Generalized latent class modeling using gllamm

gllamm can estimate both conventional and unconventional latent class models. Models are specified using discrete latent variables whose values determine the conditional response distributions for the classes. A new feature of gllamm is that latent class probabilities can depend on covariates. We will first discuss the conventional exploratory latent class model. When a number of fallible diagnoses of some disease are available, this model can be used to estimate the prevalence of the disease as well as the sensitivities and specificities of the tests in the absence of a gold standard. After estimating the model in gllamm, gllapred can be used to diagnose individual subjects based on their posterior class probabilities. An advantage of using gllamm is that a wide range of response types can be accommodated. To illustrate this, we consider the analysis of rankings of political goals in the study of value orientations. We will also discuss confirmatory models such as latent class factor models and apply them to attitudes to abortion data, taking the survey design into account by using probability weighting and robust standard errors. Finally, we consider latent trajectory models for investigating distinct patterns of change in longitudinal data.

Intervention evaluation using gllamm

The gllamm procedure provides a framework in which to undertake many of the more difficult analyses required for trials and intervention studies. Treatment effect estimation in the presence of noncompliance can be undertaken using instrumental variable (IV) methods. I illustrate how gllamm can be used for IV estimation for the full range of types of treatment and outcome measures and describe how missing data may be tackled on an assumption of latent ignorability. I will describe other approaches to account for clustering and the analysis of cluster-randomized studies. Examples from studies of alcohol consumption of primary-care patients, cognitive behavior therapy of depression patients, and a school based smoking intervention are discussed.

Do historical changes in parent-child relationships explain increases in youth conduct problems?

The coincidence of historical trends in youth antisocial behavior and change in family demographics has led to speculation of a causal link, possibly mediated by declining quality of parenting and parent-child relationships. No study to date has directly assessed whether and how parenting and parent-child relationships have changed. Two national samples of English adolescents aged 16-17 years in 1986 (N = 4,524 adolescents, 7,120 parents) and 2006 (N = 716 adolescents, 734 parents) were compared using identical questionnaire assessments. Youth-reported parental monitoring, expectations, and parent-child quality time increased between 1986 and 2006. Ratings of parental interest did not change. Parenting differences between affluent and disadvantaged families narrowed over time. There was thus little evidence of a decline in quality of parenting for the population as a whole or for disadvantaged subgroups. Parent-reported youth conduct problems showed a modest increase between 1986 and 2006. Findings suggested that the increase in youth conduct problems was largely unrelated to observed change in parent-child relationships

Prenatal anxiety, maternal stroking in infancy, and symptoms of emotional and behavioral disorders at 3.5 years

Animal findings of long-term effects of maternal behaviors mediated via altered GR gene expression will, if translated into humans, have far reaching implications for our understanding of child and adolescent psychopathology. We have previously shown that mothers’ self-reported stroking of their infants modifies associations between prenatal depression and anxiety and child outcomes at 29 weeks and 2.5 years. Here, we examine whether the effect of early maternal stroking is evident at 3.5 years, and in a much larger sample than in previous publications. A general population sample of 1233 first-time mothers completed anxiety measures at 20 weeks gestation, 865 reported on infant stroking at 9 weeks, and 813 on child symptoms at 3.5 years. Maternal stroking moderated the association between pregnancy-specific anxiety and internalizing (p = 0.010) and externalizing (p = 0.004) scores, such that an effect of PSA to increase symptoms was markedly reduced for mothers who reported high levels of stroking. There was no effect of maternal stroking on general anxiety. The findings confirm the previously reported effect of maternal stroking, and in a much larger sample. They indicate that there are long-term effects of early maternal stroking, modifying associations between prenatal anxiety and child emotional and behavioral symptoms

Applications of -gllamm- in health evaluation studies

-gllamm- provides a framework within which many of the more difficult analyses required for trials and intervention studies may be undertaken. Treatment effect estimation in the presence of non-compliance can be undertaken using instrumental variable (IV) methods. We illustrate how -gllamm- can be used for IV estimation for the full range of types of treatment and outcome measures and describe how missing data may be tackled on an assumption of latent ignorability. Alternative approaches to account for clustering and analyse cluster-randomised studies will also be described. Quality of life and economic evaluation of outcomes often makes use of discrete choice and stated preference experiments in which illness scenarios are assessed. We illustrate how -gllamm- can be used for the analysis of data from such studies, whether these are in the common form of paired comparisons or the more complex case where multiple scenarios are ranked. Examples from studies of a school-based smoking intervention, a re-employment encouragement experiment, a group therapy trial and of quality-of-life with rheumatoid arthritis will be considered.

