This tag is very ambiguous. Use it when the question is about sample size & the following are NOT more appropriate: [small-sample], [large-data], [power-analysis], [power], or [underdetermined].

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18 views

Sample size calculation, linear regression

I have just had my viva and my sample size calculation was criticised as it was based on r2. I was told to base the sample size on the minimal magnitude of association. My outcome variable is HbA1c, a ...
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0answers
7 views

Sample Sizes Based on Cost Efficiency

I am planning a biology experiment that is testing the predictors of biological markers.These predictors are: Gender.(Binary) Smoking status.(Binary) Alcohol consumption.(Binary) Hiv infection ...
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0answers
24 views

Sample Size for Comparing two Measuring Tools

Let's say I have two devices that measure the same thing: the thickness of an object. Knowing that device 2 is more accurate and precise, I wish to see how accurate device 1 (how close do the readings ...
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2answers
110 views

Adjustable sample size in clinical trial

Most clinical trials I see have a fixed sample size. In some cases they have prior data that allows estimating the effect size and the variance or distribution of values, and calculate the sample ...
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0answers
9 views

Correlation computing time series data of unequal sample size

I am working on a computing a correlation between two variables X and Y. Both are time series and were recorded during the same period. 6/25/15. However X was recorded much more often than Y. ...
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0answers
36 views

Why sample sizes are often powers of two?

A layman's question: why are powers of two a commonly selected sample size? What are the practical reasons for setting them as such?
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0answers
32 views

Cluster Sampling involving Design Effect

A survey of residents is performed using cluster sampling. The design effect is 3.00. From the survey, the estimated proportion of people who are happy with their insurance company is 0.42 with a ...
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0answers
8 views

x and y standard deviation estimates in linear regression power analysis

I want to run a power analysis on linear regression against the null that the slope is equal to zero. Specifically I am trying to estimate what sample size I will need to obtain a specific power level ...
4
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1answer
140 views

how big to make k for cross validation

Is there a limit to how big you should make K for k-fold cross validation? I understand as K gets bigger performing the CV will take longer, but aside from that, is there any reason not to make K = n? ...
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3answers
3k views

What can we say about population mean from a sample size of 1?

I am wondering what we can say, if anything, about the population mean, $\mu$ when all I have is one measurement, $y_1$ (sample size of 1). Obviously, we'd love to have more measurements, but we ...
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0answers
19 views

Sample size for a small proportion

I'm calculating the required sample size for the following RCT design: the baseline proportion is 3%, and I want to be able to detect a difference of 1ppt with 80% power. If I use the sample size ...
2
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2answers
41 views

Relation between power and sample size in a Binomial Test?

$\beta$ (also called sensitivity or power) is a function of the sample size. It totally makes sense to me when we're performing a regression for example. The intuition is not that clear when we ...
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1answer
32 views

SEM - sample size and power

Muthén & Muthén offer a MPLUS based syntax for calculating sample size and power on SEM, using a Monte Carlo simulation. https://www.statmodel.com/download/FinalSEMsingle.pdf Is there any ...
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0answers
16 views

What are some major theories on picking the right number for the sample window size in time series analysis?

for example the number of samples to run the moving average, or the number of samples for sequential hypothesis testing. Or if there is a control scheme going on what is the best time window for an ...
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0answers
24 views

Use a model to reduce sample size?

I have a consultant that is proposing that he can reduce my sample size by using a model that is built off of previous samples. My first response was "NEVER EVER EVER EVER DO THIS". However, after ...
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1answer
21 views

sample size for metric survey data

I currently read this paper http://www.opalco.com/wp-content/uploads/2014/10/Reading-Sample-Size.pdf and try to understand sample size calculation. This paper presents Cochran's formular: ...
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0answers
17 views

Expected Euclidean distance between normal prior and posterior as sample size changes

Suppose the prior for some random variable $x$ is normal with mean $\mu$ and variance $v$. Denote the prior density by $f(x|\mu,v)$. Given normal likelihood with known variance $v$, the posterior for ...
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0answers
15 views

Longer panel has fewer obs?

