# All Questions

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### When Should The Following Tests Be Run

What are the assumptions behind each of the following types of tests (i.e. what are the prerequisites to running each test). Paired-t Sign Two-Sample t Pooled Two-Sample t Two Proportions F I ...
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### Average of arrival times excluding outliers

I'm working with a dataset of arrival times as below: ...
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### Equal variance assumption in factor analysis

How can we check this assumption? Sample variance? What if it doesn't hold? Do we have alternative?
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### Writing R Function To Determine Which Statistical Test Should Be Run

I am trying to write a function in R that determines which of the following statistical tests should be run on a set of data: {paired-t, sign, two-sample t, pooled two-sample t, two proportions, F} ...
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### two sample mean comparison with small and nonnormal data

I have three groups. Both have small sample sizes (<10). And we can't check the assumption of normality. I want to compare any two of them. What to do in this case( unequal small sizes, ...
37 views

### Conditional Distribution over the unit disc

How can I show that, $U$ and $V$, two independent uniform $(-1,1)$ random variables have a conditional distribution, given that $U^2 + V^2 <1$, that takes the form: f_{U,V|U^2+V^2<1} ...
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### What is an F test

Would someone please tell me what an F test is and what is shows? Also what is an alpha? And how do I evaluate the p values? I posted two questions earlier and one was 'put on hold' because it was not ...
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### Generating samples from Copula in R

Suppose I want to model dependence between $d$ r.v.´s $Y_1,...,Y_d$ with the copula $C_\theta$, where $\theta$ are the corresponding parameters of that copula. I've also determined the correlation ...
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### What happens when SEM is conducted with a rank-based DV?

Can SEM be conducted with a rank-based dependent variable? If so, which software package would be the way to go? Obviously, you'll get LISREL output and such, but I'm concerned as to how the ...
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### Build a recommender system in weka [migrated]

I want to build a recommender system that needs to work online. I have a very large database of music, with about 40 features per song. These need to be clustered and then a few songs need to be ...
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### about construction of simultaneous test envelope

According to Davison and Hinkley's book "Bootstrap Methods and their Application", page 154, based on an RxN array where R=999 ...
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### Question regarding these two regressions from Stata

the variables in these regressios are: gpi: Gross Private Investments gps: Gross Private Savings Year, Dummy variables: recession81, recession07 I have regressed gpi on gps year recession81 ...
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### Distribution of three dependent random variables

I have three dependent random variables $X_1$, $X_2$, $X_3$, ($X_i\in\left[0, 1\right]$) that satisfy additional condition $\sum_i{X_i} = 1$. If (marginal) distributions of $X_i$ ($i = 1, 2, 3$) are ...
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### When to use Bayesian parameter learning, when others?

Is there any general suggestion as when to use Bayesian, and when other inference approaches?! For example in the case of CRFs, when to use ML [1] and when to use Bayesian approach [2] ? [1] ...
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### Interpretation of regression data, RMSE, and model predictions

I am doing an analysis where I am using one data set of 12 rows (Mold), and running a linear regression analysis on this data set to generate two different linear regression equations. From there I ...
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### Formal statistical test for comparing likelihood distributions obtained via MCMC

I am trying to formally compare the distribution of the likelihood values generated using two different models with marginal posterior values of the parameters obtained using MCMC in order to assess ...
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### Principal component analysis with time series

When you do a Principal Component Analysis (PCA), your dataset generally looks like the following one: ...
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### looping to get basic stats [migrated]

I'm looking for a way (code) to speed some of my routines in R. Since I've no skills with programming, I'm trying some help herein... The question is: how can a use/set up a loop to get the mean ...
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### Plotting a function in R [migrated]

so I'm doing QDA on some data and I need to plot a decision boundary in r ,or MATLAB, which looks like the function below. 0.651 - 0.728(x_1) - 0.552(x_2) - 0.006(x_1 * x_2) - 0.071(x_1)^2 +.170 ...
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### What does a p value of 0.7447 in an F test mean? [duplicate]

I have used R to try to discern differences between male and female students and their preferences for chocolate. My data is not normally distributed, and data transformations failed to 'squash' the ...
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### Is it ever appropriate to put dependent variables in a model when they calculate the independent variable directly?

Is it ever appropriate to fit a multivariable regression model with dependent variables that directly calculate the independent variable? For example, I know that fitting a model to predict BMI by ...
39 views

### Understanding the results of an F test in R

I am performing the test to see if there is any differences between the preferences of chocolate for male and female students. My null hypothesis is that there is no difference. My data is not ...
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### Learning curves and SPSS

I followed a course on machine learning. The analysis of learning curves on the cross-validation set was recommended, as a way to see in what respect your model can be improved (more data, more ...
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### Is the MCMC simply a probabilistic gradient descent?

I'm learning about Markov Chain Monte Carlo methods, and to my undifferentiated mind, they basically resemble gradient descent with a stochastic component replacing the gradient computation. Is this a ...
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### R - what command to generate confusion matrix using as input results from rpart() and predict()? [migrated]

What command should I use in R to perform a confusion matrix after having used rpart() and predict() commands to generate a ...
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### should the sample be homogenous for developing a tool supposed to be generalized across 4 countries??

