An inquiry into the quality of a statistical test by calculating the power - the probability of rejecting the null hypothesis given that it is false - under certain circumstances. Power analysis is often used when planning a study to determine the sample size required to achieve a nominal level of ...

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23 views

Sample size calculation - Pros and cons of using one-sided z-test over two-sample differences in means approach?

I'm calculating the sample size required for an experiment with continous outcome variable. I'm considering two ways to calculate the sample size. One is based on a differences in 2 means test. The ...
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0answers
21 views

Power analysis for AB testing— multiple variants

I'd like to do an experiment that is basically an A/B test with about 10 different conditions. A single trial results in either success or failure. The null hypothesis is that all of the conditions ...
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0answers
11 views

Determining the effect size using GPower

I have three ponds and would like to know how many random samples of algae I need to collect within each pond measuring 7 response variables. I would like to see how each pond responds to the 7 ...
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0answers
25 views

Using G*Power to determine the sample size for an repeated measures ANOVA

I am currently designing an experiment that I want to analyze using an RM ANOVA. Since some of the factors are confounded I need to do multiple ANOVAS. One analysis will be for 2x2 factors (within ...
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0answers
12 views

Cluster weights in PROC GLMPOWER

I am doing power analyses in SAS using PROC GLMPOWER to solve for a total sample size (N Total). I have clustered data (Ward method), to account for variability. There are 4 clusters of varying sample ...
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1answer
80 views

Computing the power of Fisher's exact test in R

Suppose that I have the following 3 x 3 contingency table: ...
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1answer
30 views

How to caculate power analysis in a descriptive study

Hi I'm currently doing a dissertation, its a descriptive quantitative study. The method of data collection is a questionnaire scaled by a 10 point Likert scale. To calculate the sample population ...
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39 views

Repeated measures or two-way ANOVA, and power analysis

A sample of patients will undergo two treatments. Every patient will receive both treatments.One treatment will on the left side and the other different treatment on the right side. Repeated ...
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17 views

Retrospective power analyis of lmer for sample size

I'm an MSc student doing an assignment where I am asked to analyze and write up a report on a dataset on environmental enrichment in zebra finches. Among other things we are being asked to do a ...
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1answer
53 views

Calculating sample size of a mixed ANOVA in R (2 between, 1 within variable)?

I'm searching for a built-in function in R for calculating the required sample size (given certain power, alpha,..) of a mixed ANOVA (2 between, 1 within variable, 2x2x2 design). Does this function ...
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0answers
41 views

Post-hoc power analysis of complex sample survey data

I am working with a complex sample survey data using Stata to determine the predictors of a given dependent variable. As part of my analysis result I want to report the post-hoc power for each ...
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1answer
60 views

How to calculate sample size for this study design?

I am trying to find out whether the number of participants I recruited (N=42) so far is sufficient for my study in which: there are two interfaces (say A and B). ALL students in the study will try the ...
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1answer
14 views

Prevalence estimates based on randomized sample of clinical data

This is probably one of the more straight forward questions on here but here it is: I want to use a random number generator to sample X number of charts to look for the # occurrences of Y event. So ...
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1answer
48 views

Power analyses of 5 populations of infection data (binomial data) [duplicate]

I am PhD Biologist. I have 5 populations of infected moth larvae (3 inbred, and 2 outbred). The infection in this case is spread vertically (from mother or father to offspring). Normally the virus is ...
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0answers
43 views

Power calculation for a coefficient in linear regression

Consider a simple linear regression of the form: $$ Y \sim \beta_0 + \beta_1 X + \beta_2 Z + \epsilon$$ I have questions regarding calculation of power for $\beta_1$. To calculate power, I approached ...
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1answer
25 views

Matching two power signals for similarity

Below are the images of two signals that i plotted. Both the signals are from fridge belonging to different houses. Visually looking at the plot i can tell that these plots belong to fridge as they ...
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0answers
26 views

Cross correlation of two power signals

I have two devices and their power usage data. I am trying to see how co related these two devices are. i.e If i use device 1 then how often i am using device 2. It will be helpful if anyone can ...
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2answers
89 views

Empirical rejection rate of a wrong null hypothesis -is it the “power of the test”?

