A statistical model is a formalization of relationships between variables in the form of mathematical equations. A statistical model describes how one or more random variables are related to one or more random variables. The model is statistical as the variables are not deterministically but ...
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11 views
Overdispersed Poisson fit data
I'm dealing with traffic volume count data. The Poisson is a good fit for the data when I determined using chi-square test but the dispersion index is slightly overdispersed.
How to deal with this?
...
1
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1answer
74 views
Making various mixed effects models
I've tried to create three models (using R): an intercept only linear regression, a simple mixed effects regression and a by-subject effects mixed effects regression.
An intercept only regression ...
0
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0answers
24 views
Nuisance Variable in Random Forest Model
I know I have significant annual variation due to observer bias in my data and also unequal sample sizes between years. I wanted to account for this by using "year" as a nuisance variable in a random ...
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0answers
17 views
How to perform model based feature classification
I am new to statistical modelling and so please pardon if the question appears trivial.
I have a set of multi-dimensional data ($T$) where each dimension represents features ($f_i$) obtained from ...
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1answer
33 views
How to model a multi-dimensional feature set for classification
I am new to statistical modelling and so please pardon if the question appears trivial.
I have a set of multi-dimensional data ($T$) where each dimension represents features ($f_i$) obtained from a ...
0
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1answer
37 views
Reduced models after finding significant interactions
If you run an ANOVA and find that there are significant interactions, do you then pull the variables out individually and re-run the ANOVA?
I am using Type III. I want to see if there is a ...
3
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2answers
95 views
+200
Population model to model year to year dynamics
My task is to assess how various environmental variables affect annual population fluctuations. For this, I would use a model like:
$$
\mbox{log} ( \mu_{i,j+1} ) = \mbox{log} ( \mu_{i,j} ) + R_{j} + ...
0
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1answer
42 views
Comparing models
Suppose that I have two models, A and B (A nested in B), which are tailored to explain data from a single participant in an experiment. Example: I am modeling response times in a single participant. ...
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0answers
11 views
System Identification regarding to L1-norm (absolute operator)
I am doing some control and system identification work right now, and I really need some help with respect to the system identification part.
Basically, I have a discrete state-space model, such as
...
0
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0answers
42 views
How to prove that selected sample is representative of the whole population?
I would like to prove that my approach towards selection of the sample set was correctly designed. I have a population of certain size. Out of this population I have selected a subset of diverse ...
0
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1answer
37 views
Multinomial logit model
Why do we need to use a base category (normalised to zero) when working with multinomial logit models?
I would also like to ask why do we need to report conditional logit coefficients?
Wouldn't ...
0
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0answers
39 views
Mean squared error — internal and external validation
This is probably a very easy question... but I am not quite sure what the right answer should be..
I have validated 3 beforehand selected models. I have done internal cross validation and I have ...
2
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0answers
23 views
Using non-significant data for modelling/predictions
Two medical interventions A and B were compared within randomised controlled trial:
differences in progression free survival (PFS, i.e. how long
patient lived with controlled disease, from ...
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1answer
33 views
Regression model F test and T test on different response variable?
I am comparing two different models (multiple linear model).
Basically the explanatory variables remain the same while response variable are different.
$Model\ 1 - Y_1 = X_1+X_2+X_3$
$Model\ 2 - ...
1
vote
1answer
46 views
What should be the optimal ratio of sample size to the number of parameters in the model?
What should be the optimal ratio of sample size to the number of parameters in the multiple regression model ?
I am wondering as I would like to improve accuracy of prediction.
In some sources I ...
7
votes
1answer
130 views
Coefficients paths – comparison of ridge, lasso and elastic net regression
I would like to compare models selected with ridge, lasso and elastic net. Fig. below shows coefficients paths using all 3 methods: ridge (Fig A, alpha=0), lasso (Fig B; alpha=1) and elastic net (Fig ...
