A statistical model is a formalization of relationships between variables in the form of mathematical equations. The model is statistical as the variables are not deterministically but stochastically related.

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32 views

A better fit for sinusoidal data

I have been struggling to fit my data to a sine curve. My data looks like: frame = data.frame(hour = c(0, 1, 2, ... 24), value = (numbers between 0 and 500)) I ...
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20 views

Two-Step estimation

I am currently trying to fit a model that has the following properties: (1) data for several years (2) two decisions/equations (probably involved): (a) one that explains an initial choice of product ...
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15 views

How to plot model with forecasts in R? [migrated]

I recently upgraded R from 2.x to 3.1 and I feel like there were some changes that I am not aware of with regards to plotting models. ...
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24 views

Using A Time Series To “Scale” Another

I know the "average theoretical cost per impression" for Jan 13 - Dec 13. I have other monthly time series for "total # of impressions", "total # of clicks" and "total number of conversions" for Jan ...
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17 views

Calculate pdf of complex model

I'm trying to model the distribution of effects of mutations (let's call it s) in evolution but I'm stuck in generating the probability distribution function (pdf) for my model. So, my model is a ...
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1answer
35 views

How to choose the best logit model using step function in R

I have the data below. I was wondering how I could choose the best model fit of logit model using step function in R. Here is the data in R format: ...
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7 views

Compare model performance to distinguish two groups

I would like to compare a sample from the normal population NP to a sample from an "abnormal" population AP. I have several variables measured on both NP and AP, say age, gender, and VAR1, VAR2 and ...
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2answers
121 views
+50

How to summarize knowledge about importance of variables?

Assume that we have 30 features (inputs) each of which can potentially influence the result (output). We try to use the available ("observed") mapping from features to targets to develop a predictive ...
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1answer
17 views

Which models for suitable for integer values of independent and dependent variables

The data set has independent and dependent measurements that are events, and can be counted. What input / output models are appropriate for integer values? So far I've tried linear regression, and ...
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13 views

geeglm not recognizing clusters

I am fitting a geeglm model and it is not recognizing the clustering. my model is ...
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1answer
29 views

graphical representation of fixed effects from lmer

I have run a lmer model in R: ...
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22 views

Adding real zeros to a dataset vs. presence-only modeling?

I have a fisheries dataset for which I have calculated the number of fishing sets in each grid cell (100 km x 100 km) for each month of every year. Fishermen in this fishery are legally required to ...
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11 views

How to decorrelate residuals in r from the covariance matrix

I fit a geeglm model with clustered data and now I would like to decorrelate the residuals of the model in order to run model diagnostics. I read that if I can obtain the covariance matrix of the ...
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1answer
63 views

Are these data underdispersed? If so, what mechanisms may explain this?

Say someone who is well practiced (appears to have reached a performance plateau) shoots 20 free throws on 15 different days and is successful the number of times shown in the upper histogram (...
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18 views

log-linear models and exponential models?

What is usually referred to as "log-linear models"? Is a log-linear model an exponential model where the normalization constant is 1? (since its logarithm needs to be a linear function.) Or is there ...
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0answers
23 views

How do we calculate the $R^2$ statistic for a mixed model with one random intercept only?

I have read in previous posts that for mixed models with random intercepts only, the statistic for $R^2$ is $$R^2 = \frac{\text{V of intercept only model} − \text{V of full model}}{\text{V of ...
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1answer
26 views

How do models, parameters, specifications, restrictions and assumptions relate?

So this has been something I've been struggling with for a long time: The specification of a particular model is subjective. However, there seems to be objective ('true') values of the parameters we ...
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0answers
20 views

Transformations in Simple Linear Regression [duplicate]

Suppose a linear model for Y in a single predictor var, X. If the residuals show a pattern of increasing variance (wrt X), sometimes a transformation of Y, Y'=f(Y) is considered (where f is sq rt, ...
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17 views

Assumptions on a multiple linear regression model and elastic net

I am interested in using elastic net regression in place of an multiple linear regression. I know when you perform a multiple linear regression you should check the assumptions such making sure the ...
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0answers
24 views

How to choose the best regression model?

I have entered main effect terms in Block 1 and interaction terms in Block 2. Based on their beta values, the main effect terms were not significant in Block 1 and the interaction terms were not ...
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0answers
23 views

How can I assess if a parametric model can reproduce the same curve with different parameters?

I have a parametric model that I think it is "degenerate" in the sense that I can obtain the same model with different parameters. For example, if I have a convolution of two 1D Gaussians (say, G1 ...
2
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2answers
258 views

Was this the appropriate regression model?

I was recently proof-reading a friend's thesis (for their writing, not stats usage) when I came across a usage of a regression model which I would regard as incorrect. However, I'm pretty new to the ...
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9 views

Linear model for RCBD

Hi i am told to write a linear model for my stats assignment under an RCBD. ...
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20 views

Do assumptions for estimators affect population parameters?

TL;DR: Specifying a model (a collection of restrictions over a sample space) specifies the model parameters. Specifying an estimation procedure adds additional number of restrictions (assumptions?). ...
2
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1answer
14 views

Repeated measures - sum of biomassproduction

I am student in biology. For my examination I conducted a greenhouse experiment with gras. Actually I am not sure how to develop the correct model and unfortunately I haven't found an answer in the ...
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28 views

Fitting a model to data for prediction - best choice for data

I have some data I need to fit a model to that can be used for prediction (interpolation). The data is summarized by the plot below. The black line is x=y. I want to be able to fit a model so as I ...
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0answers
17 views

Model Averaging

Good Afternoon, I am working on model averaging of data collected about bird species and habitat vegetation. I have been using the MuMIn package in R and have taken a subset of all possible models ...
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1answer
431 views

Why should we use t errors instead of normal errors?

