# All Questions

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### What determines the cost function / how to find the cost function to use

I'm starting to learn a bit about gradient descent, and that method attempts to minimize the cost function. I've seen examples using linear regression, and the corresponding cost function, but now I'm ...
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### Cronbach's Alpha - reliability

In psychometric tests, we sometimes are instructed to end the test after the child has failed a determined number of questions. Thus we end up with children who answered 30 questions and some who ...
139 views

### Estimating the prediction variance in kernel ridge regression

I'm trying to estimate the variance of predictions for a kernel ridge regression model. The model is simply kernel ridge regression: $$\hat{y} = K(K+\lambda I)^{-1}y = A y$$ $K$ is the $n \times n$ ...
490 views

### SOM clustering for nominal/circular variables

Just wondering if anyone is familiar with clustering nominal inputs. I've been looking at SOM as a solution but apparently it only works with numerical features. Are there any extensions for ...
454 views

### How to draw fitted graph and actual graph of gamma distribution in one plot?

Load the package needed. library(ggplot2) library(MASS) Generate 10,000 numbers fitted to gamma distribution. ...
148 views

### Logistic Regression: Does my model selection process make sense?

This is kind of a broad question and so I am okay with broad or general answers. In fact, each of these could be their own individual questions, but I think it makes sense to ask them all. Even if you ...
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### What does it mean to say that an event “happens eventually”?

Consider a 1 dimensional random walk on the integers $\mathbb{Z}$ with initial state $x\in\mathbb{Z}$: $$S_n=x+\sum^n_{i=1}\xi_i$$ where the increments $\xi_i$ are I.I.D ...
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### What should I expect biweight weighting values to be?

I am working on a project that involves taking the biweight sample variance of a velocity dataset. This is defined as $\sigma_{BI}^2 = N\dfrac{\sum_{|u_i|<1}(1-u_i^2)^4(v_i-\bar{v})}{D(D-1)}$ ...
427 views

### Boundary or threshold test for regression-type scatter plot

I am looking for a way to test whether a boundary threshold exists in a physiological response – a sample of the data is plotted below. My hypothesis is that the X-variable imposes a physiological ...
22 views

### internal reliability

I have been searching for information on how to conduct internal reliability assessments but have been unsuccessful. Is there a book or website that can inform me on how to conduct these analysis? I ...
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### Support vector data description (SVDD) [on hold]

How can i explain the dual of the SVDD method?. what's the influence of linear term on the dual objective function?
26 views

### Modelling binomial data with censoring in dependent variable and in independent covariate

I am working on a problem in which I have multiple pairs of currently living males i that each have a presumed paternal ancestor ...
338 views

### Normalized RMSE

I have several time-series in a VAR(1) and, due to some of them haven't the same unit of measure, I'd like to estimate the RMSE in percentage. I know that it could be done in several ways (see below) ...
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### internal reliability scores below .70

When one is assessing the reliability of one instrument and the value is under .70 and you then eliminate the item/items that are mentioned that if eliminated would increase the reliability score, ...
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### Confront % changes over time in a time series split by categories

I am working with a problem where I have a time series of sales data and I can look at this data across different categories (for example I can look at sales data over time categorized by products). ...
16 views

### Neural network input values belonging to classes

I need help on configuring a neural network. I would like to pass in accelerometer values (x,y,z) from two different sensors, and have the network compute the corresponding angle. I am providing close ...
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### Calculate EER from FAR and FRR?

I'm wondering if we have FAR and FRR scores for each threshold if we can compute an EER programatically? Say we have: ...
18 views

### Finding correlation between nonlinear variables sets & forecasting

I have two data sets. Data Set A is % over/under budget for a list of non-related projects. Data Set B is % over/under time for the same list of projects. Here is a sample of the data Will I be ...
21 views

### Interpreting the regression coefficient when the regressor is polychoric-based principal component

I have a regression where I am trying to interpret the regression coefficient of the first principal component on some outcome variable. The component scores variable was obtained in a polychoric ...
387 views

### What is an intuitive explanation for how PCA turns from a geometric problem (with distances) to a linear algebra problem (with eigenvectors)?

I've read a lot about PCA, including various tutorials and questions (such as this one, this one, and this one). The geometric problem that PCA is trying to optimize is clear to me: PCA tries to ...
15 views

### Getting an error message “(subscript) logical subscript too long” when training SVM: Issue w/ different Levels within train/test set [on hold]

From some gene expression data I created a 60row x 7134col data frame that includes the gene expression levels (numeric), ...
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### Minimum sample size to check second order stationarity

I can understand second order stationarity refers to weakly stationary processes in which mean, variance, and autocovariance do not depend on time. But is it possible to check weak stationarity/second ...
9 views

### How does imputation affect significance test power?

There are many different imputation methods that make different assumptions about the missingness of the data (MCAR, MNAR, MAR). Since this assumption may not be met, I'm interested in knowing how the ...
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### Estimating correlation(covariance) matrix when fitting a copula using R copula package [migrated]

I have a question about the R package copula. When using fitCopula to fit a copula to data, ...
6 views

### natural breaks arcpy [on hold]

Is there any chance I can create a simple python script to classify my data as Natural Breaks? I have only created a script for quantile classification, but it is not enough for my work. ...
12 views

### Correlation with seasonal data

I've got 5+ years of data, with multiple observations per week. I'd like to understand if there is a correlation between my dependent and independent variables. The catch is that I know this data is ...
83 views

### How can I experiment with Lagrange multiplier in PCA optimization?

Suppose we want to solve following optimization problem (it is a PCA problem in this post)  \underset{\mathbf w}{\text{maximize}}~~ \mathbf w^\top \mathbf{Cw} \\ \text{s.t.}~~~~~~ \mathbf w^\top \...
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### Covariance Matrix for Time Series

I'm trying to investigate how events affect the stock market through econo-physics and I came across a paper that uses the co-variance matrix. What I don't understand is how such a matrix can be ...
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### Are estimators of heterogenity variance and of the random-effects mean asymptotically independent?

In random-effects meta-analysis, there are many different methods for estimating the across-study heterogeneity, $\tau^{2}$ (including DerSimonian-Laird's moment estimator, ML and REML estimators, and ...
169 views

### Machine learning tutorials / examples on data sets larger than a terabyte

I am trying to gather a list of practical ML examples / tutorials on more than a terabyte of data. I'm particularly interested in feature extraction from large data sets that involves aggregation (the ...
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### Dataframes of different lengths [migrated]

I'm looking at the time series of the DJIA and FSTE100 but they are not of the same length because of trading days. How can I fix this in R? I saw a code snippet and I tried to adapt it must my data ...