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- ...
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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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34 views

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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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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16 views

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 ...
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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,...
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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 ...
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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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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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9 views

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 ...
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1answer
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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1answer
89 views

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 ...
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59 views

Should I interpolate missing data, or is the last-known value good enough?

I want to study the yearly weight change of a population of about 100 people. I have about 100k measure taken at random intervals over a 10 year period. Each samples point is represented as a 3uple: $...
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How to plot charts symmetrically around 1, like geometrical growth multipliers?

Geometrical growth could be represented as a series of multipliers $V_i = V_0 \prod d_i$. The series will be centred around 1 and when plotted upper side would look larger. When in reality the ...
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Using sample means and standard deviations to recreate a Von Bertalanffy Growth Model with CI or PIs

Bit of a complex problem here and I'm not sure if this is quite the proper location, but was my best guess. Hopefully someone here will have some concept of what I'm attempting. For a 10 year study, ...
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35 views

Study the impact of an external force on the behavior of a system over time

(I am not a statistician, so please pardon my naive stats language.) Consider an event that has started at time t_i and is running till present; the event is ...
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How to test for significant differences between growth curves in repeated measures mixed-models?

I am comparing growth of fish in different habitats and since length and age data is derived from repeated measurements (back-calculations) I am using a mixed model (R, nlme). I have data from ~50 ...
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is LGM without factor variance just comparing means?

Let’s say a simple latent growth model with just two time points, constrained the variance of these two time points to be zero. Are the latent intercept and latent slope then merely using the mean ...
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29 views

Nonparametric equivalent of mixed model for nested data?

I have collected a nested data measuring cell growth which has two levels (3 patients with disease A, another 3 patients with disease B, another 3 patients with disease C). For each patient, cell ...
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ML method to determine growth of accounts in a bank

Assume a bank has today N checking accounts, and also has 10 years history of the account balances. The history also includes related features such as "Allow overdraft" (Yes/No) and "Opening branch" (...
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46 views

Estimating common slope across two traits for a parallel growth curve model

I am using a parallel growth curve model with 5 waves longitudinal data to evaluate correlated change among 2 traits. For models that showed the effects of correlated change among traits, I'm ...
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202 views

Modeling growth curves with different starting sizes (NLME in R)

I am trying to model fish egg growth over time given a starting egg size in R. I have repeated-measures data from individuals with grouping variable "Zafra.1". I do not know when the eggs started ...
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1answer
94 views

Interpreting the latent growth model output

I started to go through this interesting structural equation model called latent growth curve model. When i go through some research articles that involved latent growth curve models, I found this ...
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1answer
525 views

How to calculate growth rate from a semi-log plot?

In the following plot, if we model the population growth as a linear function of time, what would be a good estimate of the linear growth rate? I don't know if it's the slope or the intercept!
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61 views

How do you choose an appropriate time series regression model?

I am working on a research proposal where I want to test the effect of different macroeconomic variables (i.e. government spending, FDI, trade openness, international GDP growth, etc.) on the GDP ...
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80 views

Dealing with different units and indexes in regressions

In my time series model, my dependent variable is a growth measure in percentage. However, one of my independent variables is an index that ranges from -2.5 to 2.5 - and is producing some extreme ...
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Change in X Predicts Change in Y

I have a fairly small sample (about 50 individuals) measured at three points in time. At each time point, I measure an outcome (Y) and a possible influence on that outcome (X) along with some ...
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72 views

Path analysis of latent variable relationships over time for hypothesis testing

Consider that I have a sample of 30 people (my real data are much bigger), and we ask them how often the would like to eat three types of food (candy, vegetables, and meat) at four points in their ...
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How to compare growth rates estimated from GLMM?

I've counted aphid populations under 5 different treatments for about 10 weeks. There were 4 replicates of every treatment. I'm interested in comparing the first 4-5 weeks, where the populations ...
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31 views

What test to use to compare within-group over time?

I have a set of data of $\approx 13$ people. We collect their data every 2 months for 2 years. I'm interested to see if a variable A in the data affect people's performance as well as their growth ...
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221 views

Fitting a logistic growth curve with an iterative formula in R [closed]

I'm trying to fit a logistic growth curve to specific countries GDP data using an equation, $P_{n+1} = rP_n(1-\frac {P_n}{k})$. (1) I've found constants $r$ and $k$ simply by finding a ...
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103 views

Latent growth curve model with more time points than participants

I can't quite figure out if having more time points in a latent growth curve model reduces power or increases it. I don't have the data yet so I can't experiment. The study has around 300 measurement ...
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152 views

How to specify LMER model to customize different predictors on random intercepts and slopes

I'm trying to specify a longitudinal growth curve model (mathematically defined in Bollen & Curran's 2006 Latent Curve Model book, Chapter 6). Here's some brief theoretical context for this ...
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1answer
60 views

What statistical model to use for assessing the effect of a new tree pesticide?

I have 2 sites with 15 trees on each site. I plan to treat all 15 trees in site 1 with a new pesticide and leave all 15 trees in site 2 untreated. The total number of bugs on each tree is measured ...
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104 views

Modeling a repeated measures growth curve

I have cumulative population totals data for the end of each month for two years (2016, 2017). I would like to combine these two years and treat each months cumulative total as a repeated measure (one ...
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Are there extensions of the latent-class growth model where also the outcome is unobserved?

In my understanding, in a repeated-measure setting, Latent-Class Growth Models (LCGM's) use latent factor to represent growth parameters. In my case, I have repeated measures where also the outcomes (...
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1answer
156 views

Interpreting fixed effect time and cross-level interaction time in growth model (multilevel model)

In my dataset time is nested within person. I have done a multilevel analysis with time on the first level and subject on the second level. There is a significant fixed effect of time on the dependent ...
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337 views

Growth Curve Models using lmer() function in R (lme4 package)

I am interested in changes in depression surrounding different life events and if personality traits (level-2 predictors) affect these changes in depression. In a given longitudinal data set, each ...
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871 views

asym, xmid, scal biological interpretation for Self-Starting Nls Logistic Model

I built logistic models using self-starting nls logistic models using SSlogis and nls functions in the base 'stats' package in R. I had a couple questions about the biological interpretation of the ...
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How to report Likelihood Ratio as Chi2 / Δχ2 value

I'm comparing different models of a growth model using RStudio and the anova(model1, model2) command. I get an output like (values completely random, just as example): ...
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Mixed Effects model with quadratic term in fixed, but not in random part

Say one wishes - and believes - to fit a mixed effects model where time ($x_{ij}$ below) is included in a linear and quadratic term in the fixed part, but only linear in the random part (hence random ...
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Students nested in both middle and high schools over time - what to do?

I have a question about one of the papers I'm reviewing. The authors used a piecewise growth curve model to estimate trajectories of key variables before and after the middle to high school transition....
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1answer
1k views

Baseline adjustment in growth models: Random Intercept or Baseline Covariate

Let's say I have outcome data at four time-points (baseline, 3 months, 6 months, 12 months) which I want to regress on an explicit time variable ($t_1 = 0$, $t_2 = 1$, $t_3 = 2$, $t_4 = 3$) to ...
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1answer
1k views

How to compute number of dichotomies/growth function value?

I am studying the book 'learning from data' by Mostafa. I understand that the number of dichotomies for positive rays on the number line is $N+1$ (ie if you have one point, $x$, on the number line, ...
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Growth Mixture Models in MPlus

I'm new to mixture modeling and MPLUS, so apologies if this question is misguided. I am currently working through a dataset and learning off of Higher-Order Growth Curves and Mixture Modeling with ...