# Questions tagged [two-tailed-test]

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### How to identify a one vs. two-sided test (power analysis on proportions in R)

I have an oddly worded assignment for a power analysis on (paired) proportion data and I'm not sure if it matches the description of a one- or two-sided test. More specifically, I need to "see if ...
• 1,609
343 views

### Why is it the convention to take equal tails in a two-tailed test with a statistic following a symmetric distribution?

Is there a particular reason for conventionally dividing the tails equally in a two-tailed test? Consider an $\alpha$ level test with a statistic following standard normal distribution. Then, why do ...
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1 vote
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### Power analysis using bootstrap -- calculate power

I wish to conduct a power analysis using the bootstrap method to find the difference in means of two groups. I wonder how we can calculate the "power" if we do not know in our data, the null ...
• 11
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### How to calculate the sample size for a 2-sided t test?

I want to calculate the sample size $n$ for a two-sided t-test with the following values: alpha = 0.05 power = 0.8 effect size = 0.8 This is the code I tried in Python: ...
1 vote
85 views

### Doubt in calculation of critical region in two-tailed test

Consider the following question:- A tetrahedral die is manufactured with numbers 1, 2, 3 and 4 on its faces. The manufacturer claims that the die is fair. All dice are tested by rolling 30 times and ...
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### Practical (not theoretical) examples of where a 1 sided test would be valid?

I know that it is generally accepted that the two-sided test is the "Gold Standard". However, I just wanted to see if there are real life, practical applications of the one-sided test in the ...
• 991
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### Which degrees of freedom estimate to use for two-tailed t-test?

I have two samples: Sample A = businesses that have not received a grant Sample B = businesses that have received a grant Ua = population mean of survival rate for businesses in A Ub = population mean ...
• 1
41 views

### do you need to specify the direction of b for a moderated regression

I conducted a moderated regression, but didn't specify the direction of moderation by M. that is I didnt specify whether the relationship between X and Y would be greater at lower or higher levels of ...
110 views

### Does the one-tailed vs two-tailed argument apply in GLMs (i.e. Wald test) in the same way it would in a Student’s t-test?

I have constructed a gamma glm modelling hormone concentration with three predictors: treatment (treatment or control), sex (male or female) and site (thyroid, parathyroid). The work is mostly ...
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### How to interpret the niche overlap index (sensu Piyanka, Gotelli) 1-tail and 2-tail 95% CI?

I am trying to make sure I understand how to interpret Piyanga's niche overlap index and it's simulations in EcoSimR In short, if index is 0 (no overlap) and 1(complete overlap). I calculated temporal ...
• 603
1 vote
99 views

### Two-tailed z test for normal population mean

I am told that the mean of a sample follows a $N(\mu,\sigma^2/n)$ distribution if the sample is drawn from a $N(\mu,\sigma^2)$ distribution. A random sample of 9 observations has a mean of 53, the ...
• 13
1 vote
35 views

### Two-tailed hypothesis testing with different probability tails

I've been thinking about statistics recently and was looking over my university notes on the course. Specifically, about two-tailed tests, I was wondering whether it was possible to have the tail ...
• 11
1 vote
45 views

### How to calculate/interpret P-value in one versus two-tailed tests?

I am conducting an ordinal logistic regression and my alternative hypothesis is one-directional (I predict that my independent variable positively affects my dependent variable) and my null hypothesis ...
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