Tagged Questions

A test (typically of distribution, independence, or goodness of fit) or a family of distributions related to such a test.

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5 views

dependent and independent categorical variable across eight trials

Study: significantly selected color for a particular letter. My sample size is 30 and the study is within subject. Independent variable -> letters (total 8)... Dependent variable -> colors ( total ...
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9 views

The chi-square statistics reported above are based on only 2 of 51 units that had sufficient data for computation

So, we are doing a project for HLM class and we realized that for our final estimation for variance components and reliability estimates have this little note under the table. "The chi-square ...
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1answer
54 views

In a two-way ANOVA, how can the F-statistic for one factor have a central distribution if the null is false for the other factor?

Consider the two factor additive ANOVA model $$\begin{align} X_{ij} &=\mu_{ij}+e_{ij} \\ \mu_{ij}&=\mu+\alpha_i+\beta_j \end{align}$$ where as usual $\sum_{i=1}^a \alpha_i=0$ and ...
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15 views

Distribution of Standard Deviation of 2 Variable Linear Regression

Assuming we have a fit: $\hat Y= \alpha + \beta (X-\bar X)$ Such that: $Y_i=\alpha+\beta(X_i-\bar X)+\varepsilon$ The standard deviation of $\varepsilon$ is $\sigma$. Estimated in an unbiased way ...
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0answers
23 views

How do I convert Cramer's V to Cohen's d?

Say I have a chi-squared test that compares 3 different groups: $\chi^2_2 = 9.81$, $p=.012$, Cramer's $V=.33$ How would I go about converting this to a $d$-statistic? Is the proper approach in ...
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1answer
21 views

Chi-squared two sample test for unbinned discrete data

I am wandering through the net but I cannot get a precise description of how to solve this simple task. Two sets of datas ...
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0answers
15 views

Statistical Treatment in Yes/No/Maybe questionnaire

I'm currently in the midst of a research about wired LAN and WLAN for my english subject. My respondents would be 15 household users and 15 internet cafe owners. My reason for my research is to know ...
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1answer
76 views

Is there any correlation or causation here?

I have the following data, where 2 properties (P1 and P2) can be either True or False ...
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21 views

How to perform Friedman's test with covariates

I have 500 participants who each completed 30 trials. In each trial they need to choose the correct image out of three (a three-alternative forced-choice task). Of these thirty trials, 10 trials ...
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1answer
44 views

Weird pdf of a quadratic function of a N(0,1) variable: miscoding or big rounding error?

I would like to calculate the pdf of a random variable y defined by : y=c+b*x+a*x^2 The pdf is a non-central chi-squared distribution. For a>0, it should be equal ...
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31 views

What is the distribution of the difference between two Gamma's? [duplicate]

Suppose $X$ is $\text{Gamma} \sim (2,.5)$ and $Y$ is $\text{Gamma} \sim (2,.5)$ and $X$ and $Y$ are independent. Let $Z = 1/8(X-Y)$ what is the distribution of $Z$? I know $X+Y \sim (2+2,.5)$ what if ...
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43 views

Significance testing of categorical variables - is chi squared as good as it gets?

I am testing categorical variables for significant relationships, 5 age groups and 3 answer options (yes/no/don't know). Is there a test which will specifically tell me if e.g. age group 1 is ...
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20 views

Does N-1 correction for Pearson's Chi-Square apply to r x c tables generally?

Campbell (2007) recommended what he called the "N-1" correction for chi-square tests performed on two-by-two contingency tables. He described the correction as: "the K. Pearson chi-squared test ...
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1answer
16 views

What are the alternatives of a chi square test in testing for changes in categorial data?

I have done a survey trying to understand the waste disposal habits of people. One question is "What proportion of waste paper do you recycle". Another question is "Given a new local policy is ...
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1answer
50 views

Why can't the chi squared test be calculated with a row of zeros?

I have some trouble to calculate chi squared statistic with R. My data and code are: ...
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1answer
66 views

weighing the maximum likelihood

I would like to define a log-likelihood (starting with a gaussian distribution) for an observed value of a quantity ($x_i$), compared to the measured value based on a given model ($\hat{x_i}$) and ...
3
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1answer
69 views

Interpreting results of chi-squared

Situation: A/B test of a single website change on a landing page. Alternating visitors to the landing page are shown a variation. The goal is to convert more visitors into customers. With data that ...
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1answer
87 views

Why is the sampling distribution of variance a chi-squared distribution?