In this blog post by Andrew Gelman, there is the following passage: The Bayesian models of 50 years ago seem hopelessly simple (except, of course, for simple problems), and I expect the Bayesian ...
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6 views

given a set of pairs of graphs, build a model that accept a graph and predicts it matching graph

Training Data I have a set of pairs of normally distributed graphs, each with a concrete last sample (maximal X) Question I want to build a model (formula) from the data input: a single graph ...
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42 views

How to interpret ANOVA output comparing two models

I'm working with the Blackmoor data from the study "Female adolescents with anorexia nervosa and their parents." I've made 4 models based on this: ...
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35 views

Reverse engineer a predictive model from a time series graph

I have found some real estate plots in a scientific article. These graphs mainly describe, the believes of the author of the development of the real estate market in the future for certain countries. ...
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1answer
43 views

Correct numerical result in Bayesian model comparison

I was wondering how to calculate the following Bayesian model comparison. Suppose you have a couple of models: $$M_{1}: x \sim Bin(n, \pi); p \sim Be(1,1)$$ $$M_{2}: x \sim Bin(n, \pi); p \sim ...
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0answers
12 views

How to take care of the percentage/rate of an absolute number as independent variable?

I am working on a mixed model, where suppose I have several stores of different sizes. The number of products manufactured in each store is different, say one store can manufacture 100 and other can ...
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1answer
26 views

Definition of Parameters [duplicate]

I imagine this either extremely simple or extremely complex. I am trying to understand the interpretation of the term 'parameter'. A couple of quick online searches deliver an intuitive understanding ...
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0answers
12 views

Comparing goodness-of-fit across conditions

I have repeated-measures data. Participants complete both Stage A and Stage B (random ordering). I have two complex models, Model 1 and Model 2, which are fit using optimization techniques. Model 2 is ...
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16 views

How to measure classification accuracy based on presence only data?

I have a binomial GLMM which I calibrated with data on recreational visits (presence) compared with random controls where no visits were recorded (absence). I generated the controls myself, whereas ...
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1answer
41 views

Goodness of fit: observed vs simulated data

I have a set of 2-dimensional "observed" data of sample size N: $$O = \{(x_1, y_1), (x_2, y_2), ..., (x_N, y_N)\}$$ The hypothesis is that $O$ is a realization of ...
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0answers
14 views

How can I validate if a pattern is meaningful?

I am a financial analyst for a construction company. My goal is to develop an accurate sales model that is correctly reflects prior sales history (back testing) so I can then predict future sales. I ...
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1answer
22 views

Correct application of linear regression models from different types of features

I want to build a predictive model of a value which changes over time from features which can be partitioned into 2 types - 9 features which describe the history of the value (And could be used to ...
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1answer
35 views

Assessing residuals from a regression model

I am trying to understand what the residuals from a regression convey about the model's adequacy/ability to explain the variance in the data. I read that if we are able to take the residuals from a ...
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0answers
13 views

How to model data

I am attempting to model a specific variable's sensitivity to a feature set. In concrete terms, I am trying to predict the duration (PAUSE_KS) of a letter (...
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1answer
153 views

What if the trend is changed?

I want to forecast tourist arrivals using time series analysis. I expected to use monthly data from 2000-2013. But due to the civil war, the trend was changed after 2008 as in the following plot. ...
2
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1answer
20 views

Percentage Beyond a Given Value for Empirically Defined Distribution

It is my understanding that standard deviation does not work well as a measurement for distributions that are heavily skewed. If I have a heavily right-skewed distribution, should I simply use the ...
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1answer
11 views

What method should I use to model simplified performance

I have the data of some build times. These builds occur on a cloud and the runtime has been more varied than in the past. One thing that could be occurring is an improper sharing of resources ...
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1answer
26 views

R- predict payment day (1-31)

I need to predict payment day of the month (1-31) for each client (I have at most 9 month of payments and on average is 5). I have both categorical variables and numerical. I tried to use rpart to do ...
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3answers
103 views

backward selection multivariate analysis usind R

I want to perform an exploratory Cox regression analysis of medical data using R. I am practicing using the pbc data from the survival function. How would you recommand performing a backward ...
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0answers
10 views

Managing/maintaining multiple models

Sorry for posting a vague problem statement, but this is very practical issue i am facing right now and couldn't any hint/solution. My use case is that while trying to build regression model, there ...
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0answers
22 views

Fitting data in multivariate Gaussian

I have a dataset of N*d feature vectors and I was asked to fit them in a multivariate gaussian, with a matlab function (that someone else has programed) that recieves the number of points, mean and ...
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2answers
76 views

Rate of change for the regression model $Y^{\frac{1}{2}}=a+b_1*log(X_1)+b_2*X_2^{\frac{1}{2}}$

Hello I have the regression model $Y^{\frac{1}{2}}=a+b_1*log(X_1)+b_2*X_2^{\frac{1}{2}}$ which works very well however I am trying to interpret it in terms of change for each different $X_i$ term. I ...
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1answer
38 views

Saving each step of Backward selection in R

I'm trying to recreate Leo Breiman's work http://www.stat.washington.edu/courses/stat527/s13/readings/BreimanSpector_1992.pdf and I'm experiencing some major difficulties in R. I've made it that far ...