should be substituted and their use promoted. The American Academy of Pediatrics and the Maternal and Child Health Service are currently exploring arrangements to accomplish this goal. Studies should be undertaken to ascertain the effectiveness of routine physical measures for detecting disorders of growth as indicators of significant disease. If measures other than length-height, weight, and head circumference prove meaningful for evaluating physical growth and if more productive interpretations of traditional physical growth data become possible, the American Academy of Pediatrics should disseminate this information and encourage its application through educational programs. Included in such an effort should be development of recording instruments which would increase accuracy, encourage and facilitate use of these measures, and enhance their interpretation.

scholarly journals Latent Curve Analyses of Longitudinal Twin Data Using a Mixed-Effects Biometric Approach

2006 ◽  
Vol 9 (3) ◽  
pp. 343-359 ◽  
Author(s):  
John J. McArdle
Keyword(s):  
Longitudinal Data ◽  
Goodness Of Fit ◽  
Mixed Effects ◽  
Simultaneous Estimation ◽  
Twin Data ◽  
Mixed Effect ◽  
Mixed Effects Modeling ◽  
Curve Model ◽  
Latent Curve ◽  
Longitudinal Twin Data

AbstractIn a recent article McArdle and Prescott (2005) showed how simultaneous estimation of the bio-metric parameters can be easily programmed using current mixed-effects modeling programs (e.g., SAS PROC MIXED). This article extends these concepts to deal with mixed-effect modeling of longitudinal twin data. The biometric basis of a polynomial growth curve model was used by Vandenberg and Falkner (1965) and this general class of longitudinal models was represented in structural equation form as a latent curve model by McArdle (1986). The new mixed-effects modeling approach presented here makes it easy to analyze longitudinal growth-decline models with biometric components based on standard maximum likelihood estimation and standard indices of goodness-of-fit (i.e., χ2, df, εa). The validity of this approach is first checked by the creation of simulated longitudinal twin data followed by numerical analysis using different computer programs (i.e., Mplus, Mx, MIXED, NLMIXED). The practical utility of this approach is examined through the application of these techniques to real longitudinal data from the Swedish Adoption/Twin Study of Aging (Pedersen et al., 2002). This approach generally allows researchers to explore the genetic and nongenetic basis of the latent status and latent changes in longitudinal scores in the absence of measurement error. These results show the mixed-effects approach easily accounts for complex patterns of incomplete longitudinal or twin pair data. The results also show this approach easily allows a variety of complex latent basis curves, such as the use of age-at-testing instead of wave-of-testing. Natural extensions of this mixed-effects longitudinal approach include more intensive studies of the available data, the analysis of categorical longitudinal data, and mixtures of latent growth-survival/ frailty models.

scholarly journals Bacteriostatic Effect of Fresh-cut Spinach on Listeria spp.

HortScience ◽  
1997 ◽  
Vol 32 (3) ◽  
pp. 490A-490
Author(s):  
Isabelle Babic ◽  
Alley E. Watada
Keyword(s):  
Repeated Measures ◽  
Fixed Effects ◽  
Significant Interaction ◽  
Mixed Model ◽  
Inhibitory Effect ◽  
Growth Data ◽  
Bacteriostatic Effect ◽  
Daily Growth ◽  
Freeze Dried ◽  
Fresh Cut

Fresh-cut spinach has been shown to have a bacteriostatic effect on Listeria monocytogenes ATCC 19111 (Babic et al., 1997). A study was undertaken to determine if this effect is noted on other species of Listeria and to determine if the spinach or the natural microorganisms on the spinach was the cause of the bacteriostatic effect. Six species of Listeria was cultivated in pure tryptic soy broth, tryptic soy broth containing freeze-dried spinach powder, or broth containing mesophilic aerobic microorganisms (MAM) isolated from spinach powder. The cultures were incubated at 10°C for 6 days and growth measured daily. Growth data were analyzed as four factor general linear repeated measures mixed model with species, treatment, and day as the fixed effects. The fixed effects showed a significant interaction between treatment × day and day × species. Results indicated that both the spinach and MAM had an inhibitory effect on Listeria as noted by the maximum population at 6 days, which was 8.8 Log10 cfu/ml in control, 6.4 in spinach powder cultures, and 7.4 in mixed cultures (P < 0.05). Of the six Listeria species, three L. monocytogenes were affected similarly whereas the remaining three, particularly L. innocua, were affected differently. In conclusion, the bacteriostatic effect of fresh-cut spinach differs with Listeria species and the native microorganisms play a major role as competitors.

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