I am using Stata 13 to analyze a panel. Recently, I received an update to the panel with a few more years. I ran the exact same probit regression including the longer time horizon. All used variables ...
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0answers
21 views

Incidence rate in a cohort with small sample size

I am dealing with the following problem: I have a small cohort of people with a specific disease (n=300) and studying the incidence of a related disease (which is kind of rare and normally occur only ...
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0answers
31 views

Sample size calculation for crossover design using dependent t-test - role of $\rho$?

I am trying to do a sample size calculation for a 2x2 crossover study. I have access to previous studies whereby I can get covariate adjusted estimates of the variability of the responses (from a ...
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1answer
22 views

Should the sample sizes be equal for non-parametric tests?

I randomized samples into two experiments and I ended up with about 190 samples in one group and 80 in the other. The distributions of the two samples are not normal and I want to use Wilcoxon test to ...
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0answers
19 views

Do I need to adjust the sample distribution to test significance?

The question in the title is probably not very clear, so let me explain better what my problem is. Suppose I have the following data from a survey: A categorical variable indicating the age of the ...
0
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1answer
51 views

Paired two one-sided t-tests (TOST) with unequal sample sizes

I have data from two populations (let's call them "before" and "after"), collected in a paired fashion. That is, I take a measurement under one set of conditions before, and then I can take multiple ...
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0answers
42 views

Correct Sample Size N in a Relative A/B Test with Binomial Variates

I randomly assign users to two distinct groups and track their return rate to the website (the return rate on each day for each group is simply $\frac{Number Of ReturningUsers}{TotalUsersOnDayZero}$). ...
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1answer
23 views

Influence of highly unequal sample sizes on statistical tests and data visualization

How would I go about comparing two populations (A and B) with unequal sample sizes. Sample size of A, SA: 10,000 Sample Size of B, SB: 2000 My goals are: To use data visualization tools to study ...
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3answers
207 views

Sample size calculation for correlation study

I am planning a study to assess the correlation of perceived stress in medical students and their academic performance. After a literature review, it appears that one previously done recent study has ...
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0answers
37 views

Skewed data, unequal n - advice?

This is the first time I have dealt with non-normal data (lucky me!), and I have come to a bit of a road block as to what tests to run. Experiment: Investigate whether false feedback affects ...
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1answer
37 views

How can I find out the needed sample size

I'm going to study if medical reconciliation diminishes the amount of inappropriate medications amongst elderly people in a small part of Sweden. I will count the number of inappropriate medications ...
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0answers
28 views

T-test formula when population standard deviation is known [duplicate]

I got this question from my mentor. Marks obtained by 10 MBA students in Statistics paper (out of 50) is given below. 20.5, 18.25, 10.23, 15.47, 35.62, 47.64, 12.30, 29.65, 38.5, 14.79. Test whether ...
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1answer
16 views

Sample size estimation for MANOVA

I am trying to run a replication of a study which used a factorial design (2x2) with three DVs (dependent variables) and subsequently ran three ANOVAs to test their hypotheses. Given that the DVs in ...
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0answers
57 views

How did they power this study? (One sample proportion test)

I was asked to perform a sample size calculation for a study with a single arm and a binary outcome. They have given me an assumed proportion, $p$, and need the upper 95% confidence interval to be ...
2
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1answer
55 views

I want to take a decision on two gaussian distributions, what approach can I take?