The statement The sampling distribution of the sample variance is a chi-squared distribution with degree of freedom equals to $n-1$, where $n$ is the sample size (given that the random variable of ...
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20 views

sample size to estimate variance

I am trying to follow a thread Calculating required sample size, precision of variance estimate? and am facing difficulty understanding a step in the answer, specifically the step given below $ (n-1) ...
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0answers
25 views

Determining Appropriate Test: two categorical groups with a goal (split test?) (Newb)

I've spent several hours online researching an appropriate means of using statistics to determine whether or not variation test results are meaningful, or just chance. If the testing took the format ...
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1answer
56 views

Given a chi-squared distribution, find $\Pr(\mu-2\sigma \leq Y \leq \mu + 2\sigma)$

Given a chi-squared distribution of df = 8, which R command do I use in order to find $\Pr(\mu-2\sigma \leq Y \leq \mu + 2\sigma)$? That is, the probability that $Y$ lies within 2 standard deviations ...
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2answers
52 views

Alternative for Fisher's exact test for count data in table bigger than 2x2

I have count data on different languages from comparable corpora. It looks something like this, where the counts give the number of clauses with that particular word order attested in each language ...
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1answer
29 views

Three proportions testing null hypothesis

I have the following question. In a random sample of 250 people with low incomes, 155 are in favour of a new piece of legislation, while in random samples of 200 people with average incomes and 150 ...
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0answers
26 views

Chi square test with replicates

Is there anyway to do chi square (or any other ratio rest ) with replicates. For example, my data have measures of different time points, each time points has 4 replicates. The measures are discrete ...
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0answers
18 views

A/B testing zero inflated data

I am trying to conduct an A/B(/C) test to compare the performance of 3 different website pages but I'm facing issues regarding zero inflated data. I have data for each page regarding ...
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0answers
12 views

which test for means of coded, categorical discussion forum posts?

I'm trying to wrap my head around this problem, how to state it formally for analysis (what kind of study is it) and which test(s) to run: I am comparing the content of 2 discussion forums (the study ...
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0answers
14 views

Friedman's test help in R

I'm trying to figure out Friedman's test in R and am confused by some of the output. For example, consider two groups where the ranks are reversed. Thus Group 1 goes from 1:40, then group 2 goes from ...
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0answers
21 views

What to use when chi-square independence assumption is violated

I'm trying to describe the characteristics of the sexual partners of each participant. There are multiple partners per participant. All of the variables in my analysis are categorical, so originally I ...
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0answers
45 views

Which statistical test for women height?

Suppose women may have Blue or Red eyes. We make a first cheap research on a 100 women checking just one eye of each woman. So after the research we have results: At least one eye Blue have avg ...
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1answer
28 views

Ways to test bar charts with few bars to see if they come from the same distribution?

I have survey data with ordinal/categorical data. Most of the time the answers to question are Yes/No. I want to compare the bar charts (normalized) of yes/no from participants who gave a particular ...
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0answers
10 views

Generalized minimum chi-square estimators?

I need to implement the generalized minimum chi-square estimators (alternative to L-moments method and maximum likelihood estimate (MLE)) for estimate the parameters of the gamma distribution. My ...
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1answer
42 views

Non-zero mean and finite-variance Gaussian Squared R.V has Non-central Chi squared distribution, but how?