Maternal mental health and child problem behaviours: disentangling the role of depression and borderline personality dysfunction

Background It is not known whether associations between child problem behaviours and maternal depression can be accounted for by comorbid borderline personality disorder (BPD) dysfunction. Aim To examine the contributions of maternal depression and BPD symptoms to child problem behaviours. Method Depression trajectories over the first-year postpartum were generated using repeated measurement from a general population sample of 997 mothers recruited in pregnancy. In a stratified subsample of 251, maternal depression and BPD symptoms were examined as predictors of child problem behaviours at 2.5 years. Results Child problem behaviours were predicted by a high maternal depression trajectory prior to the inclusion of BPD symptoms. This association was no longer significant after the introduction of BPD symptoms. Conclusions Risks for child problem behaviours currently attributed to maternal depression may arise from more persistent and pervasive difficulties found in borderline personality dysfunction

Differential population synthesis of 17 early-type galaxy nuclei in the Fornax cluster

Flux calibrated spectra have been obtained of the nuclei of 12 Elliptical and 5 Lenticular galaxies in the FORNAX cluster, at a resolution of 10 - 20 A and in the wavelength range 0.36 to 0.72 micron. The observations have been extended to a long wavelength limit of 0.88 or 1.0 micron for 12 of the galaxies. The galaxies observed cover a 6 magnitude range of absolute magnitude and define the form and intrinsic width of the cluster colour-magnitude relation well. The galaxy spectra have been synthesised with a flux library of 48 synthesis standard spectra, compiled from spectrophotometry of ~200 stars in the wavelength range 0.36 to 1.0 micron at a resolution of 15 A. The stars observed cover a complete solar abundance sequence of all spectral types and luminosity classes, with additional metal-weak and metal-rich G-K giant branch sequences. The results presented here confirm that population synthesis of several galaxies covering a large range of absolute magnitude in one cluster permits good differential comparison of the mean galactic metallicities and ages associated with the main sequence turnoff group. The major conclusions are : 1) The metallicity results confirm the well known trend of decreasing mean metallicity with decreasing galactic luminosity. A metallicity gradient in [Fe/H] of at least 0.16 dex per magnitude is indicated over the 6 magnitude range of absolute magnitudes studied here. The brightest ellipticals NGC1399 and NGC1404 are 2 to 3 times more metal-rich than solar. The trend of mean metallicity with luminosity is the principle factor determining the slope of the cluster CM relation. 2) The ages associated with the main sequence turnoff groups are generally quite young (6 to 10 Gyr). This implies that substantial star formation has occurred in all early-type galaxies for about 8-10 Gyr after the epoch of globular cluster formation. The only possible trend of turnoff age with luminosity is towards younger ages (more extended star formation) in brighter ellipticals. 3) The turnoff ages of the lenticulars are significantly older (> 3 Gyr) than those of ellipticals of the same absolute magnitude, implying that star formation terminated earlier in lenticular systems. The mean metallicity of the lenticulars is also lower than that of ellipticals of the same absolute magnitude. 4) Three bright ellipticals (NGC’s 1404, 1399 and 1379) show strong evidence for a significant blue light contribution due to late 0 dwarfs, implying some ongoing star formation in at least these systems. Syntheses of other early-type galaxies also favour some 0-B dwarf contribution, but these galaxies can be equally well fitted with an enhanced metal-weak G-K giant contribution and some horizontal branch starlight. A significant 0 dwarf contribution (10 % at U) is consistent with a strong turnup in the uv flux below 1800 A, whereas a purely horizontal branch contribution would provide a ~flat uv continuum. Hot dying stars can not be present in sufficient numbers to contribute significantly to the uv flux in any early-type galaxy. UV bright stars could provide a significant fraction of the uv flux in the fainter, metal-weak galaxies. 5) There is a weak correlation between the percentage light contribution due to OB dwarf stellar groups, and the colour residuals from the mean (U36-V) vs. V nuclear colour-magnitude relation. Variations in the contribution due to recently formed OB dwarfs could account for a significant fraction of the intrinsic width in (U-V) of the cluster CM relation. 6) The faintest ellipticals studied here have absolute magnitudes similar to that of M32. The faintest elliptical 0333-36 is isolated from other galaxies and is clearly very metal-weak with [Fe/H] < -0.6. Star formation ceased at least 8 Gyr ago in 0333-36. The faint elliptical JJ79 is situated in the cluster core close to several other early-type galaxies. The metallicity of JJ79 is solar or greater, and this galaxy shows strong indications that substantial star formation activity occurred as recently as 3 Gyr ago. Relatively high (solar) metallicity and indications of recent star formation in low luminosity ellipticals such as M32 and JJ79 are probably consequences of tidal interactions with massive companions. The population synthesis technique can also give galactic mass to light ratios which are independent of distance. The results show that detailed population syntheses of near infra-red spectra from 0.7 to 1.0 micron enable only upper limits to be reliably calculated for the mass to light ratios of early-type galaxies. The conclusions regarding galactic mass to light ratios are : 7) The measured near infra-red spectra of galaxies can be well fitted by several combinations of M dwarf to M giant contribution ratios, resulting in M/Lv ratios in the range 1 to 13 for most early-type galaxies. The Na I doublet feature at 8190 A does not provide sufficient discrimination between M dwarfs and M giants to determine more precise values of M/Lv, although the fairly low measured equivalent widths clearly excludes M/Lv values greater than 20. Good quality spectra of the Wing-Ford (FeH) band at 9910 A may enable more reliable estimates of mass to light ratios to be derived from synthesis techniques. 8) Upper limits to M/Lv ratios calculated from synthesis fits conform well with M/Lv ratios calculated from nuclear velocity dispersion measurements. There is no reliable evidence for hidden mass in the nuclei of early-type galaxies of any luminosity. The dynamical estimates are consistent with galaxy M/L^ values of about 5 (M/LB ~ 7) , independent of absolute magnitude

