# Questions tagged [growth-model]

A growth model is a statistical model describing the growth of some population, be it in demographics, biology or otherwise. A well-known example is the logistic growth model.

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### Variance-covariance structure for random-effects in lme4 or nlme (covariance specification)

I am running a multilevel growth model with multiple random slopes. In the Mplus software, I can specify exactly which random effect covariances are estimated (and which are not). For example, I can ...
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### Growth rate: how to avoid division by zero

I'm calculating the growth rate in productivity of some workers after an event. I have the output of the workers after the event, let's call it b, and the output ...
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### Lagged predictors in irregular-time / asynchronous / time-unconstrained data

In growth curve modeling or other approaches, when time is constrained/synchronous/regular (i.e. panel/wave data; all observations occur synchronously), lagged prediction is trivial - simply add t-1 ...
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### Latent Growth Modeling in Lavaan

Lavaan newbie here. I've been trying to specify a latent growth curve model in R for a few days now and been going through all the tutorials on the Lavaan website. The theoretical path is reasonably ...
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### What transformations are permitted before a t-test for significance?

I have been using t-tests to test for significant differences between the means of populations. Specifically, I am trying to determine if revenues have increased significantly before and after a ...
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### Using change in one variable (2 timepoints) to predict change in another variable (2 timepoints): latent change models?

I have two variables, both measured at two timepoints: before and after an experimental procedure. I'm expecting that change in one variable from Time 1 to Time 2 will predict change in the other ...
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### Highly correlated linear and quadratic slope in Growth model; cov matrix not definite positive

I'm running a a Growth model in R using the package lavaan, function growth.mi(), on an imputed dataset with four measurement points. The model estimates an intercept, a linear slope, and a quadratic ...
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### Latent growth curve model in lavaan: "WARNING The smallest eigenvalue of the EM estimated variance-covariance matrix (Sigma)..."

When running a latent growth curve model in lavaan (see code below) I get the following warning message: ...
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### Examining growth rates and sex differences

I'm trying to figure out the best statistical test to use to understand my data. I've searched but haven't found anything super applicable. I'm working with an endangered animal species and have a lot ...
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### Trying to fit a Latent Growth Model in R and I get the error " Could not compute standard errors! The information matrix could not be inverted."

I know that there are several other posts dealing with this same issue but I still can't seem to figure out why my model isn't working. I don't believe it is under identified because it is a fairly ...
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### How to calculate exponential growth when the value is a percentage or probability?

I have a variable x that takes values between 1 and 0 (0<x<1). I want to calculate value of ...
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### SEM warning message "WARNING: some estimated lv variances are negative" (Latent growth curve model)

When running a quadratic latent growth curve model (model_6 below) I get the following warning message: "...
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### Vanishing partial derivative of least squares w.r.t. Verhulst growth parameter

The Verhulst growth model can be given as $$P(t) = \frac{k}{1+ \left( \frac{k-P_0}{P_0} \right)\exp(-rt)}$$ where $P(t)$ is the population size at time $t$, $k$ is the carrying capacity, $P_0$ is the ...
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### Using the FSA R package to test effect of continuous covariates on von Bertalanffy growth rate

Is it possible to use the FSA package in R to test for the effect of continuous variables (such as temperature, latitude, precipitation). I have recapture growth data and am able to test for the ...
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### Can the same variable be used as the response variable twice in the same Bayesian model?

I am working on an individual growth model to predict snout-vent length (SVL) in snakes as a function of age. We have some individuals where we know their total length (TL = SVL + length of the tail) ...
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### Growth curve model with structured missingness

I am attempting to fit a growth curve to data relating to school-aged children, 11-16. The data is collected at each year, across 5 years. Some individuals will have complete data (all 5 time points), ...
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### How to compare replicated time series

I have several cell cultures at different salinities. I have 4 replicates at each salinity. You can get an example of the data, with 2 salinities, here: ...
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### Inclusion of random effects terms in growth curve analyses - Grouping variable and Group x Time interaction term

I am using growth curve analyses to test whether a 2-level between-person randomized intervention impacts patient anxiety trajectory. I am including Group, Time, and Group x Time as fixed effects, and ...
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### Analyzing the pattern in the growth of organisms using discrete data in R

I have data of the size of 200 individuals of a particular plant species. But the size was measured in an indirect way, counting the number of leaves (discrete data), monthly during a total of 14 ...
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### Random slopes in a growth curve analysis

I want to test whether an intervention affects a continuous outcome over 5 possible time points. How do I decide whether to include random slopes? I want slope to be able to vary between intervention ...
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### Finding max dichotomies of a matrix $B(N,K)$

Before I begin, this question is different from this question. Anyways, I was also reading Yaser Mostafa's book "Learning from Data" and came across this matrix: And in the book the author ...
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### Saturating growth model for binomal data

I need to estimate a probability from a set of successes observed over time. I this application I have multiple ‘looks’ at the data, and need to estimate ‘p’ from this. Because of this, i thought that ...
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### growth curve modeling for nominal and ordinal dependent variables

Is it possible to conduct growth curve modeling for nominal and ordinal dependent variables instead of a continuous variable? The aim is to investigate the nature of the growth trajectories and to ...
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### Estimating growth rate from noisy data?

Let's say we want to estimate growth rate from noisy data. Due to noise, simple calculation will result in very poor estimates (calculating growth rates just exacerbates noise), so smoothing is needed....
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### Multi-level Mixed-effect Modeling of Growth Trajectories: Grand mean-centering or Transformation to Normal for Dependent Variable?