I am planning to develop a new tool and planning to use it across 4 countries. For the tool validation, is it right to include sample from very large population of 4 countries? Will it affect the ...
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### graphical and statistical approach to evaluate the skewness and kurtosis of a data set

In practice, we may always be asked to check the skewness and kurtosis of a data set. I have two questions. Given a probability distribution, how can we determine/evaluate the skewness and kurtosis ...
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### Sum of variances from regression coefficients, larger then total variance. Why?

For a linear regression fit for a problem with p variables X_i ranging between 0 and 1, where p>20 (I don't know if that is relevant or not), and the number of samples is about 1000, I wanted to ...
28 views

### Word association

I'm doing an experiment with moodcongruency (influence of mood on word retrieval). Prior to inducing a mood, the participants will memorize a list of words containing an equal amount of positive, ...
22 views

### Hypothesis test between ordered categorical independant var and continuous dep. var

Is there a standard hypothesis test for differences in the mean of a continuous dependent variable with respect to a single ordered categorical variable. By specifying that the independent variable ...
34 views

### 5-sigma anomaly problem

Struggling with how to start this question: A factory processes chickens with masses between 1.5 and 2.5kg. "Natural" chickens have masses equally spread across this range. However, "GM" chickens ...
32 views

### Multiple linear regression question

I am running a multiple regression of the form Y = $\beta_0$ + $\beta_1$*$X_1$ + $\beta_2$*$X^2_1$ + $\beta_3$*$X_2$ + $\beta_4$*$X_3$ on a time-series dataset. I want to plot the relationship ...
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### Analyzing within subjects time-limited factors

I have 2 x 2 x 2 mixed design with two between subject factors (sex, organizer) and one within subjects factor (task). The last factor has values for task 1 and task 2. Both tasks were timelimited, 3 ...
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### ANOVA repeated measurements

I am a master's student, and I need your help. I did experiment on one group of rats, the group was tested during 8 days, this is the first stage. The same group was also tested again but this time ...
18 views

### Measure for Separability

I have a (binary) classification problem where after merging single training data points (that can be tracked back to the same source) into aggregates, test accuracy (on single data points again) ...
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### How to print answer in matrix form? [on hold]

We need to analyze normed sum Zn=(Sn- n*EX1)/sqrt(n*DX1). In this case Sn is the sum of independent identically distributed random variables X1,X2,...,Xn. We need to compare P(Zn <= x) and Φ(x), ...
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### A gallery of charts, diagrams, and plot types

What would you recommend as a comprehensive gallery of data presentation techniques? A source that could be used to refer to while you're thinking about better ways of presenting your data? I've ...
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### References for spatial modeling with Bayesian belief networks in medical applications

I want to do research in spatial data mining where I want the concept of Bayesian belief networks applied on a medical domain like, for example, cancer. I have been searching for recent papers in ...
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### Reporting p-values $\le$ 2.22e-16

For some tests in R, there is a lower limit on the p-value calculations of 2.22e-16. I'm not sure why it's this number, if there is a good reason for it or if it's just arbitrary. A lot of other stats ...
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### Machine Learning techniques for classifying response from several continuous factors

I have some data with rows corresponding to male-female pairs, with 8-10 continuous factors (that have been unfortunately anonymized) that apply to both the male and female, and whether they became ...
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### Is there a difference between 'controlling for' and 'ignoring' other variables in multiple regression?

The coefficient of an explanatory variable in a multiple regression tells us the relationship of that explanatory variable with the dependent variable. All this, while 'controlling' for the other ...
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### Class labels in data partitions

Suppose that one partitions the data to training/validation/test sets for further application of some classification algorithm, and it happens that training set doesn't contain all class labels that ...
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### error in logistic regression

I am new to this forum and beginner in Matlab implementation. Kindly, if some one can help me out why my accuracy isn't increasing in training. My problem is as follow: Implement an optical character ...
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### Regression or Manova?

I have the following problem: I have one manipulated IV (degree of co-creation) based on three surveys "no" "low" and "high" degrees of co-creation. Furthermore I have 4 DV (Purchase intention, ...
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### Estimate duration using categorical data

I have a dataset of tasks. Each task: has a duration (difftime in seconds) belongs to a project (project name factor) has an owner (user name factor) In R , I can simulate my data by something ...
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### Coefficients and Standard Errors

We have a last assignment for my poli sci stat class and these two have really got me stumped. We really didn't go over multiple regression very well so if anybody can help, I appreciate it! Your ...
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### Does the central limit theorem imply the law of large numbers

Assuming that the distribution has finite variance (a condition not required for the LLN), then doesn't the LLN follow from the CLT?
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### How do you “control” for a factor/variable?

To my understanding, "Control" can have two meanings in statistics. Control group: In an experiment, no treatment is given to the member of the control group. Ex: Placebo vs Drug: You give drugs to ...