# All Questions

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### How to demonstrate biased estimates of linear regression vs cox proportional hazard survival analysis in R?

I want to perform a really simple simulation of right censored data. Then I want to draw a kaplan meir survival curve and do a cox proportional hazards test. Then I also want to perform a simple ...
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### How do you get the principal components of one matrix along the principal directions of another matrix?

Please just don't close this. I really hope someone will be able to give me the answer to this one. I've been trying to work this out for a long time. I have a data matrix, A, on which I have ...
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### When is the t-statistic used?

When and in which context is the t-statistic used: $t = \frac{\hat{\beta} - \beta_0}{se(\hat{\beta})}$ Is it only used to assess whether a parameter in a statistical model is statistically ...
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### Is there a generic expression to represent the multiplication of a distribution?

Let say a value N >> 1 is distributed among m>1 members, which can follow some distribution (Binomial or Gaussian). Is there any generic term to represent the multiplication of the distribution. For ...
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### enumerating patterns in a set of contingency tables

I have a set of 3X3 contingency tables and want to identify the distribution of the patterns by comparing their expected and observed number of samples in each cell using a right statistical test. For ...
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### Classification trees: the best Predictor and the ability to predict

The topmost decision node, the root node in a classification tree is said to be the best predictor of the model. Does this mean the root node variable is also the best in predicting the target ...
13 views

### Help in choosing the algorithm for gaze detection

I am trying to build a program for gaze estimation from the x and y coordinates of the pupil centres, I was thinking of implementing it using artificial neural networks. Here is the high level idea: ...
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### How to simulate noisy respondent entry of short textual responses?

I have a list of company name as following: ...
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### interaction effect on consecutive gestures from different sets

I am conducting an within-subject experiment in which each participant has to perform 2 consecutive gestures with one arm. (with repetitions). To make it simple, let's say that I have 2 sets of ...
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### Interpreting prior and posterior

I am bit puzzled on how we can interpret the posterior. Assume a coin which is 0.1 probable to be unfair. So our prior probability on the coin being unfair is 0.1, and being fair is 0.9. Also by ...
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### Computing Issues with Kriging

I am having some issues with Kriging in R, and I was looking for some idea where I am going wrong. From what I can tell, I done a decent job removing the trend, and I believe my transformed data is ...
18 views

### Do we need to adjust sampling weight in logistic regression?

Suppose, I am using malnutrition data from Demographic and Health Survey. This survey used multistage cluster sampling. Here is a sampling weight (probability weight). If I want to say nationally ...
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### What is the highest density region?

In statistical inference, problem 9.6b, it mentioned "a highest density region". However, I didn't find the definition of this term in the book. One similar term is the highest posterior density ...
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### Minimization of the Sum of Absolute Deviations

My particular task is to show $|Y_i-B_0-B_1X_{i}-B_2X_{i}^2 |$ has more than one min value. We are given $x_1=1$, $x_2=2$, $y_1=3$ and $y_2=4$. I am truly lost, I need to show there are more than ...
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### Non-parametric variogram estimators

I'm working with overdispersed, count spatial data. The goal is to look specifically at spatial dependence patterns. I'm trying to fit variogram models to empirical variograms, however the only ...
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### Pooled and Fixed Effects Results

I use a hausman test to determine whether pooled ols or fixed effects should be used and the results favor fixed effects estimation. But when I estimate fixed effects the results of my main variable ...
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### Constructing alternate hypothesis: How to determine if Ha > H0 or Ha < H0

In Chapter 8, Test of Hypotheses based on a Single Sample, in Devore's Probability & Statistics for Engineering and Sciences, he states that the null hypothesis, $H_{0}$, is the a priori claim ...
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### Meaning of the Boosting algorithm for Regression Trees

I have a problem with understanding the concept of the Boosting Algorithm. ...
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### What are good tutorial on Weighted Finite Automata?

I would especially appreciate papers, books or tutorials with source code already available. Currently I'm reading "Spectral Learning Techniques for Weighted Automata, Transducers, and Grammars" by ...
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### Inconsistent Performance of PCA Results from SPSS

I've completed PCA with my dataset (16 variables) and extracted 3 factors. I then created an Excel spreadsheet where I can enter in user provided data and calculate the scores for each of the three ...
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### Hidden markov model multivariate regression with time-series data

I am working with a dataset that includes the trajectories of various car trips and would like to be able to predict their destinations using only a subset of the trip trajectory. For instance, if in ...
6 views

### R: how does caret choose default tuning range?

When using R caret to compare multiple models on the same data set, caret is smart enough to ...
16 views

### Hazard function, survival function, and retention rate

What is the difference between the hazard function, survival function, and retention rate in survival analysis?
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### Plotting List of Words with R [on hold]