When it comes with analyzing growth trajectories by multi-level mixed-effect modeling, What would be technically appropriate when the dependent variable originally shows a severe positive skewness ...
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### Laavan -Growth curve models with indirect effects

I have a latent growth model (growth curve model) with time-varying covariates. I also want to to test for the possibility of indirect effects through the tine varying covariate. Does Laavan allow for ...
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### How to run a nls for multiple dependent variables?

I am unfamiliar with nls however after doing some research on the function it seems to be appropriate for my current analysis. I am testing population declines over ...
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### Can I include individuals with a single data point in a growth curve model?

I read that one of the main advantages of using a growth curve model is that it can handle missing data. Some of the participants in my study have data for only one time point, while most have data ...
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### Orthogonal contrasts and the poly function in R: Interpreting the coefficients as "absolute" or "incremental" effects

in a growth curve like model, I try to test whether a trajectory (over time) is better described by a linear or quadratic trend. I fitted a linear mixed model (time nested in participants) and called ...
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### growth curve model (with age as a predictor) - unbalanced design

I have longitudinal data in which participants who were of varying age at baseline were followed up for ten years. There are many attritions so for some participants, I have data for when they were 20,...
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### Predict a variabile Y from X1 and X2 repeated measures

I have measured two times a variable X, having a T0 and a T1 measure of X in a sample of 60 individuals'. I would expect that growth of this parameter could predict a variable Y. In order to verify ...
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### Contribution to Growth for a linear equation

I have this equation $Sales = Impressions * CTR * CVR * Price$ I know all the values for two different periods (January 2021, February 2021) and I want to know how much each components (impressions, ...
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### growth function with higher tail growth

I am trying to fit a model to performance data by age. However the model I am getting predicts a much slower growth rate at high ages than the data would suggest (by looking at it). Is there a better ...
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### Many short groups - a growth model in lmer

I'm looking at a test score variable in a longitudinal study of around 10000 children, recorded over three waves (Ages 3,5 and 9). I have every reason to believe that there is substantial variation in ...
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### How to use Latent Growth Curve Modeling

I have data from a longitudinal study with variable X measured at 19 time points. In a follow-up questionnaire I have variable Y representing the results from a psychometric questionnaire. Now I want ...
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### R fit a logistic regression of the form $y=\frac{c}{1+ae^{-bx}}$ [duplicate]

I'm working through some textbook exercises on fitting models to data, including exponential, logarithmic and now logistic regression. About a 3rd of the way down this page is the section on logistic ...
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### Modeling exponential growth with mixed effects

I'd like to create an exponential growth/decay model along the lines of y ~ -a * exp(-b * x) in R. I have been able to do this using nls(), but my dataset has repeated measures, so I need a mixed ...
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### How do I structure my data in a time-lagged, multilevel mediation?

I am analyzing a repeated measures experiment using a multilevel growth curve in SPSS. I want to test a time-lagged, multilevel mediation model. My X variable is linear time in weeks (week 1, week 2, ...
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### Adjustment factor in logistic growth model of facebook-prophet

In the paper it emphasizes: "When the rate k is adjusted, the offset parameter m must also be adjusted to connect the endpoints of the segments. The correct adjustment at changepoint j is easily ...
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### Latent variable two time-point model

I have a latent variable that was measured at 2 time points, and I want to model the growth in this latent variable. I then want to examine how variations in slope and intercept differ by latent and ...
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### How do I control for baseline differences between groups in a multilevel growth curve?

I am analyzing a repeated measures experiment with 3 groups using a multilevel growth curve in SPSS. I have represented my 3 groups with 2 dummy variables (d1 & d2). I have discovered that there ...
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### How do I control for a level-2 time-invariant covariate in a multilevel growth curve?

I am analyzing a repeated measures experiment with a multilevel growth curve in SPSS. I want to control for a potential confound (baseline social support) when looking at differences in depressive ...
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### Which statistical test can I use for a set of abnormal data trend?

I am doing a biology experiment about the effects of 5 different concentrations (0%,25%, 50%, 75%, and 100%) on plant growth. It was a 5×5 trial. From 0% to 50% my plant's height increased, with 50% ...
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### Adding level 1 time-varying predictor makes mixed effects model non-linear

I am new to mixed effects modelling and I am trying to predict depression from physical activity using mixed effects modelling / multi-level modelling. The data consists of timepoints in months (7 ...
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### What is the mean average of $y=kg^t$ from $t=a$ to $t=b$ [closed]

Mean average of $y$ in $y=kg^t$ from $t=a$ to $t=b$. $g$ is a constant, $t$ varies. I have looked this up in textbooks and online and all I can find is the mean average of a function where $t$ is a ...
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### Interpreting growth curve analysis (GCA) main effect in light of interaction (eye tracking data)

I have fit parabolas to two groups in a growth curve analysis (GCA) of eye tracking data using orthogonal polynomials (essentially by following Dan Mirman's example for his paper with Magnuson in 2009,...
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### Confidence Intervals for the Parameters of a Logistic Growth Curve

I'm using the growthcurver library to estimate the parameters from some bacterial growth curves. It fits a logistic equation of the following form: This returns ...
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### Statistical inference for morphogenesis models

I work developing morphogenetic models of plant tissues. In short, a typical model of this kind would be a single starting cell that grows and divide, while exchanging molecules with other cell based ...
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