# All Questions

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### How to compare the difference of two time points of two groups

Let's say I want to compare the height change of female students and male students between two time points. I want to know if there is any difference between males and females in terms of the height ...
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### Choose between residual sum of squares (RSS) and comfounded RSS?

In every course I have taken, I was taught to use the residual sum of squares as (part of) the loss function in regressions, either in simple OLS, lasso or other linear regression methods. Recently I ...
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### Trying to understand the math behind Avi Wigderson's simple example

In his celebrated talk on randomness and pseudorandomness https://youtu.be/Jz1UoAWD80Q?t=366 legendary mathematician Avi Wigderson makes the powerful statement that sampling is perhaps the most ...
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### How to find the distribution that minimize the KL distance(divergence) to a known distribution?

Everyone! I'm reading the paper On test marginal versus conditional and I'm a little confused one place in page 9, when the author use "maximum likelihood projection" to get the covariance ...
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### Some body help me to understand SVM [duplicate]

I'm beginner of SVM and have difficulty understanding SVM calculating principle. I want calculate SVM formula by hand using simple example. Anybody help me to understand svm showing calcualting ...
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### lmer with/without covariates of no interests

I am new to using R and lmer model, so the following question may sound dumb to you, but I do have difficulty with figuring that that :( I have this ...
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### Using Inception and FID scores in training?

Is it possible to use the Inception and FID scores in the training of a deep image generation model, i.e. to maximize the scores in a loss function, albeit this is "cheating"? If so, has ...
2 votes
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### Confusion on units for the Poisson distribution when it is used to model variables with units

This question stems from the comment section of this question: Bus wait time under Poisson distribution, where it seems that The properties of the Poisson don't make sense for times because the units ...
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### Frequency and hypothesis

which does it means? the results were processed using frequency tables of data obtained and expected data with a confidence level of 90% and with 4 degrees of freedom. To test the hypotheses, the chi-...
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### Prove $P(X_1+X_2> 2C) \leq P(X_1>C)$ if $X_1,X_2$ are identical, but dependent?

If $X_1,X_2$ are dependent but identically distributed, it seems obvious that $P(X_1+X_2\geq2C) \leq P(X_1\geq C)=P(X_2\geq C)$. At least if we additionally assume that the joint distribution is ...
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### question of a Poisson random effect model

Assume a Poisson random effect model (with a random intercept) $$\log E(Y_{it}|b_i,x_i)=\beta_0+\beta_1x_i+b_i$$ $$b_i \sim N(0,\tau^2)$$ How to derive the population-averaged effect of one unit ...
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### Finding the position of the global optimum with Pytorch

I have a dataset with 22 parameters and I did a PolynomialFeatures = 2 to find the influence of interaction. This was then fitted to an Artificial Neural Network with the lowest loss being around 0.02....
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1 vote
1 answer
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### How to check confounding and mediation in large dataset?

Given a large dataset, one cannot possibly check every model. In particular, it does not seem clear to me that one can check confounding or mediation in either cases. How does one check confounding/...
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### embedding sequences (eg. with doc2vec): do trajectories in the learned (N-dimensional embedding) vector space make any sense?

My data is a collection of temporal sequences of events (each event has a timestamp / or, alternatively, a duration). An example could be sequences of events generated by customers interacting with ...
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### How to interpret a Linear Regression in R

I would like to know how to interpret the result from the regression model as the intercept is coming negative.
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### "Survival" vs. "Hazard" : When to Use Which?

When dealing with Survival Analysis, we create models that estimate two properties: Survival: Survival Probabilities tend to be more straightforward to understand. Survival Probabilities estimate the ...
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### Publishing paper (research essay) on a 'low hanging fruit' topic

I'm considering spending a few hours publishing a short research paper on a cool statistical concept I stumbled onto. Basically I noticed than an average person's parent has more children than the ...
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1 answer
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### Statistical Models for "Prioritization"?

Are there any general classes of statistical models that are able to perform "ranking and prioritization" tasks? For instance, suppose a hospital has: data on patients (e.g. age, height, ...
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### Stratification of the continuous y (target) variable in regression setting

Is it wise to stratify the continuous y (target) variable when you split your training and testing data from the total sample in regression setting? Here is the approach in python to do implement ...
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1 answer
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### How to deal with left truncation in cox model in R

I have a longitudinal data with 5 follow-ups. My aim is to see the effect of a disease on ability decline at old age. In my study, I have sibling pairs, one with disease (1) and one without disease (0)...
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### Can you help me with distribution/Skewness

Can you tell me if the data normal distributed are? It looks a bit strange. I would say it is skewed 40,80 and so on are sizes of the Apartments in m^2
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1 answer
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### Is there a statistical software package for the generalized conditional/multinomial logit model?

