# All Questions

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### Significant difference in percentage values

I am trying to find a significant difference among hormone treatments. My data is a single percentage value for every hormone concentration. How can find which is significantly different using SPSS
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### Combining ordinal multi level (multivariate) indicator variables into one variable

I have a single variable ,for example call it Quality (var x). It contains 2 indicator variables in it ; Efficiency(x 1) and usability(x 2). with each also contains indicator(s). Efficiency (x 1) : ...
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### Impute missing data before or after feature selection?

Will the results of the feature selection be biased if I perform the feature selection before imputing missing data? I have a large data set of 20000 samples and 130 variables. The data sets ...
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### Significant difference between percentage values

I am trying to find significant difference among hormone treatments in a tissue culture study. My data is a single percentage value for every hormone treatment. Can i analyse it using SPSS to find the ...
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### maximum value of $H(X_1+X_2)$

Let $X_1$ & $X_2$ be two independent binary r.v.s, taking values in {0,1}; let $Y \triangleq X_1+X_2$ be their sum, i.e. a ternary r.v. taking values in {0,1,2}. How do we prove that the maximum ...
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### Bias in Factor Score Regression

I'm trying to understand the bias in factor score regression when factor scores are used as observed(independent) variables in regression analysis. I found one paper which talks about this bias. But ...
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### Selecting the best time lagged moving average for time series analysis

I am studying the effect of weather on agricultural outputs. I have yield data from one farm over 5 years and a number of weather inputs (rainfall, temperature, soil moisture, etc.) for the entire ...
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### Is there a name for this simple probability relation? [duplicate]

Namely: $\quad \frac{P(A \cap B)}{P(A) P(B)}$ Cleary this is 1 if A and B are independent, and I think it would be 1/2 if A = B. So it seems like this is some measurement of dependence. Is it ...
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### Terminology: Varying $p$ or “probability” when sampling randomly from a distribution?

Does it have a name, if one varies the $p$ or "probability" when sampling randomly from a distribution to meet some requirements set for the random variables that utilise the values drawn from that ...
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### Constructing a problem-specific loss function

Problem Description I'm beginning network construction for a problem that I feel could have a far more insightful loss function than a simple MSE regression. My problem deals with multi-category ...
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### Identifying Changepoints in Learning Data

I have a "changepoint" problem that I do not understand. The data for my MWE comes from one human player as s/he played the same video game for 31 one-hour sessions (no more than one session per ...
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### How to bin correlated data?

Let's say I have 100 data points $\bf{x}$ with covariance matrix $\mathbf{C}$ where non-diagonal elements are non-zero. Now I have a binning operator $\mathbf{P}$ of dimension 10$\times$100, that ...
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### scikit-learn ExtraTreesClassifier - Why is the pickle file so huge? [on hold]

Using python + scikit-learn, I fit an "Extremely Randomized Trees" classifier (ExtraTreesClassifier) to a ~ 900K sample array of 100 features. I then tried to pickle it. I instantiated the ...
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### Best effect size statistic for ordered categories

I have ordered categories, and a prediction for the size of the categories. If the categories were unordered, I would use Cramer's V as a measure of the effect size. [Feel free to give an opinion on ...
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### Missing Argument m in addModule

I'm very new to python and pybrain and i'm trying to get through the tutorial at http://pybrain.org/docs/tutorial/netmodcon.html. I'm stuck almost at the beggining where i have to add module to my ...
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### Problem with producing valid forecasts

I have a weird problems with producing good forecasts with R and the forecast package. The data I use can be found here: http://pastebin.com/2gwyVYrj Sample code I used: ...
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### Central Limit Theorem- observations vs samples [duplicate]

I'm confused with the concept of central limit theorem and I need some clarification about it, hope you guys can help! Now suppose there is a population in form of numbered balls contained in a box. ...
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### Cluster Analysis with correlated variables

I want to perform cluster analysis. I have 10 variables, and 350 observations. I noticed that a lot of variables are correlated. I have two pairs with over 0.9 correlation, and a few others with ...
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### Better accuracy with validation set than test set

I trained a model with some algorithms like random forest, logistic regression and so on. My dataset was split into 80% CV train data (so actually 60% of data to train the model and 20 % for testing ...
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### Can the mean of ordinal variables correlated between them be interpreted as continuous?

This is probably obvious to most of you but I need to analyse data where a variable is the outcome of a factorial analysis (mean of 5 ordinal variables on a likert scale), more precisely im looking at ...
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### What is the effect of taking the mean of a moments-based estimate?

Suppose I estimate the second and fourth moments of a signal as $M_2 \approx \frac{1}{N} \sum_{n=0}^{N-1} | y_n |^2$ and $M_4 \approx \frac{1}{N} \sum_{n=0}^{N-1} | y_n |^4$ and then I use these ...
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### error rates of knn minimal for k=1

I am trying to find the best parameter $k$ for a nearest neighbour classifier using cross validation for some datasets. After computing and plotting the error rates, I noticed some strange behaviour ...
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### Link between stationarity of AR(2) and stability condition of corresponding difference equation

In the standard textbooks, such as Hamilton (1994), it is stated that the conditions for stationarity of a process $y_t = \theta_0 + \theta_1 y_{t-1} + \theta_1 y_{t-2} + \epsilon_t$ follow from the ...
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### Is it valid to use the full dataset to determine important variables and a partial datasets for training a classification algorithm?

