# Questions tagged [t-confidence-interval]

Confidence intervals for the difference of two population means, or the mean of a single population (or even parameter estimates) based on Student's t distribution.

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### How to calculate and plot a confidence interval for a bivariate normal distribution?

I have a two-dimensional normal distribution (with correlations). I do not have data points, but only the 2D mean and the covariance matrix. I want to draw the 68, 95 and 99% confidence intervals ...
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### Calculation of confidence intervals in linear regression model - normal or student?

I am working with a pretty simple linear regression model, in which I was asked to work with confidence intervals instead of p-values (classic) The thing is I was trying two approaches to get ...
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### Relationship between two independent confidence intervals and the confidence intervals for these two sample (mean, standard deviation, n) [duplicate]

I'm trying to learn about when there is a 'statistically significant difference' and the size of the effect. Imagine that we have a new medicine, and there is a Randomized Controlled Trial (RCT). The ...
98 views

### Confidence interval for the ratio

I have a problem that each customer gives us a revenue and a cost, one of the indicators of the company is the: $\frac{\sum Costs}{\sum Revenue}$ To estimate the confidence interval for this parameter ...
13 views

### Corrected standars deviation for confidence intervals [duplicate]

I have a multilinear regression model with 4 parameters and 164 observations. I want to determine the confidence intervals for each coefficient of the multilinear regression. I have the covariance ...
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### Why doesn't R output for a paired t-test match the formula for a confidence interval in the t-distribution?

My understanding is that the formula for a confidence interval when using a t-test is as follows: $\bar x \pm t_{n-1,\alpha / 2} \frac{S_d}{\sqrt{n}}$ where $S_d$ is the standard deviation of the data....
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### Why does the question state standard deviation is unknown, when it is written in the question? See problem Below

The question "The dean randomly selected 25 students who took the calculus final exam and looked at their scores on it. In this sample the mean was 85.7 and the standard deviation was 4.2. The ...
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### Confidence interval for standard deviation ($\sigma$)

I‘m trying to find 95% confidence interval for $\sigma$ from a given sample. The sample is: $$n=6 \\40000, 200663, 142690, 48560, 40000, 242628$$ (we know that we’re dealing with normal distribution)...
1 vote
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### How should I decide how many decimal places to use in a confidence interval?

My T table look up is to 3 decimal places ( or less is I am estimating for n=39 say) Yet my margin of error can be calculated to as many decimal places as I choose. How should I decide how many ...
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### Confusion about how to look up t value for margin of error in confidence intervals

I have been given the formula for a confidence interval on a gaussian distribution with unknown variance as $\bar{x} \pm t_{\frac{\alpha}{2},n-1} \frac{S}{\sqrt{n}}$ And I am wondering which column ...
• 793
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### Confidence interval for samples with frequencies

I have a total population size of $N$ (known). From the unique elements of the pool I draw samples $s_i, i=1 \ldots m$ without replacement. I also know that each sample $s_i$ appears $k_i$ times in ...
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1 vote
### What place does $s = \sqrt{\frac{(n_1 - 1)s_1^2 +(n_2 - 1)s_2^2 }{n_1 + n_2 - 2}}$ have in confidence intervals?
I was recently constructing a confidence interval for the difference in population means of two samples ($\mu_A$, $\mu_B$). Both samples were taken from different populations (e.g. $A$ and $B$). It ...