I observe a one dimensional random source, which could be any of two Gaussian distributions with a different set of parameters that do not change over time. They have a the same variance and a ...
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1answer
32 views

Two way ANCOVA with slight heteroscedasticity

I am about to perform a 2-way ANCOVA but I reject the null hypothesis in Levene's Test with a p-value of 0.023. See standard deviation and sample sizes below. I googled up and down and found people ...
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0answers
22 views

Manufacturing Process Validation - Sample size calculation

I am new to manufacturing process. Can someone help me to determine the sample size required to perform Manufacturing Process Validation? I know nothing about six sigma, so simple answers are highly ...
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0answers
31 views

Sample size selection discrete case

I have an algorithm that predicts either 1 or 0 , not prediction value like 0.25, or 0.58 or 0.92 or anything like that. I am wondering what is the formula for sample size selection during the ...
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0answers
38 views

t-test with unequal sample size, very large group and very small group [duplicate]

If I have data for 2 group with unequal sample size, first group $n_1=81$, second group $n_2=72000$. Can I still do a t-test for comparing the mean difference between these 2 groups?
2
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1answer
35 views

Problems due to analyzing variables from different levels at one single level

Please ease the following paragraph from the first chapter , Introduction to Multilevel Analysis , p.3 of the book: Historically , multilevel problems have led to analysis approaches that moved ...
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0answers
24 views

Computing Required Sample Size to Control Type II Probability

Let $X_1, \dots, X_n$ be a random sample from $\mathcal{N}(\mu_0,\sigma^2)$, $\mu_0$ known, $\sigma$ unknown. Consider $H_0:\sigma^2=\sigma_0$ vs $H_1:\sigma^2=\sigma_1^2$ where $\sigma_1 < ...
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0answers
11 views

Research Model for Two Samples

I am currently doing my undergraduate research, which entitled the relationship of board composition and financial performance in growth firms and mature firms. I need a help to find the best research ...
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2answers
64 views

What will be the t-value if my sample size increases to an infinity compare to z value?

I do not know where to check this. Any reference/help is much appreciated. If the sample size, n increases to an infinity then will the t-value be larger/smaller ...
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0answers
23 views

Have I interpreted the effect of a confounding variable correctly?

I'm interested in whether feeding rate differ between two species of birds, Species A and Species B. However, tide also affects their feeding rate, and so tide is a confounding variable. In the plot ...
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0answers
37 views

Power Analysis for Logistic Regression with one nominal variable

How do I estimate sample size or do power analysis for logistic regression with one nominal independent variable? Is there a way to do it with Stata?
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3answers
46 views

How many samples needed to approximate true mean?

If I have some arbitrary random variable with true mean $\mu$ how many samples from its distribution do I need to take such that the empirical mean $x$ approximates $\mu$ within an error of less than ...
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0answers
38 views

Rule of thumb for sample size for mixed-effects logistic regression analysis?

Is there a simple way of calculating the minimum number of participants (and/or items) needed for a mixed-effects logistic regression analysis? In particular, what should I do if I don't know what to ...
2
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1answer
52 views

Information criterion for selecting sample size when modeling tails

I want to model the left tail of an unknown distribution with a Generalized Pareto distribution. Somehow I have to select how much of the tail to model. I am wondering if it is possible to create an ...
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0answers
17 views

Comparing differences in pairs of ratings using a bootstrapping like approach

I'm pretty new to bootstrapping like approaches. So I do apologize for any inconvenience. I have two independent samples, snow (n=120) and nonsnow (n=608), consisting of pairs of ratings on a ...
0
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1answer
41 views

Mulitivariable regression?

For my research project on the effect of a specific kind of surgery on clinical outcome, I want to study the correlation between the improvement in clinical outcome scores (ie the difference between ...
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0answers
56 views

Incidence rate sample size

Hi am trying to reproduce the following computation from a paper, but cannot acheive it. Sample size calculation was based on the combined incidence rate of moderate and severe hypoglycemic events ...
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0answers
56 views

Relative size of p value at different sample sizes BUT same odds ratio

Will the relative size of the p-value increase or decrease with the increase of sample size? My guess is that it will decrease, however, would it be the same case if they both have the same odds ratio ...
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1answer
27 views

How are sample size and confidence related when calculating Sample mean?

Maybe I'm getting ahead of myself and I should just keep reading my textbook, but I'm getting confused about something. Let's say a friend gives me 10,000 integers that he claims are normally ...