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PubMed2003

Genetic Analysis Workshop 13: simulated longitudinal data on families for a system of oligogenic traits.

The Genetic Analysis Workshop 13 simulated data aimed to mimic the major features of the real Framingham Heart Study data that formed Problem 1, but under a known inheritance model and with 100 replicates, so as to allow evaluation of the statistical properties of various methods. The pedigrees used were the 330 real pedigree structures (comprising 4692 individuals) with some minor changes to protect confidentiality. Fifty trait genes and 399 microsatellite markers were simulated by gene dropping on 22 autosomal chromosomes. Assuming random ascertainment of families, a system of eight longitudinal quantitative traits (designed to be similar to those in the real data) was generated with a wide range of heritabilities, including some pleiotropic and interactive effects. Genes could affect either the baseline level or the rate of change of the phenotype. Hypertension diagnosis and treatment were simulated with treatment availability, compliance, and efficacy depending on calendar year. Nongenetic traits of smoking and alcohol were generated as covariates for other traits. Death was simulated as a hazard rate depending upon age, sex, smoking, cholesterol, and systolic blood pressure. After the complete data were simulated, missing data indicators were generated based on logistic models fitted to the real data, involving the subject's history of previous missing values, together with that of their spouses, parents, siblings, and offspring, as well as marital status, only-child indicators, current value at certain simulated traits, and the data collection pattern on the cohort into which each subject was ascertained.

Adult↗
PubMedDate not supplied

Age changes in adult stature: trend estimation from mixed longitudinal data.

Although it is widely accepted that persons become shorter as they grow older, most estimates of the rate of decline are based largely on cross-sectional studies and are confounded by secular changes and individual variation. The present study uses a mixed series of longitudinal physical measurements, obtained by the Busselton Population Studies Group, for nearly the entire adult population of Busselton, Western Australia. All persons in the sample who had a minimum of three measures at 3-year intervals are included in our analysis, regardless of health. Random regressions analysis of the individual height and age data is used to estimate the expected rate of decline of stature with age. A significant sex difference was found, with females declining at a greater rate than males, particularly after the age of 40.

Adolescent↗
PubMed1981

[Longitudinal data of physical growth of healthy children. Lengths of trunk, hand, forearm, upper arm, whole arm, lower leg, thigh and whole leg of children aged 2,5 to 15 years. (author's transl)].

From 1968-78 a longitudinal study was performed concerning development of lengths of trunk, hand, forearm, upper arm, whole arm, lower leg, thigh and whole leg in 709 healthy boys and 711 girls aged 2,5 to 15 years. In boys the mean increase in lengths of trunk amounted to 17.7 cm, of hand to 8.1 cm, of forearm to 12.2 cm, of upper arm to 16.1 cm, of whole arm to 36.8 cm of lower leg to 21.5 cm, of thigh to 27.3 cm, and of whole leg to 54.0 cm. The corresponding lengths in girls amounted in 16.9 cm, 7.2 cm, 11.0 cm, 14.0 cm, 32.6 cm, 18.7 cm, 24.5 cm, and 46.4 cm. Lengths investigated increase almost linearly between 3 and 11 years of age both in boys and girls. Beginning with 12 years boys have an increased development of all lengths when compared with girls.

Adolescent↗
PubMed1980

[Longitudinal data of blood pressure and pulse frequency during childhood (author's transl)].

From 1968-1980 the development of blood pressure and pulse frequency in 221 healthy boys and 230 healthy girls aged 2-16 years was studied longitudinally. An automatic blood pressure device recording on a paper tape pulse frequence as well was used. Systolic readings are taken at the first appearance, diastolic readings at the disappearance of the Korotkoff sounds. A steady increase of the systolic, and to a lesser extent, of the diastolic pressure can be observed. Boys have a more pronouned increase of systolic pressure than girls. From year 2-16 the 50th percentile increases from 90 mm Hg to 128 mm Hg in boys and from 92 mmHg to 116 mm Hg in girls. The 50th percentile of diastolic pressure increases from 61 to 66 mm Hg in boys and 65 to 71 mm Hg in girls. Pulse frequency of boys is comparable to that of girls. The 50th percentile decreases from 100 to 75 beats. Increasing age is paralleled by decreasing pulse frequency.

Adolescent↗
PubMed1992

Fitting growth curve models to longitudinal data with missing observations.

We discuss the analysis of growth curve data with missing or incomplete information. The approach is to fit subject-specific models and then to carry out an analysis in terms of the estimated parameters. This achieves reduction of data and eliminates the need for special considerations for subjects with missing data. Although there is no perfect substitute for complete data, our approach provides a way to handle missing data using a straightforward application of well-known statistical methodology.

Cephalometry↗
PubMed1997

Using word recognition tests to estimate premorbid IQ in early dementia: longitudinal data.