I guess this is basic, but it forms part of the holes in my statistics education. What I know is that the power of a hypothesis test is not a fixed magnitude, but a function of various factors ...
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1answer
29 views

What kind of test is this?

I have a client that wants to test 3 pricing options to visitors of a website. All options are for the same product and service (no difference except pricing). Their current idea is to present all 3 ...
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0answers
25 views

Calculating n: Determining r

I have to calculate n for my research. I'm using a calculator (this one: http://www.cct.cuhk.edu.hk/stat/other/correlation.htm). α = 0.05 β = .2 r = ... I have trouble figuring out what r is. I get ...
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1answer
46 views

How to choose a Power and Alpha combination for a fixed sample size?

Let's say I have a sample size established with alpha=0.05 and power=0.8 (based on time constraint for study). The same sample size can be achieved with any of: ...
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1answer
53 views

Calculate required sample size with R with known power and ratio of n1 to n2

If I know that d=0.8, sig.level=0.05, power = 0.8, ...
1
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1answer
39 views

Power analysis for repeated measures design with ordinal response

I am designing a randomised pretest-posttest trial for which I'm trying to do a sample size calculation. My brain is about to explode from confusion, so I hope someone can help me. Just a little ...
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0answers
60 views

The a priori power of test for a simple effect within a 2x2 ANOVA

I need to know about the power of a simple effect that follows from a 2x2 ANOVA interaction. Let's call the factors in this design GROUP(Patient, Control) and MANIPULATION(Expectation, Random), ...
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2answers
146 views

Why is power analysis with logistic regression so liberal compared to chi squared?

I'm conducting a power analysis to derive the required sample size for a study - basically compared exposed / non-exposed with 30-day mortality as outcome. I'll check for crude mortality rates with ...
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1answer
61 views

Linear Model or Logistic Model: Can Someone Recommend a Book?

I have a huge data set that looks roughly like this: ...
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0answers
37 views

Unbalanced sample size: Bayesian vs. frequentist approach

I have a question concerning tests between a large control cohort and a smaller number of cases in a simple comparison. In particular I was wondering about the differences of baysian and frequntists ...
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171 views

How to calculate post-hoc power analysis for multiple regression models?

I have few questions that came up while I was trying to calculate post hoc power analysis for a regression model: I calculated post hoc power analysis for a regression model that produced a ...
2
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1answer
116 views

Power analysis from Bayesian point of view

I was reading an article on a power analysis and sample size calculations for a class of models that known as joint longitudianl-survival models. The paper derives a closed form formula for power and ...
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2answers
120 views

What does a post hoc power analysis say about the significance of the study results?

I orginially posted this over at AskMetafilter, and a commenter suggested I ask it here. I work for a dietary supplement company that also makes skin care products, and some of those skin care ...
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1answer
73 views

ROC/AUC Confidence Interval

For a single ROC curve (with relevant AUC score), how can you calculate the confidence interval? (The data used to generate this ROC/AUC is available) Given my relatively limited background in this ...
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1answer
53 views

Power analysis for binomial data when sample sizes are different

I'm running an A/B test where I want to compare two different layout of a button and want to see if one layout lead to a higher Click-Through Rate with a certain statistical power. I want to use a ...
5
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2answers
365 views

Can I do a t-test Power Analysis for Unequal Size Groups which Produces 2 Different Minimum n's?

It's usually straightforward to do a Power Analysis to compute the minimum sample size, especially in R which is my preferred ...
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0answers
40 views

Power Analysis for Text Mining

I have a population of 6 million text files with which I want to perform sentiment analysis (and text analysis more generally). I will need to manually hand code a subset of these texts into positive ...
2
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0answers
37 views

When do sample size calculations need to adjust for clustering?

