Questions tagged [sample-size]
This tag is ambiguous. Use it when the question is about sample size and NONE of the following are more appropriate: [small-sample], [large-data], [statistical-power], [underdetermined], or [unbalanced-classes].
2,025 questions
5
votes
3
answers
220
views
Why does the p-value increase when I add more observations to my t-test?
I am comparing the means of two groups using an independent two-sample t-test in R. Initially, I had the following samples:
Group A: n = 15, mean = 52.3, sd = 4.8
Group B: n = 15, mean = 48.1, sd = 5....
- 51
5
votes
2
answers
89
views
Power of t-test with unequal sample sizes: GPower and MESS::power_t_test do not converge?
I've created two item sets with 24 items each, that I expect to differ along my outcome variable. To test this assumption before using the items in future studies, I'm planning to recruit human ...
- 53
3
votes
2
answers
156
views
Why doesn't the standard error depend on the number of samples taken?
I don't understand why the standard error of the mean does not depend on the number of samples of the mean that you take. To clarify, let's use a simplified version of the example in this answer. Two ...
1
vote
0
answers
110
views
Bias in standard error of regression slope with not-independent data and effective sample size
Consider a sample of $N/2$ pairs of individuals. Each pair belongs to a group $j$.
For each individual $i$ from the $N$ sample, I measure two variables ($y_{i}$ and $x_{i}$) and the average per group $...
- 267
7
votes
1
answer
195
views
Doubling your accuracy - extension
Frederick Mosteller's 50 Challenging Problems in Probability has a nice question I have not seen before, and I was wondering whether it could be extended.
49. Doubling your accuracy
An unbiased ...
- 45.4k
3
votes
1
answer
133
views
Sample size for multilevel exploratory factor analysis
I have a dataset of n=90 participants with ~20 variables for two conditions, with each variable having 4 data points (not statistically independent) for each condition. I am thinking about conducting ...
- 33
5
votes
1
answer
387
views
How many samples do I need to decide if there is a tie?
There are some 1,000,000 voters who vote for one of two candidates, A or B. I would like to decide if the election outcome would be a tie (that is, 500,000 vote for A and 500,000 vote for B). I poll ...
- 1,091
0
votes
0
answers
51
views
Naïve sample size calculation of non inferiority mixed model
First of all, thank you for this wonderful forum! I’m a physician with some statistics background but not a professional statistician. We plan an academic non-inferiority retrospective study with a ...
- 31
6
votes
2
answers
162
views
Are there rules of thumb for the sample size required when using a categorical predictor in linear regression?
I’ve had a reviewer suggest that I use ethnicity as a covariate in a linear regression. Some ethnic groups in the sample are small enough that I am a little worried that I will overfit if I do this.
...
- 1,091
3
votes
1
answer
93
views
Sample size for (average) bioequivalence in R
The aim id to calculate the sample size for average bioequivalence trial.
I would like to replicate the below example from "Sample Size Calculations in Clinical Research" by Chow and Shao (...
- 131
1
vote
0
answers
68
views
How can I shorten an A/B test on a binary registration metric when CUPED isn’t possible (new users only)?
Context
────────
• Metric: registration_success (binary 0/1, first-time users only)
• Baseline conversion rate: 15 %
• Target lift (MDE): +20 % relative (18 % vs 15 %)
• Power / α: 80 %, two-sided 5 %
...
6
votes
2
answers
315
views
How to properly apply an unpaired t-test in time-to-event situation vs. logrank test?
I'm calculating the sample size required in a study to determine whether a company's technology can identify delirium (a health event) more quickly than the method currently applied by the hospital I ...
- 265
1
vote
0
answers
52
views
Determine sample size based on a pilot to estimate the variability of ratios within a given level [closed]
After thinking back and forth for a long time, I just can't get any further with a problem. Basically, the question is how representative a number of samples is for a population. The word “...
- 11
0
votes
1
answer
110
views
Test the median of groups with differing sample sizes [closed]
I have a dataset that contains a set of values corresponding to independent groups. I want to to the median for each independent group. The central issue is the number of samples varies for each group....
1
vote
1
answer
201
views
How to calculate effect of sample size on false positive rate? [duplicate]
A placebo-controlled study (with sample size of 500) found that new drug reduces mortality from 10% to 7% with P=0.04.
Ideal sample size for such a difference (keeping 80% power and alpha of 0.05) is ...
- 10.4k
1
vote
0
answers
56
views
Determination of minimum sample size for a mixed model design with multiple observations per individual
I'd like to estimate a sample size for a study that estimates the interactions of groups and treatments, using a mixed model with one continuous response variable and two interacting predictors: group ...
- 590
12
votes
4
answers
717
views
How should introductory statistics material explain sample size estimation for means in the case of unknown population variance?
This is my first question here and I'm unfamiliar with statistics; I made an effort to search the site for duplicates, and there are related questions, but they don't quite address my question.
I'm ...
- 263
1
vote
1
answer
225
views
Chi-square power analysis
Thank you so much for your answers. Based on the responses and my lack of knowledge, I need to reword my question. Let's say I choose two categorical variables from my survey (ex., race with eight ...
- 31
1
vote
0
answers
44
views
Does the Overall Margin of Error Decrease When Analyzing a Stratified Sample as a Whole? [closed]
In stratified sampling, if each stratum is designed with a fixed margin of error (MOE)—for example, 3% per stratum—does the overall margin of error for the combined sample necessarily decrease when ...
- 11
0
votes
1
answer
130
views
Sample Size Calculation in Time-to-Event Analysis with Hazard Ratio as non-inferiority Endpoint
I'm performing a retrospective analysis on a dataset of 200 patients, who underwent either treatment A or B and where followed with regard to relapse and death. I've performed a survival analysis with ...
- 1
2
votes
1
answer
152
views
Determine sample size for validating success probability of Bernoulli process
Given a process producing a product with some constant defect rate $d$, I want to estimate the minimum sample size $n$ to confirm with a probability greater than or equal to $\alpha$ that the defect ...
- 23
0
votes
0
answers
45
views
How to measure the statistical significance of a change between two data vectors
Let's say I have 2 datasets of survey responses to 4 different questions. 1 through 7 is a numerical category from bad (1) to good (7). I want to compare how the distribution of responses changes ...
0
votes
0
answers
63
views
Can I use rarefaction analysis to estimate the minimum sample size needed to capture sample variance
In ecology, rarefaction analysis can be used to estimate the minimum sample size needed to discover all the species in a population. I was wondering whether this can be used to estimate the minimum ...
- 1
0
votes
2
answers
161
views
Using calc to find sample size in emmeans call for quasibinomial yields strange results [closed]
I've run a glm with quasibinomial family in an experimental study with a factor with 4 levels, 2 covariates and a binomially distributed response (the sum of 10 correct/wrong responses):
...
4
votes
2
answers
136
views
Logistic regression modeling of molecule conversion
A recent question addressed a regression where a chemical was treated with a mixture having a particular concentration, to see the proportion of the chemical that converted to a new substance.
The ...
- 72.8k