If $$X \sim \mathcal{N}(\mu,\sigma)$$ then $$X^2 \sim \frac{e^{-\frac{\left(\mu +\sqrt{x}\right)^2}{2 \sigma ^2}} \left(e^{\frac{2 \mu \sqrt{x}}{\sigma ^2}}+1\right)}{2 \sqrt{2 \pi } \sigma ...
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0answers
32 views

Difference in Chi-square calculated by anova from cph and coxph

Is there a difference between Chi-square (from coxph -> anova) and Wald Chi-square (from cph ...
2
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1answer
32 views

Testing if a interval scaled variable A and a nominally scaled variable B are independet when A is not normally distributed

We have a variable A which denotes a percentage between 0 and 1. The variable is not normally distributed but has a very left skewed distribution. About 5% of the observations are zero, most ...
2
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1answer
55 views

Relationship between gamma and chi-squared distribution

If $$Y=\sum_{i=1}^{N}X_i^2$$ where $X_i \sim \mathcal{N}(0,\sigma^2)$. i-e all $X_i$ are i.i.d normal random variables of zero mean with same variances. then $$Y \sim Gamma(\frac{N}{2},2\sigma^2).$$ ...
2
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1answer
31 views

Wald test in logistic regression and its relationship to Z-statistic

If I have Z-statistic values in regression analysis, how can I convert them to Wald statistcs? Can Wald value be negative?
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0answers
40 views

Parameter distribution from profile likelihood

This question is regarding profile likelihood to obtain CI of parameters. There is a published parameter values that best fits (using minimum chi square)the data for some mathematical model say ...
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0answers
9 views

Is there a BIC or AIC formula for correcting a G-statistic?

I am using the G-test (http://en.wikipedia.org/wiki/G-test) for scoring models with different numbers of parameters in a model comparison problem. Is there a BIC or AIC formula to correct a ...
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1answer
63 views

If $\frac{(2n-1)s^2}{\sigma^2} \overset{}{\sim} \chi^2_{2n-1}$, can I take the variance of both sides to get an equality relation?

I currently have a standard result regarding variances and it looks like: $\frac{(2n-1)s^2}{\sigma^2} \overset{}{\sim} \chi^2_{2n-1}$ that is, it is approximately a chi-squared distribution with ...
3
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1answer
55 views

Hypothesis testing based on Likert type data

I know this site is full of similar questions, but either their answers do not apply, or I'm missing something. I have data from a questionnaire. Responses are in the form of Likert items, some of ...
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0answers
46 views

Testing uniformity of data

I need to test if a vector of observed values are uniform distribution. Lets assume: This values are not a sample, but my entire universe. I have a dataset of 12000 observations, where most of the ...
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1answer
16 views

Confidence interval from summaries in JMP

If i only have mean, std dev. and number of observations is it then possible to generate af 95% confidence interval or a Chi squared test in JMP using only these summaries as input?
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26 views

A/B testing on non-stationary populations

I am running A/B tests on a website. The daily engagement level of the users varies wildly, with a strong weekly seasonality. (Basically, users who are willing to use the software on Sundays are more ...
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0answers
17 views

One model or 178 models?

I am doing a school project, where I am modeling next quarter's stock price using the information about the stock in the current quarter. The main goal is to see if we can find any statistically ...
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0answers
15 views

Error type I for $X_i \sim Exp(\theta)$

Let $ X_i$ be i.i.d $Exp(\theta)$ for i=1,...,4.We want to test $H_0: \theta =6$ versus $ H_1: \theta = 2$. Consider the following test: $$\text{Test: Rejects H_o} \iff \frac{X_1 + X_2}{2}>4.5$$ ...
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1answer
113 views

How to assess the incremental additive information of a new predictor in a Cox model using R?

I want to check whether the addition of the new predictor x3 improves the predictive information of a Cox model significantly or not. So far I have: ...
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1answer
161 views

3x3 contingency table: what to use instead of chi-squared test?

I have questionnaire data from subjects divided into 3 groups, G1, G2 and G3. Subjects had to answer a question, and they had the options A1, A2 or A3 to choose from. The correct answer depended on ...
4
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1answer
201 views

Using brute force to get exact p-value instead of Chi-Squared Test of Independence

Background I have the following contingency table ...
2
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1answer
16 views

Is it OK to remove columns with low numbers in before running a chi-squared test?

I'm looking at significant differences for conversion by browser using a chi-squared test. My table looks like this: ...
3
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1answer
280 views

Why are these two random variables identically distributed?

Let $(X_1, X_2, \ldots, X_i, \ldots, X_k)$ be $k$ independent, normally distributed random variables with means $\mu_i$ and variances $1$. Then the random variable $$ \sum_{i=1}^k X_i^2$$ is ...