I have a discrete choice model of moving from one state to the other, so alternatives=states. I have case-specific variables such as income, race, and gender. In addition, I have moving distance ...
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### Question about a paper on Calculating All Possible Regressions

I am currently reading the paper "Computational Efficiency in All Possible Regressions" by Liu and it mentions the following. A quick explanation of what I understand: We have a set of $k$ ...
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### statsmodels.adfuller weird behaviour of usedlag value

I'm learning about time-series analysis and have two series on which I'm performing an Augmented Dickey-Fuller test in order to check for stationarity. I'm trying to understand why I get very ...
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### Why include fixed effect in cross sectional ols?

Consider repeated cross-sectional data that contains observations in 10 provinces from 2011 to 2015. Each observation is an individual, but the same person is not observed each year, instead, ...
2 votes
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### The probability/cumulative density function for inequality of two random variables

I have two random variables X and Y which came from different inverse gaussian (IG) ...
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### Getting the arc-lengths of projections along a local principal curve in LPCM [closed]

I have been using the R package LPCM to obtain local principal curves (Einbeck, Tutz, and Evers 2005). I would want to obtain the arc-lengths of the projected points from the beginning of the curve, ...
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### How to measure the change in customer flow from brand A to brand B at two points in time (pretest and posttest) after a stimulus?

I am conducting a research in which I have data on the purchase of 4 brands of some consumers in a first period of time (pretest). But I also have the data for the purchase of those 4 brands and the ...
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### Fisher's exact test when resampling from the population

I am using different ML classifiers for making predictions related to a binary classification. I would like to compare two groups. Let's call them A and B. The already trained and tested classifier ...
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### Why is the value of SE for the transformed regression model higher than the initial model with autocorrelation?

Is it right that with positive autocorrelation, the model underestimates the SE. Hence, using generalized differencing, the transformed model has a higher value of SE? And if so, what happens to a ...
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### Getting distances from points to their principal curve projections in R princurve? [closed]

I have been using the R package, princurve, to calculate principal curves. Now I want to obtain the squared distances from the points I used to fit the principal curve to their projections in the ...
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### How can I estimate the variance of the error terms in a conditional/multinomial logit model?

Conditional/multinomial logit models(CML) can be esimated by the Maximum Likelihood Estimation(MLE). The likelihood would consists of choice probabilities: P_{ij}=\frac{e^{V_{ij}}}...
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### Shrinkage / L1 regularization as a loss term versus a constraint (post-process step) with momentum optimizers

I have a complex model with very non-linear operations (divisions, exponentials, matrix inversions, square roots, Cholesky decompositions, etc...) for which I want to optimize the parameters. However, ...
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### Problem formulating a hypothesis test for the mean

Suppose that I would like to support the following hypothesis: h = The average weight of people in New York is 70kg. If I take h to be the null hypothesis then I can only reject it (I assume that ...
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### Why is my kNN performance bad?

I am using the Wisconsin Breast Cancer Data Set from sklearn, and wanted to apply simple classifiers on it. The data labels are binary, has around 31 numerical features and in total 569 instances. So, ...
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2 votes
1 answer
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### Should I join train and validation sets for final NN model training? If yes, when to stop training the final model?

Normally we divide our dataset into 3 sets: train set, validation set, test set. We use train set to find optimal parameters (weights and biases of NN) and validation set to find optimal NN ...
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### How to run a multilevel regression model with crossed random effects: items and participants?

I am trying to run a multilevel regression for my study: I have two random effects; participants (97) and items (which are the 20 words used in the study) Each participant had to spell the same words. ...
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### is nrmse scale-dependent?

Im trying to evaluate my regression models using a normalised version of the RMSE, nrmse = rmse(y, y_pred)/rmse(y, y_mean) where y_mean is the array of the same len as y filled with the mean value of ...
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### How do you get this bifurcation diagram of this 2D discrete time model?

I want to replicate the results of "Chaos in Duopoly Pricing" by T. Puu, which can be found here: https://www.sciencedirect.com/science/article/pii/096007799190045B#section-cited-by. The ...
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### Mean-level forecast from rugarch does not match manual calculation

I am looking into the rugarch package and am trying to understand how the one-step-ahead forecast is calculated. Specifically, I am fitting an AR(2)-GARCH(1,1) ...
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### Estimating Top n Prices points on a given day for a particular product which would maximize revenue

Problem Statement :- On any given date of the year, get top n prices which would maximize the revenue for that day for a particular platform. Dataset :- Date Price ($p_{i}$) Platform $X_{1,i}$, \$X_{...
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### LinearRegression in Pytorch and sklearn, what is the differnece?

I am currently implementing Linear Regression in Pytorch and sklearn and I get two different Mean squared error (MSE) values for both. MSE is lower for Pytorch Linear Regression. Wanted to ask what ...
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### Interpret output for the standardised difference in stata [closed]

I have an output for the standardised difference using the stddiff command in Stata. How do I interpret it?

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