Questions tagged [exact-test]
Statistical tests where the sampling distribution is necessarily exactly correct & not an approximation based on assumptions &/or large sample theory.
42
questions
0
votes
2answers
33 views
exact binomial test with power calculation that excludes the lower limit of a 95% CI
In a regulatory document I see the following statement and wonder how the sample size of 141 subjects is calculated:
A sample size of 141 subjects provides 80% power to exclude a response rate of 12% ...
0
votes
0answers
27 views
Which of the 3 given exact methods of calculating the confidence interval for median is better (correct)?
I want to calculate CI for the median in R. I found a number of packages and functions doing that and noticed something interesting. I think the problem can be generalized to any statistical software. ...
4
votes
2answers
57 views
Single sample t-test variance assumptions for non-normal data
So I understand that a key assumption behind the single sample t-test is that the sample mean is normally distributed. This is true when the data themselves are normally distributed, and it is ...
7
votes
2answers
184 views
Paired vs independent t-test for A/B test with underlying trends
There is a metric which has a natural cyclic pattern. We want to measure the effect on this metric through a A/B test.
Examples:
Metric is daily revenue of ice-cream trucks which is low during ...
0
votes
0answers
10 views
Fixed/unfixed maginals in case/control studies on pre-existing data?
I am performing analyses on a wide variety of existing datasets (taken from GEO) with case/control status. I want to do exact tests on a 2x2 contingency table and am unsure if I should use Barnard's ...
1
vote
1answer
67 views
Can exact tests compare groups from case-cohort studies?
I have reviewed several helpful threads most related to my question and many thanks to the authors. The first thread suggests odds ratio is valid for cohort studies, but risk ratios or hazard ratios ...
0
votes
1answer
13 views
Check if multiple percentage are significant
I have 3 measurements of a very skew distribution, depending on three different technique. In general, I can do thousands of test and the result is either "fail" or "success", being the "fail" far ...
3
votes
1answer
51 views
Exact distribution of number of transitions in a binary vector of length $n$
I am trying to derive an analytic solution for the exact distribution of the number of transitions in a binary vector of length $n$ conditional on the observed number of $1$'s and $0$'s and under the ...
3
votes
1answer
399 views
Confidence interval for quantiles: distribution-free, asymptotic and assuming a normal distribution
An acquaintance of mine has been using this wrong inference formula for years: given
a i.i.d. sample $\mathbf{X}={X_1,\dots,X_N}$ for a continuous RV $X$,
sample mean $\bar{X}=\frac{\sum X_i}{N}$ ...
3
votes
1answer
60 views
Examples for exact tests which are not permutation tests
Wikipedia states (without citation):
Sometimes permutation test is used as a synonym for exact test, but although all permutation tests are exact tests, not all exact tests are permutation tests.
...
1
vote
1answer
34 views
Number of all sample divisions in permutation test
I have a question with regard to the number of permutations in a
permutation test. Assume I want to do a two group independent t-test.
In the permutation variant of the t-test, I would repeatedly ...
1
vote
1answer
304 views
How does Normal approximation work when ties exist for Wilcoxon Signed rank test?
I ran wilcox.test() in R (outcome variable was a test score and the data was paired samples) and got a warning message saying that it cannot generate a p-value for tied values. I saw the R document ...
0
votes
0answers
45 views
How to perform an exact test of Chi-square for a single-dimension data in R?
I have a data frame like this:
> fr.t.r
A B C D E
Freq 13 3 0 0 0
and I would like to do a Chi-square test to find out if the ...
0
votes
1answer
884 views
How IBM SPSS calculates exact p value for Pearson Chi-Square statistic?
Usually, I use Fisher's exact test p value when the sample size is small for Pearson chi-square test. Then I realized that IBM SPSS reports exact p values for all the tests (i.e. Pearson Chi-Square, ...
0
votes
0answers
55 views
when an exact binomial confidence interval should be used?
Is exact binomial confidence interval only appropriate for extremely rare events or extremely frequent events? If so, what are the rule of thumb for the definitions of extremely rare (<0.01?) And ...
1
vote
1answer
268 views
Exact MCMC Logistic Regression Output
I am having trouble interpreting the output of an MCMC Logistic Regression run using R from the MCMCpack. Unfortunately I have had very little luck in finding sources on the web.
I am assuming that ...
1
vote
0answers
90 views
LRT and $\text{Uniform}(0, \theta)$
We have one observation of variable $X$ that is distributed uniformly on $[0, \theta]$. Null hypothesis is $H_0 \colon \theta = 1$ and alternative hypothesis is $H_1 \colon \theta = 2$.
What is the ...
6
votes
2answers
166 views
Drawing conclusions of several inferences with the same data in one study
In a sample size of 100, we identified the existence of two attributes A and B.
Our goal is to assess whether there is any ...
4
votes
1answer
2k views
1
vote
0answers
80 views
Barnard's exact tests - papers?
I am currently writing some essay for the university in which I should give a quick overview over exact methods for independence testing on contingency tables, after writing down the stuff for Fisher'...
