# All Questions

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### Hashtag correlation [on hold]

What is the formula please to calculate the occurrence between 2 hashtags like in the hashtagify.me website please ?
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### Negative variance result when calculating standard deviation

Please note, I am still in secondary school so please keep your answers simple. A question on my homework states to calculate the standard deviation from a given frequency table with several class ...
3 views

### parzen window real examples?

I would like to study Parzen Windows in more depth, do some practical work on it and have been researching about it. I get the concept and all but when it comes to ...
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### Is simple statistical analysis of correlational data for the purposes of prediction practiced? Is it recommended?

I want to implement a facility in my web-app which marks user contributions that, relative to the contributions which respectively precede them, have a high likelihood of being acts of vandalism. The ...
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### Is it correct to compare likelihood ratio indices between logistic regression and multinomial logistic regression models?

In the paper "Including Transfer-Out Behavior in Retention Models: Using the NSLC Enrollment Search Data" (http://www.studentclearinghouse.org/colleges/files/ST_UofMD_casestudy.pdf) the author ...
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### Anova on repeated measures

I'm stuck with an Anova analyisis on repeated measures. I have the following dataset in long format After a meal, each subject in the study filled a nutritional questionaire on that meal. In ...
16 views

### How to interpret the lme function result?

the following is the command I used and the results I got for my question, whether the visitation frequency of my bee is different in different experiment types in different locations. I used the lme ...
29 views

### Does practical insignificance mean no relationship?

I have two problems: 1) I have a regression coefficient that is very significant (large dataset), but has low practical significance. Can I say there is no relationship? And I mean really tiny, like ...
19 views

### Can I obtain the means for two groups using their mean difference?

I have a study which provides the mean difference for two groups (alongside 95%CI, SE, n and p-value). I would like to extrapolate the raw means to use in Revman to perform a random-effect SMD ...
36 views

### Hyperparameter optimization with random search

I would like to do a random search for hyperparameter optimization. The procedure can be found in link. One possibility is to define a fine grid and take random combinations. A better approach would ...
38 views

### negative binomial modelling for child pedestrian accidents

I am currently try to model child pedestrian casualties for each ward in England and to create a model that will predict how many casualties per area based on social and economic qualities of the area ...
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### AR-GARCH mortality model estimation [on hold]

I am working on the paper "Age specific copula ar-garch mortality models". I want to know the stimation procedure in R or in MATLAB? The AR(n)-GARCH(1,1) model is: ...
19 views

### Adding dummies as control variables change the coefficient

It has been difficult to formulate a title for this question. But here is something that is puzzling me. I have an ordinal probit model with a bunch of covariates. One of the covariates is the number ...
23 views

### How does one visualize the self-organizing map of $n$-dimensional data

I have a data set consisting from $7$-dimensional data points. I want to produce a self-organizing map for this data to see how my data is clustered. I have been reading some tutorials from the ...
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### Interpreting pvalue by confronting the observed difference with the expected one (minimum clinically important difference (MCID))

Let's say I study the association between a dichotomic variable (a treatment) and a quantitative one, which is my primary endpoint Let's say I know the minimum clinically important difference ...
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### Critical values for Dickey-Fuller and Engle-Granger tests

I have two time series $\{X_t\}$ and $\{Y_t\}$ both of which contain thousands and sample data and I would like to test whether their stationarity and whether they are cointegrated. I plotted a ...
35 views

### To perform the right Correlation test

I have a data.frame in R where head(data,3) gives ...
30 views

### Which metric is used in the EM algorithm for GMM training ?

My question concerns the expectation-maximisation algorithm used to estimate the hyper-parameters of a Gaussian mixture model in z multivariate setup. I understand that the EM algorithm uses the ...
15 views

### DTW time warping with time series: statistical soundness

taking off from this topic here (Hierarchical clustering, linkage methods and dynamic time warping) and from this (Dynamic Time Warping Clustering) I was wondering if anyone could tell me what could ...
61 views

### Simple question about Ornstein-Uhlenbeck process

My question comes from this paper. The picture bellow provides a summary of the equations. Suppose prices of two stocks satisfy (2.1) SDE. Then X(t) is expressed as (2.2) and can be modeled with as ...
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### Should I use a VAR or VECM to model a time series in which one variable is stationary?