How does perinatal maternal mental health explain early social inequalities in child behavioural and emotional problems? Findings from the Wirral Child Health and Development Study

This study aimed to assess how maternal mental health mediates the association between childhood socio-economic conditions at birth and subsequent child behavioural and emotional problem scores. Analysis of the Wirral Child Health and Development Study (WCHADS), a prospective epidemiological longitudinal study of the early origins of child mental health (n = 664). Household income at 20-weeks gestation, a measure of socio-economic conditions (SECs) in pregnancy, was the main exposure. The outcome measure was externalising and internalising problems, as measured by the Child Behaviour Checklist at 5 years. We assessed the association of household income with child behavioural outcomes in sequential linear models adjusting for maternal mental health in the pre- and post- natal period. Children of mothers in more disadvantaged households had higher scores for externalising behaviour with a difference of 3.6 points comparing the most affluent to the most disadvantaged families (the socio-economic (SEC) gap). In our regression model adjusting for baseline confounders, comparing children of mothers in the most disadvantaged households to the least disadvantaged, we found that most disadvantaged children scored 45 percentage points (95% CI 9, 93) higher for externalising problems, and 42% of this difference was explained in the fully adjusted model. Adjusting for prenatal maternal depressive symptomology attenuated the SEC gap in externalising problems by about a third, rendering the association non-significant, whilst adjusting for pre- and post-natal maternal mental health attenuated the SEC gap by 42%. There was no significant relationship between household income and internalising problems. Social disadvantage is associated with higher child externalising behaviour problems score at age 5, and about 40% of this was explained by maternal perinatal mental health. Policies supporting maternal mental health in pregnancy are important to address the early emergence of inequalities in child mental health