I am aware that sample size calculations for cluster RCTs must adjust for clustered data. I would like to understand better if such adjustment might be necessary for other study designs. For instance, ...
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0answers
16 views

Determine minimum number of observations to be checked manually

I'm trying to classify transactions (say credit card transactions) as good or bad without looking at it manually. (The only way to figure out whether a transaction is good or bad is by manually ...
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51 views

How to do a power analysis for an unbalanced mixed effects ANOVA?

I need suggestions for how to calculate the $n$ required for 80% and 90% power for >30% change from baseline ($T_0$) at $T_1$ or $T_2$, drug vs. placebo, 2:1 ratio; 20% CV in test; factors: subject, ...
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0answers
61 views

Power estimates for an interaction in a 2X2 factorial design with a proportion outcome

I am trying to calculate the power that I will have to detect an interaction between 2 different interventions in a 2X2 factorial design. We aim to have about 850 participants in each of the four ...
7
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1answer
232 views

Sample size calculation for paired ordinal data

What formula should be used for sample size calculations for paired ordinal data? Imagine we have an intervention and we want to measure the effect based on before and after measurements of an ordered ...
0
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1answer
17 views

How many samples are needed for a paired trial with multiple tries?

I'm having problem understanding how big sample size is needed for a situation where there are pairs in the before/after groups but these have all multiple data points. Problem Pose a situation ...
2
votes
1answer
489 views

Sample size calculation for ROC/AUC analysis

As a background, I am not familiar with stats except on a basic level. I have been tasked with doing some analysis that is out of my comfort zone. I am trying to figure out how to compute necessary ...
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3answers
119 views

Large sample size for t-test

I am working on a physics experiment, and I ran 500 runs to calculate a parameter. I want to use the t-test to see if my mean from 500 runs matches the actual value. u0: mean is actual value u1: ...
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0answers
45 views

Questions about G*Power

Since I found an insignificant result, I performed a power calculation in G*Power. But I am not entirely sure if I input the right number in some fields. My design is a 2(between Ss) x 2(between Ss) ...
5
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0answers
133 views

Minimum sample size for a dichotomous outcome [closed]

I have two questions. I am running an experiment where I am interested in determining the sample size required for a certain CI (confidence interval) and error, where values range between $<1$ ...
0
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0answers
46 views

power analysis when mean and standard deviation are given

I have been asked to perform a sample adequacy test (i.e., I suppose, to verify what is the minimum difference that can be quantified between two grous) where a new sample (of which mu, sigma and ...
0
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0answers
85 views

Sample size calculation for paired t-test single arm using r

I am planning a study on alteration in AUC of a drug due to a surgery of gastrointestinal tract. It's a pre-post study. A group of patients will undergo blood sampling for AUC (area under curve) both ...
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0answers
30 views

Power of maximum likelihood parameter estimates for a linear model

The maximum likelihood parameter estimates for the linear model where $\Pr(Y|X\beta) \sim \mathcal{N}(0,\sigma^2)$ are: $$\hat{\beta} = (X'X)^{-1}X'Y$$ How do you compute the statistical power of ...
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0answers
93 views

Calculating sample size. Repeated measures within subject

I'm trying to calculate the sample size for a repeated measures within subject experiment. I'm going to test the subjects under 4 conditions and for each condition 6 measurements are taken at ...
0
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0answers
59 views

G* power for ANOVA repeated measures

I'm using G*Power to obtain an estimation of the sample size required. I have a 3×3 within-subject design (i.e., two factors,with 3 levels each). I used the partial eta squared of one of my ...
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0answers
35 views

What's the sample size required to confirm that two treatments are identical?

Goal: Determine if a machine is defective Say I am going to give the same treatment to a group of people. I have a machine that will randomly split them into $2$ groups before giving the same ...