I was wondering which of the above two models would be most suitable. I'm modelling the relationship between interest rates, unemployment, CPI, GDP and London house prices (all UK data). I was going ...
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### What type of statistical analysis do I use now [on hold]

I'am doing doing work on which type of stretching is best dynamic vs. static, I measured the distance in a sit and reach test before warm up then completed 2 measurements after the warm up, I have put ...
6 views

### Comparing the effects of variables that have the same nature

I'll try to illustrate my question through an example based on a study I'm carrying out right now, but I think it can be interpreted more generally. I'm interested in assessing the effect of some ...
9 views

### periodicity within Signal [on hold]

I am actually measuring the current of a dc motor, it takes values between, and I want to be able to find periodic peaks within my signal. My motor is connected to a spindel, the goal is to detect ...
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### Co-variate contribution to model accuracy in multi-variate analysis

I have implemented a multivariate analysis in R as such: lm1<-lm(Y ~ A + B + C + D + E, data=data, weights = 1/Uncert) I found that the variable A contributes ...
7 views

### Applying paired t-test to compare averages

So I did an experiment for 1 month where I investigated the change of pH of 3 different types of milk in the refrigerator and room temperature. I d now like to compare the results of each type of milk ...
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Our experimental setting is a four-period crossover design: the table below indicates typical types of experimental data. ...
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### Learning curves - Why does the training accuracy start so high, then suddenly drop?

I implemented a model in which I use Logistic Regression as classifier and I wanted to plot the learning curves for both training and test sets to decide what to do next in order to improve my model. ...
6 views

### How to parallel SGD procedure?

I am doing some machine learning works with SGD to optimization the score function. I found that in each epoch, the task of each mini-batch is independent . We can save the grad of the parameter in ...
1k views

### In layman's terms what is the difference between a model and a distribution?

The answers (definitions) defined on Wikipedia are arguably a bit cryptic to those unfamiliar with higher mathematics/statistics. I am a high school student very interested in this field as a hobby ...
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### How to compensate for explanatory variables for a target variable? [on hold]

I have a few variables that explain for a big part a target variable, however I am interested in the part that is not explained by these variables so I want to normalize my data to these. I do not ...
18 views

### Post-hoc for 2x2 mixed design ANOVA using SPSS with two dependent variables

I am analyzing an experiment run with 162 participants using a 2×2 mixed design ANOVA. The experiment has two independent variable with two levels each, and two dependent variables. I need to know ...
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### Very general question about linear smoothers [on hold]

So the theory regarding local polynomial regression, splines, RKHSs tends to talk exclusively about 'linear smoothers'. But if we use the values of dependent variables to determine, say, bandwidths in ...
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Dependent variable is dichotomous D (0,1) and Independent variables are A (0,1) and B (0,1) and the confounder variables are age and sex. I want to calculate additive interaction, my question is: How ...
17 views

### Normality testing on subsets or whole data?

I have data for a continuous dependent variable that I'd like to test for normality. It is a time variable that measures the time of occurrence of an event within 30 seconds. If no event occurs within ...
68 views

### Computing conditioned probability of $X$ by $U=\min(X,Y)$

Let $X$ and $Y$ be independent random variables with $P(X\leq x)=F_x(x)$ and $P(Y\leq y)=F_y(y)$. Let $U=\min(X,Y)$. I know that $F_u(u)=1-(1-F_x(u)(1-F_y(u))).$ By definition: \$P(X \leq x |U=u)= ...
20 views

### Statistical significance testing over population

I have two data sets of 65 data points. I want to test the significance of the difference in distribution between them by Kruskal-Wallis test. But the data sets are not samples, they are the ...
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### How can one quantify the variable importance dilution effect in random forests (and similar statistical learning methods)?

In Applied Predictive Modelling (Kuhn, Johnson, 2013, p 202), the authors refer to a dilution effect whereby compared to a single tree or a classical regression technique, the difference in importance ...
5 views

### How to read multiple excel marco enabled files in r [on hold]

I'm very new to r. I'm trying to read 500 odd marcos enabled files in r but i'm getting error as "Error: Skipped over all data". Below code as been used to run the program. files <- ...
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### K-fold cross validation error in CausalImpact

I want to know how to get the prediction error in CausalImpact()function of CausalImpact R package. I am looking for something like 10 fold cross validation error?