# All Questions

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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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### Which method for neural network

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?

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, ...
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### 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 ...
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### 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 ...
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### 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%?
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### Overlap between two normal pdfs

I have two normally distributed random variables (estimated from two different sets of samples), and I'd like to know how "similar" those variables are (in order to compare the sets). I had the idea ...
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### How to show that the condition of one hand predicts the condition of the other hand

I have this kind of data: subject hand condition s01 left 1 s01 right 0 s02 left 2 s02 right 2 .. .. .. ...
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### Which phrase is correct? “Out of sample” or “Hold out sample”?

Which one is correct phrase for data that model didn't see? For example i trained my model based on data-set from 200 to 2002. Now i want test my model using 2003 data-set. Which phrase is correct in ...
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### Linear distribution of degrees around a circle

I am trying to fit a model using wind data (0, 359) and time of day (0, 23), but I am concerned that they will poorly fit into a linear regression because they are not themselves linear parameters. I ...
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### Using count data with number of days

I have two populations A and B. The data consists of count data per number of days after an event has occurred. For example: ...
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### repeat measures, continuous/scale data, 3 dependent variables, 7 independent

Children played a comprehension game on an iPad and their attentional patterns were observed and coded for using video coding software. The duration of 7 different behaviors were coded for. Pupils ...
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### Python: In which cases will random forest and SVM classifiers can produce high accuracy?

I am using Random Forest and SVM classifiers to do classification, and I have 18322 samples which are unbalanced in 9 classes (3667, 1060, 1267, 2103, 2174, 1495, 884, 1462, 4210). I use 10-fold CV ...
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### What could be causing vertical trends in residual plots?

I'm fitting a mixed effects growth model and after fitting the model with a simple covariate term and random effect I get the following residuals: If I add in a quadratic term, I'm able to remove ...
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### Are there any possibilities to check model assumptions or any diagnostic for the proportional hazards model with correlated times?

As far as I know, regular proportional hazards model have assumptions that times have to be independent, hazards for each variables should be proportional and there should be noninformative censoring. ...
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### How can a univariate seasonal time series be made normally distrubuted by Box-Cox transformation?

I'm trying to fit a sarima model on the univariate data with 180 points (periodicity=12). I use the auto.arima function in R. After fitting a model to the data, the only problem is the violation of ...
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### Error in predict function when training set and test set have different columns [on hold]

I have a dataset which I split into a Test and a Train . On the Train dataset I have done a few preprocessing steps such as Imputing missing values, dummyfying variables, and also added a few extra ...
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### Random Walk Probability Including Drift

What is the equation for the probability of a random walk with drift being equal to a specific value after n steps, given a specific standard deviation?
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### Large samples and normality of residuals

Ok I understand that normality of residuals is not really a concern in large samples. But can anyone tell how large should the sample be to ignore normality. Any cut off point? I'm working with a ...
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### distribution of GPAs

Often colleges/university opt using 'relative grading' mechanism for their students. Since we know that scores given to students on their examinations follow gaussian distribution thus grades are ...
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### MLE for panel data

I am a beginner in statistics, so please don't mind if this question sounds elementary. I am trying to analyze monthly panel data with number of hospital admits in a town. I have data for ~5000 ...
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### Determining parameters for distribution of standard deviations

I have a database of 10-star movie ratings (similar to IMDB), with a large number of movies and an also large number of ratings for each movie. For each movie I have computed the mean and stddev of ...
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### Will using Mann Whitney U test, comparing the medians, give a valid inference to the populations being compared?

I am basically comparing the length and/or weight of an animal categorised by the presence or absence of a specific allele, so I have two groups. The data for length and weight do not seem to be ...
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### Estimating Markov Switching Probit

I attempt to fit the following probit model to a time series where we observe the binary variable $R_{t}$ and another variable $X_{t}$, a latent unobserved variable $y^{*}_{t}$ and a state variable ...