I am an R beginner in way over his head. I am starting with a list of character vectors. It starts with 25 words. Each year some of these words are pruned from the vectors. I want to plot the list of ...
13 views

### Using MCMC to simulate complex process from given parameters

Assume I have a complex Markov stochastic process (think a soccer model), where the scoring intensities change during the match in ways, depending on various parameters. I have it implemented as a ...
23 views

### Merge 3 distribution into one distribution [on hold]

It is possible to merge 3 distribution into one.. I was thinking of something as seeing how much they correlated each other and based on that, come with an $\mu$ and $\sigma$ defining the merged ...
13 views

### Finding conditional distribution in graphical model (undirected graph)

Given that I have a graph $G=(V,E)$ and a set of random variables $X:=(X_v: v\in V)$. I also have the joint distribution of $X\sim p(x)$. What are the ways to find out the conditional distribution of ...
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### k means with binary variables

Is it OK to use kmeans with binary variables? I mean Euclidean distance? I guess the binary variables will be the ones that get the most power to determine the ...
56 views

### Intuitive explanation for when Pearson correlation coefficient equals 1

Whenever I teach a complicated formula, I always demonstrate to the class that it works intuitively in extreme cases. For example, when all the data values are equal, the standard deviation is 0. Not ...
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### Baye's Classifier problem [on hold]

Here's the problem set: I got the first two sections down but I have no idea how to do the third section. Can anyone help?
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### Why do thse two methods yield the same estiamte [with code]?

I am running the following (in R): ...
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### Factorization Theorem for sufficient statistics

I have a question on factorization theorem for sufficient statistics. I understand that to state whether or not a sufficient is statistic, you must factor the likelihood function of the pdf into two ...
10 views

### On the use of the autocovariance generating function

The autocovariance generating function is defined as: $$g_X(z) = \sum_{h = -\infty}^{\infty} \gamma(h)z^h.$$ Where $\gamma(h)$ is the autocovariance function of the considered process $X$. I can ...
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### Interpreting conflicting hypothesis results from anova test

I've created a test where a participant plays a game and must maneuver as many 3 pointed stars to the right side of the screen and 4 pointed stars on the left as they can within a time limit. The test ...
12 views

### Possible Monte Carlo usage for defining t?

I have the following question. As a part of a research, I am trying to determine based on repository contribution factors which users can be classified as core developers, that is, developers that ...
11 views

### How to estimate relative risk for a small group which has 0 members with the outcome?

I have a contingency table that looks like this: ...
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### what to do with ridiculous but valid leverage points

So I'm having some difficulty fitting a linear model to the data (see other post here glm model fit - can't find a family/link combination that produces good fit). In particular, I'm worried ...
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### assigning column name to a data frame by reading a different file [on hold]

I have created a data frame from a pre given data set which does not have column name.so by default the col names are V1, V2.......V42. Now I have one more file (.txt) which has one column with 41 ...
11 views

### Which method for neural network [on hold]

What are the general points for selecting a method for a neural network. I believe, it can be generated with different methods such as lm, glm, randomforest, knn, nnet, neuralnet etc. I have just ...
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### What is the difference between a 2x2x2 split plot ANOVA and a 2-way repeated measures ANOVA? [duplicate]

What is the difference between a 2x2x2 Split-Plot ANOVA and a 2-Way Repeated Measures ANOVA?
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### How to asses significant differences in between participant pretest posttest design?

So, the groups would be control group and experiment group. The scale used is ratio. Both will be given pretest and posttest. So, how should I assess the differences between control group and ...
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### neural network multiple layers feed forward

NN on figure below has two nodes (N0,0 and N0,1) in input layer, two nodes in hidden layer (N1,0 and N1,1) and one node in output layer (N2,0). Input layer nodes are connected to hidden layer nodes ...
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### Value added composition by sector

I am trying to make graph of value added composition by sector based on world bank data (http://data.worldbank.org/indicator/NV.SRV.TETC.ZS?display=default), but when i extracted data for industry, ...
24 views

### Goodness of regression model

What are the main indicators of goodness of a regression model? Are they MSE (mean squared error) http://en.wikipedia.org/wiki/Mean_squared_error , R-squared and adjusted R-squared only? Can mean of ...
6 views

### adding two transition columns to a dataframe [on hold]

Hello I have a dataframe with 1/0 variable, call it remission I also have another column of patient id's i also have another column of recorded times(not time to achieve remission) just time i want ...
13 views

### Interpretation of linear and quadratic interactions

I'm working on building and interpreting multilevel models. In one, I'm predicting binge episodes over time and using a linear time by baseline characteristic interaction as well as a quadratic time ...
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### Can you translate a difference in mean predicted probabilities measure to a percentage? [on hold]

In this study I am looking at , the one variable was negatively associated with the primary variable. Does (-.60) mean a reduction of 60%?