# 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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### Strange increase in residual variance after adding TVC

I have three growth curves models. Model 1 with just fixed control variables. in a separate model I add a dichotomous, time-varying categorical variable which actually increases the residual variance- ...
25 views

### 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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### How to generate data with prespecified autocorrelation and random crosscorrelation in a growth model?

I would like to simulate data from an unconditional growth model with one fixed (level 2) covariate $x_{i}$, cross-correlation $\rho_c$ and autocorrelation $\rho_a$. The model should have a random ...
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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% ...
26 views

### 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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### Get initial parameters for growth models with nls whith non-common functions like “Ricker2” or “Richards” functions

I usually fit the most commonly known growth models using the FSA library and with the function selfStart. Now, I am trying to test some models with the Original Gompretz vbFuns("Ricker2") ...
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### Quadratic growth with only three time points (latent growth curve modeling)

I am trying to model change in, let's say in "depression" [DEP], across three time points (T1-T2-T3). Using Latent Growth Curve Modeling I succeeded to fit a linear model (i.e., intercept ...
62 views

### 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,...
50 views

### Comparing lmer and LCMM (single class) models

I am modeling the same dataset using both lmer and LCMM. My understanding is that if I use class count of 1 for LCMM, the models derived from both methods should be very similar. However, as seen in ...
69 views

### 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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### Residual variances contrained to zero in LGCM

I am trying to fit a quadratic term with three time points. Given the number of parameter/df issue, is it ok or meaningful to set the residual variances of the observed variables to zero (just to ...
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### How to calculate average growth and average growth rate. Use the results to predict the figure for the next two years in line?

I'm trying to do what I described in the title of this question. I got the following table which I filled, but I'm not pretty sure how to "predict" what's going to happen in the next two years. For ...
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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 ...
23 views

### Measuring “consistent” growth versus “spiked” growth

I have a time-series database of users and their growth on our platform over time. I am trying to determine from this database users who are showing a consistent growth over time (and especially ...
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### lme4 non-linear modelling with missing values

I am using lme4 R package for modelling growth curves (ref: Mirman, Daniel, 2017). The code below shows an example suggested in the book about modelling non-linear growth curve (GC) models, the data ...