This study examined the utility of word recognition scores for estimating actual Verbal IQ scores obtained from 1-5 years earlier. Participants were 271 persons remaining normal and 24 initially normal persons who developed cognitive impairment over longitudinal follow-up. A previously published regression equation based on education and the American modification of the National Adult Reading Test (Nelson, 1982) was used to estimate Mayo Verbal IQ. In spite of correlating well with prior obtained scores (r = .7) the predicted score tended to overestimate the obtained Mayo Verbal IQ. A revised equation was developed in the normal sample, which improved accuracy of prediction. Among the 24 persons who developed cognitive impairment over a 5-year span, the revised predicted scores provided reasonable estimates of initial Mayo Verbal IQ. To aid in clinical interpretation, a table of the normal frequencies of predicted Mayo Verbal IQ minus contemporaneously obtained Mayo Verbal IQ is provided.

Aged↗
PubMed2005

Simultaneous modelling of survival and longitudinal data with an application to repeated quality of life measures.

In biomedical studies, interest often focuses on the relationship between patient's characteristics or some risk factors and both quality of life and survival time of subjects under study. In this paper, we propose a simultaneous modelling of both quality of life and survival time using the observed covariates. Moreover, random effects are introduced into the simultaneous models to account for dependence between quality of life and survival time due to unobserved factors. EM algorithms are used to derive the point estimates for the parameters in the proposed model and profile likelihood function is used to estimate their variances. The asymptotic properties are established for our proposed estimators. Finally, simulation studies are conducted to examine the finite-sample properties of the proposed estimators and a liver transplantation data set is analyzed to illustrate our approaches.

Algorithms↗
PubMed2004

Increased risk of head tremor in women with essential tremor: longitudinal data from the Rochester Epidemiology Project.

In one cross-sectional study of a community in northern Manhattan, women with essential tremor (ET) were more likely to have head tremor than were men. In that study, patients were seen at one point in time, rather than followed longitudinally. Head tremor often develops after arm tremor, and its appearance in patients with ET may therefore be a function of duration of follow-up. In a second epidemiological study utilizing the Rochester Epidemiology Project, in which ET subjects were followed from disease diagnosis to death, we determined whether there was an association between female gender and head tremor. We utilized the records-linkage system of the Rochester Epidemiology Project to identify ET cases. Records were reviewed and clinical data abstracted by a neurologist specializing in movement disorders. A second neurologist reviewed a subsample of records. There were 107 ET cases (69 women, 38 men) followed for 10.1 +/- 9.1 years from ET diagnosis to death. Head tremor was present in 37 (53.6%) women and 5 (13.2%) men (odds ratio [OR] = 7.6, 95% confidence interval [CI] = 2.7-21.9, P < 0.001). In a multivariate linear regression analysis, women remained at high risk for head tremor (OR = 6.5, 95% CI = 2.2-19.0, P = 0.001) independent of disease duration. We found in this longitudinal epidemiological study that women with ET were six times more likely to develop head tremor over the course of their illness than were men. The reason for the association between gender and head tremor, which has now been demonstrated in several studies, is not known, but it could reflect gender differences in the distribution of disease pathology within the brain.

Aged↗
PubMed2003

An autosome-wide search using longitudinal data for loci linked to type 2 diabetes progression.

A genome-wide screen was conducted for type 2 diabetes progression genes using measures of elevated fasting glucose levels as quantitative traits from the offspring enrolled in the Framingham Heart Study. We analyzed young (20-34 years) and old (>or= 35 years) subjects separately, using single-point and multipoint sibpair analysis, because of the possible differential impact of progression on the groups of interest. We observed significant linkage with change in fasting glucose levels on 1q25-32 (p = 5.21 x 10(-8)), 3p26.3-21.31 (p = 1 x 10(-11)), 8q23.1-24.13 (p = 2.94 x 10(-6)), 9p24.1-21.3 (p = 7 x 10(-7)), and 18p11.31-q22.1 (p < 10(-11)). The evidence for linkage on chromosomes 8 and 18 was consistent for the subset of study participants aged 43 through 55 years.

Adult↗
PubMed2005

Hearing levels of firefighters: risk of occupational noise-induced hearing loss assessed by cross-sectional and longitudinal data.

OBJECTIVE: It is well known that firefighters face serious risk to their health and safety in the performance of their duties. To determine whether individuals who work as firefighters sustain occupational noise-induced hearing losses, we evaluated results of hearing tests completed by firefighters and compared them with age-matched, non-occupationally exposed groups of individuals. DESIGN: The results of annual audiometric testing and a related questionnaire collected as part of a company-wide hearing conservation program were obtained from two large urban fire departments. The records from 12,609 tests conducted over an 11-year period were evaluated. Hearing levels obtained from the tests were compared with age-matched control populations from an American national standard, and a longitudinal study comparing the rate of hearing loss to that expected due to presbycusis alone was conducted. RESULTS: Comparisons of the data to the national standard indicated that firefighters do not exhibit excessive loss of hearing compared with age-matched, non-occupationally exposed control subjects. The longitudinal study that examined the regression of firefighters' hearing with age compared with the expected presbycasic regression function indicated that the hearing of firefighters in the study declined over the 7-year period at a rate that was less than that expected due to age alone. CONCLUSIONS: The results of this large-scale, cross-sectional, and longitudinal study indicate that firefighters are not at risk for occupational noise-induced hearing loss, even though they work nonstandard shifts and are occasionally exposed to high levels of noise. The results are consistent with the findings but not the conclusions of several other studies of firefighters' hearing.

Adult↗