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0answers
34 views
Non-stationary time series modelling - Product lifetime
I would have a question concerning the modeling of a non-stationary time series. I do know some of the models for stationary time series such as AR MA ARMA ARCH or GARCH, but what if the time series ...
0
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0answers
61 views
How to write a loop in R to select multiple regression model and validate it?
I would like to run a loop in R. I have never done this before, so I would be very grateful for your help !
I have a sample set: 25 objects. I would like to draw 1 object from it and use it as a ...
0
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1answer
40 views
Regression - Dealing with Correlated, Zero-Sum Predictors
I'm currently working on a regression problem where a subset of the predictor variables are zero-sum. By zero-sum I don't mean they all sum to zero, I simply mean that increasing one implies a ...
0
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0answers
50 views
Fitting data to the Poisson
As a part of my mathematics research, I am trying to model the traffic in my city.
I have gathered traffic flow count data from highways and city roads. I am using the Poisson model for distribution. ...
0
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1answer
57 views
Not all Features Selected by GLMNET Considered Signficant by GLM (Logistic Regression)
I wanted to create a predictive model of mortality after patients had undergone a surgical procedure. But I also wanted to avoid doing what most researchers do by first performing univariate analysis ...
0
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0answers
40 views
Comparing two models
I have data for the same response variable but measured in two different areas (Ra and Rb). I want to use the same explanatory data (E) to predict each response in turn:
Ra ~ E
then
Rb ~ E
I then ...
0
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0answers
15 views
functional response analysis
This time I have to do several tasks related to functional response.
I want to evaluate the relationship between prey density ($x$) vs prey consumed($y$) the idea is to fit the data set to the ...
1
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0answers
54 views
Building temporal correlation model by a dataset and calibrating the model with other dataset
On one hand,
I have a temperature time series data (dataset1) for a week and I want to build the temporal correlation model by using time-series analysis and performing the prediction for oncoming ...
3
votes
1answer
58 views
How would you explain logit coeficients to someone with no statistical background
Similar question here
The question I highlighted above provides an overview of how generalized linear models work. However, I find people often want more and ask about how the coeficients were ...
2
votes
1answer
45 views
Alternatives to the Baron-Kenny approach to modeling mediation
I'm about to open the door to a very thorny issue in the social sciences. How does one correctly model and test hypotheses about mediating variables using observational data?
I'm familiar with the ...
1
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0answers
47 views
Independent, Dependent Variables, Nonlinear
So, I am not a statistician, but a burgeoning mathematician. Here is something that is perplexing me in statistics, however. My apologies if the question is silly, on one hand, or just not solvable, ...
3
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1answer
128 views
Is the exponential distribution a good model for this data?
I'm trying to determine if the exponential distribution is a good model for a data set that I'm exploring. It doesn't have to be precise. I'm using the data for capacity planning (if it's a good fit) ...
0
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0answers
38 views
Understanding the formula of a model. Translating a statistical model into R code in order to understand its meaning
Here is a quote coming from a biology article:
...
0
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0answers
19 views
Averaging gridded data with missing values
I would like to use various parameters of remote sensing data (i.e. chorlophyl, sea-surface temperature, wind stress, etc.) as covariates in a species distribution model.
I have sightings data, ...
2
votes
1answer
62 views
Fitting data to gamma distribution to find score which corresponds to pvalue < 0.05?
I have data of size 116.667 rows defined as:
...
2
votes
1answer
49 views
interaction terms in separate models?
I'm doing a multilevel mixed model with three cross-level interactions in LMER. Do all three interactions necessarily need to be included in the same model or can I evaluate them in three separate ...
3
votes
0answers
64 views
Build statistical model
I need to build model where y depends on x (y~x). But while I have the usual data for Y, I only have a range of values for X, e.g.
...
0
votes
0answers
23 views
(Population) pharmacokinetic M&S: AUC from sparse sampling in R
I’m relatively new to (population) pharmacokinetic analyses and have a principal question with corresponding programming. I have both an already established pharmacokinetic model and a new data set ...
1
vote
1answer
42 views
How to correctly model noise?
