# longitudinal study

1. ### Causation, correlational analysis and prospective studies

I am writing a systematic review of prospective studies, where two studies with two measurement points say that they cannot infer causation because of their correlational analysis. One report covariate analysis and path model, the other multiple regression analysis. But they don't explain why...
2. ### Restricted Maximum Likelihood (REML) Estimate of Variance Component.

Let, \mathbf y_i = \mathbf X_i\mathbf\beta + \mathbf Z_i\mathbf b_i+ \mathbf\epsilon_i, where \mathbf y_i\sim N(\mathbf X_i\mathbf\beta, \Sigma_i=\sigma^2\mathbf I_{n_i}+\mathbf Z_i \mathbf G\mathbf Z_i'), \mathbf b_i\sim N(\mathbf 0, \mathbf G), \mathbf\epsilon_i\sim N(\mathbf 0...
3. ### Defining Contrast Matrix

In the book Applied Longitudinal Analysis, 2nd Edition there is an example in the chapter "Marginal Models: Generalized Estimating Equations (GEE)" in "Muscatine Coronary Risk Factor Study" sub-section. I am illustrating it below : Let Y_{ij}=1if the i^{\text{th}} child is classified as obese...
4. ### Difficulty in Selecting Thesis Topic

I am a graduate student. I have a 6 credit thesis and I am interested in the field of longitudinal and Bayesian. My supervisor said me to choose my topic. But I am not understanding if I choose a topic how can I know what is the scope (further extension) of this topic because I can't only...
5. ### Multivariate Analysis for a paired subject longitudinal microbiome study

I am trying to finish my stats analyses for a microbiome study, and the last thing on my list is multivariate analysis. I have a paired group of infants and their primary caregivers with samples taken 5 times over a 1 year period along with clinical data (sex, feeding, delivery etc). I'm looking...
6. ### SAS GLIMMIX subject specific estimates

I am trying to analyze a dataset where each subject has 12 repeated measures (quarterly, over 3 years). I want to extract subject specific estimates of the time slope to evaluate if the subjects are changing significantly over time. The code I currently have consistently suggests that each...
7. ### Analysis of a longitudinal study where interventions are received at different times

I have a data set of university students. The university has 8 different assisting programs, mostly like scholarships, for needy students to help them concentrate on their studies. Since it costs a lot of money for the university to run these programs, it opts to evaluate how effective each of...
8. ### Longitudinal Adhesion Test for Patches

Hello dear colleagues. I have to compare the adhesion of two drugs in the form of transdermal patches. According to EMA's (European Medicines Agency) guidelines, the adhesion should be measured several times for each treatment, during the 24 hour period of administration of the drug, using...
9. ### longitudinal analysis help

Hi there Im struggling to figure out which statistical test i need to use on my data and then also how to carry this out in R or SPSS.... I have a time-series of measurements of pollutant levels on leaves from 4 different plant species that were re-sampled twelve times over a period of 5...
10. ### Interpreting main effects in long. mixed model when interactions w/ time are in model

I am running a mixed effects longitudinal model with linear and quadratic time effects and a continuous outcome. I have a covariate that has a significant interaction with time-squared, so obviously the linear interaction and its main effect are left in the model. When interactions are in the...
11. ### longitudinal mixed model troubles

I have growth data for 5 time points. In my unconditional model the quadratic trend best fits the data (likelihood ratio test). However, the random effect for the quadratic term is not significant but the fixed effect is significant. I also have trouble when adding covariates - the g matrix is...
12. ### Likert scale - questionnaire administered twice - longitudinal study

Hi, I am running a longitudinal study which lasted for few months during which all participants used a specific communicaiton device. I conducted a questionnaire at the beginning and the same questionnaire was administrated at the end of the study. All participants performed the same...