Given a dataset with n variables and a binary outcome: Are there assumption violations/risks to drawing conclusions if the entire dataset is used to determine which variables are valid if the second ...
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### NA values for coefficients in Cox proportional hazards model

I'm doing a cox regression analysis. My model is given by ...
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### Compute partition function

I'm given a distribution on 3 discrete variables $x, y, z$ which is defined as $$p(x, y, z) = \frac{1}{Z} \psi(x, y, z) = \frac{1}{Z} \phi_1(x, y) \phi_2(y, z)$$ where $x, y$ can take up value among ...
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### Probability Homework question regarding 3 friends' salary [on hold]

After graduation, three friends start their first jobs. The monthly earnings of friend 1 have a normal distribution with mean $15,000$ and standard deviation ...
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### Interpretation of posterior probabilities in Bayesian Network with BNfinder

I'm currently using a python library BNfinder http://bioputer.mimuw.edu.pl/software/bnf/bnfinder_doc.pdf where author on page 10 describes the output of posterior probabilities of the interaction ...
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### control variables in panel data regression with stata

I am currently trying to run a regression with panel data in stata but I have difficulty to consider control variables. Is there a way how I can consider control/mediator variables in my panel ...
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### What are all options of graphical user interface for analysis in R? [on hold]

I've created a classifier on my data set using R software by using some libraries. I want to make a GUI for my code so that the ...
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### Issue with weights in R CHAID decision tree [on hold]

I am new to R and as well as stats world. For my problem, I am using CHAID in R to process my dataset and arrive at a decision tree. I am trying to assign weights to each of the dependent variables ...
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### Why is using data or centered data equivalent in ridge regression?

In other words, given two ridge regression problems: $$(b,c)=argmin_{b,c} { \sum_i^{m} (y_i - c - b^Tx_i)^2 + \lambda b^Tb}$$ (\hat{b},\hat{c})=argmin_{b,c} { \sum_i^{m} ...
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### Insurance policies

A portfolio has 100 independent insurance policies.Each policy has a probability 0.8 of making no claim, and a probability 0,2 of making a claim. when a claim is made, the loss amounts are 10,50 and ...
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### How to design this ANOVA formula in R?

I have data with four variables: Treatment (yes/no) Gender (M/F) Ethnicity (Black, White, Latino) Test Score (integer value in set range) I want to know if a treated Black Male had a higher test ...
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### Correct Hypothesis Test

Experiment: At selected intersections an intervention (advertisement) is applied on random days for a 4 week period, the intervention was applied exactly half of the time. Data collected centers on ...
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### Intuitive understanding of this sentence with regards to time series

I am reading the lecture note here by Simon Gilchrist on equity premium puzzle. The risk free rate is not very volatile: σ(R) = 2% per year but is persistent (ρ = 0.6 in annual data) leading to ...
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### MLE - Why assume that there is a true parameter value?

In parameter estimation, we assume that the observed data $D$ is sampled from a distribution $f_{\theta_0} \in \{f_{\theta} | \theta \in \Theta\}$, where $\theta_0$ is the true, unobserved parameter ...
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### Calculating risk ratio using odds ratio from logistic regression coefficient

I have a binary logistic regression with just one binary fixed factor predictor. The reason I don't do it as a Chi square or Fisher's exact test is that I also have a number of random factors (there ...
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### Time course Normalization

I am trying to understand functional connectivity using fMRI data. Can someone explain time course normalization and about its usefulness in general?
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### Right-censored independent variable in Cox/logistic regression

I have a right-censored continuous independent variable that I want to include in a Cox regression. The variable is a physiologic test which is capped at a certain time, say 120 seconds, due to safety ...
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### Multiple Linear Regression: results in training and testing data not correponding to run data

I have 3 data sets each with 1 column of Y data and 20 columns of X predictor variables. Training data which is 2200 rows. Testing data with 550 rows. Run data with 550 rows. I am using linear ...
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### Fine-tuning model parameters in an systematic/optimised fashion

Tuning parameters in R isn't a new topic. I am embarking on some modelling of a large data set, with the goal to create a predictive model using R, selecting predictors analytically from an ...
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### How do i implement a zero inflated poisson inverse gaussian generalized linear model

Having spent a little time in solving these problem. it seems am getting nowhere yet. These are what i found out -the gamlss results is quite different from the zeroinfl function in pscl of R ...
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### Approximate estimation of a covariance involving ratios

I have three random variables (T, O, A) that are each approximately normal. These three random variables are combined to form two ratios: X=T/A and Y=O/A. I wish to get an estimate of the covariance ...
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### Why do the authors subtract the median in this measure for adjusted average app rating?

I'm just reading the paper "Is this App Safe? A Large Scale Study on Application Permissions and Risk Signals" by Chia et al. (available here from ntnu.no). On page 3, they calculate an interesting ...
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### How well does my model fit the data?

I have 3 measurements, and I want to know if there is a correlation between x and y. I use this model to my data, but how can I check if this model is good? If my understanding is correct, it is ...
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### Why are we using ICA? [duplicate]

I am new to Independent Component Analysis (ICA) and have a rudimentary understanding of the method. I understand that PCA finds vectors on which the projected data has maximum variance. ICA, on ...
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### How I can make Markov Chain Model of norm profile by training data? [on hold]

By given some data I have to train this data in Matlab which forms markov chain model, but I don't know how to do it.