Assume a linear mixing model $x = As$, where $x = (x_{0}, ..., x_{n})^T$ are linear mixtures of $s = (s_{0}, ..., s_{n})^T$, and $A$ is the mixing matrix.
Now, if I introduce additive noise to this ...
0
votes
3answers
126 views
Identify seasonality in time series data [duplicate]
I want to detect presence of seasonality in time series data. I know one can achieve that by plotting the autocorrelation function but I need an automatic process if the series is seasonal or not, ...
1
vote
1answer
41 views
Modeling stimulus-response output
I am trying to analyse some data and I am a bit lost as to what is the correct approach to take.
The data are blood hormone levels, taken repeatedly from various subjects, after a certain treatment, ...
0
votes
0answers
22 views
Distribution of linear model parameters when the outcome variable values are Fisher Z transformed correlation coefficients
I am trying to develop a method for comparing individual correlation coefficients from multiple participants from different groups having performed different conditions of a task.
In terms of ...
20
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9answers
1k views
What is the meaning of “All models are wrong, but some are useful”
"Essentially, all models are wrong, but some are useful."
--- Box, George E. P.; Norman R. Draper (1987). Empirical Model-Building and Response Surfaces, p. 424, Wiley. ISBN 0471810339.
What ...
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0answers
18 views
Distinguishing events from different periodic sources
I have records of the time stamps of events coming from a small number of independent sources. Each source $S$ issues events at a given period $Ts$. Due to some jitter the time intervals between two ...
0
votes
1answer
28 views
BMI at baseline & followup with exposure at baseline; model change or BMI at FUP? Control for BMI baseline?
For a prospective occupational cohort where everyone is exposed to one or more chemical agents, examining BMI at follow-up compared to a specific chemical exposure at baseline, is it necessary to ...
2
votes
0answers
38 views
Modelling rainfall to size storage tanks
I have daily rainfall data for a given site going back about 30 years.
I have a building with an average daily demand for water of $L$ litres and a catchment of $A$ m$^2$ with a runoff coefficient of ...
0
votes
1answer
67 views
Modelling two correlated variables
I wish to simultaneously predict two correlated time series. Here is a plot of one time series against the other:
At the moment I have separate linear regressions for both of them which rely on ...
1
vote
0answers
19 views
jtest vs coxtest
In library "lmtest" The jtest and coxtest functions are used to see if two non-nested models are equivalent.
According to the help function:
...
0
votes
0answers
59 views
How to identify a new pattern in a URL with a machine learning algorithm (Text mining)
I am trying to identify new patterns after analyzing a number of URLs. So let's say, I am investigating the hypothetical website Yoohle.com and their URLs have the following structure.
domain = ...
-7
votes
2answers
167 views
Can you see any S-curve in the scatter plot [closed]
two variables >>> scatter plot >>> relationship >>> ? S-curve!
1) any S-curve?
2) S-curve?
3) if S-curve no scatter plotting?
4) linear correlation=0.85 >>> meaningless?
5) explain the relationship
...
0
votes
1answer
42 views
Fitting models in R with time restriction on coefficients
How should I define a model formula in "R", when one (or more) exact linear restrictions binding the coefficients is available.
Equation: y = b1*x1 + b2*x1
where y = b1*x1 for t < t1 and y = ...
1
vote
3answers
128 views
What model can I use to describe the following time-series?
I'm wondering if someone might be able to help me locate an appropriate model for the following two time-series (the cyan and blue one, the reds are rolling means).
I'm looking more for a general ...
2
votes
1answer
241 views
Comparing models using anova() function in R
From the documentation for anova():
When given a sequence of objects, ‘anova’ tests the models against one another in the order specified...
What does it ...
1
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0answers
11 views
Models for learning acquistion process
Imagine such a memory test for a mice. The mice performs an experiment $E$ with two possible issues $0$ (failure) and $1$ (success). If the mice gets $1$ it is "rewarded", if it gets $0$ it is ...