1
vote
0answers
271 views
Boschloo's exact test
I have following data in R:
d1 <- matrix(c(24,2,63,11),2,2,
dimnames=list(X=c("present", "absent"),Y=c("present", "absent")))
I want to test ...
5
votes
1answer
830 views
z-test for one population proportion hypothesis with a small sample size
I have asked a "yes/no" question to a small group of people (n = 22). From the 22, 14 answered "yes" and 8 answered "no". I'd like to find out, with 90% confidence, if the majority of my population (> ...
0
votes
1answer
377 views
Sample size determination for comparing two independent samples with regards to several continuous variables
I am interested in calculating the required sample size to perform several statistical tests on the same sample.
More precisely, this is the situation:
There are two groups of individuals, A and B, ...
5
votes
0answers
151 views
Exact Null Distribution with Ties
I am interested in deriving exact null distributions for small-sample test statistics with non-trivial ties. Not fundamentally continuous variables that happen to have a few repeated values, but ...
3
votes
0answers
576 views
pre-post testing: paired nominal data with more than 2 categories
I have two groups of students who answered a question on the pre-survey about their savings behavior, i.e. choose one answer a/b/c/e/d/f: (a) Save the same amount each week, (b) Save varied amount ...
1
vote
1answer
165 views
how we do student T-Test?
In my data water is control and gibberellin is positive control. We want do find the activity of steviol against water and gibberellin. How we do student T-Test?. My data of height of plant in cm is ...
2
votes
0answers
165 views
Covariates in a case control study
I am doing a retrospective analysis on a study has has cases and controls. I am looking to see if there is an association with death, using exact logistic regression. I am confused on whether I need ...
3
votes
0answers
3k views
Threshold for and Variations of Exact logistic regression
According to this UCLA tutorial exact logistic regression (elrm::elrm in R) should be prefered to the logistic regression ...
2
votes
1answer
406 views
Exact multinomial goodness-of-fit test as a normality test
We have a practical real-life problem in an open source Linux related project. And I would like to hear an expert review/opinion about the way we are trying to solve this problem. It's been more than ...
5
votes
1answer
3k views
How do you know if your confidence interval is exact or approximate?
I would like to know the rules between the two, and know how you know the differences.
1
vote
1answer
1k views
What is the minimum sample size for an exact binomial test of goodness of fit (two-tailed)?
I am doing a two tailed exact binomial goodness of fit test, see, e.g., here. I am looking for something similar as for Chi-square tests, which, as a rule of thumb, require a frequency of 5 for each ...
4
votes
1answer
1k views
Exact test for m x n contingency table conditional (i.e. fixed by design) on one margin
I have a $m \times n$ contingency table (with $m, n > 2)$ . The experiment yields ~15% cells with expected frequencies lower 5 and also zero counts in the empirical data. The prerequisite for the ...
3
votes
0answers
70 views
Test of strict difference in independent binomial probabilities
Suppose $X,Y$ are two independent binomial random variables with parameters $n_1,p_1$ and $n_2,p_2$ respectively. Suppose one wanted to test the hypothesis $p_1>p_2$. Conditional on $X+Y=s$, ...
3
votes
1answer
431 views
Non-parametric, repeated measures two-sample test with small sample size
My data consists in two samples relative to the expression of a given gene, with 4 replications in both samples.
I am interested in testing whether the two samples come from the same population, ...
2
votes
0answers
180 views
Questions about non-standard test statistic for difference of two population proportions
Background
I'm considering the number of observed 'successes' $x_1$ and $x_2$ from $n_1$ and $n_2$ independent trials respectively. These counts can be considered realisations of random variables $...
9
votes
3answers
639 views
Test to distinguish periodic from almost periodic data
Suppose I have some unknown function $f$ with domain $ℝ$, which I know to fulfill some reasonable conditions like continuity. I know the exact values of $f$ (because the data comes from a simulation) ...
1
vote
2answers
210 views
An exact paired perm.test is returning a p-value of 0 for large sample sizes
I'm trying to find the p-value from an exact paired permutation test. For small samples it works fine:
...
4
votes
1answer
1k views
Proper analyses for 2x2 contingency tables
So I have multiple questions about the different types of analyses that can be used on a 2x2 contingency table and when different analyses should be used.
To open, I'll note that this stems from my ...
4
votes
2answers
1k views
Is the binomial sign test really the exact McNemar test?
I am calculating two different $p$ values for the McNemar test and what I believe is the corresponding exact test, even for combined counts larger than 25.
Take, for example the contingency table
<...
1
vote
0answers
40 views
exact test on proportion: confidence intervals vs p value [duplicate]
I have the following 2x2 table
NO YES
9690 5 LOW
26354 39 HIGH
I want to
plot the proportions and ...
0
votes
0answers
436 views
Exact p-value for any nonparametric test
After having found the R-package coin, I have a question.
For example, to get an exact p-value, I could use the function ...
1
vote
1answer
432 views
Exact probability and asymptotic approximation
From Wikipedia
A large amount of computing resources is required to compute exact probabilities for the Kruskal-Wallis test. Existing software only provides exact probabilities for sample sizes ...
