Tagged Questions

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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1answer
38 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 ...
1
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0answers
29 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
21 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
21 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
61 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
27 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
23 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
39 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
41 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
26 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
33 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
118 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
48 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
32 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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0answers
70 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
74 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
72 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
43 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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0answers
33 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 ...
4
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2answers
191 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
27 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 ...
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0answers
28 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
15 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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0answers
31 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
48 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
139 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
16 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
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1answer
217 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
93 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
40 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) ...
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0answers
109 views

Minimum sample size for a dichotomous outcome

I have two questions. I am running an experiment where I am interested in determining the sample size required for a certain CI and error, where values range between $<1$ and $>-1$. However, I ...
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0answers
29 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
62 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 ...
1
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0answers
27 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
57 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 ...
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0answers
37 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
31 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 ...
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0answers
25 views

Calculating power for a survey to compare different metrics

I am currently planning a survey. The data will be used to test which of three metrics best captures some "true" underlying characteristic of the respondents. Getting data on the "true" underlying ...
0
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1answer
46 views

Designing Frequentist A/B Experiments

What parameters should one pre-specify before designing/running an experiment? (e.g. a two-sample, one-side, t-test) My understanding is that on establishes: Null hypothesis Maximum Significance ...
3
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0answers
38 views

Estimating Sample sizes for Null Hypothesis Testing

Wikipedia has the following table for computing sample sizes:                                       ...
1
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1answer
58 views

Is the variance of the residuals of a linear regression useful for estimating experimental sample sizes?

I have a data set of $y$ values that is not particularly normally distributed. However, the $y$s do partially depend on several other parameters. A linear regression model $y=c+\mathbf{ \beta ...
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0answers
26 views

power for estimating treatment heterogeneity in RCT

Could someone point me to a good resource for estimating power for detecting treatment heterogeneity via interactions in MR? Let's assume that individuals will be randomized to two study arms. To ...
3
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0answers
29 views

Power in proteomics?

Grants often require power analysis to support a proposed population size. In proteomics (and most -omics), there are 100's to 1000's of features/variables measured across 10's of samples (maybe 100s, ...
2
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0answers
71 views

Sample size requirements when studying total population

I work for a fundraising organization and we want to implement an A/B test to determine if a particular donor recovery technique is working. The population under study is our lapsed donors. These are ...
0
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1answer
19 views

How to perform power analysis for repeated measures with observation error?

I am interested in producing two raster maps of the same areas but separated in time. I would like to take the average value of all pixels in each map and test if there is a difference in that mean ...
0
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0answers
32 views

Is unpaired t-test appropriate for 2-level random cluster sampling? Also, how does this affect the power of the test?

I'm working on power/sample size calculations for a non-profit and want to make sure my logic is correct, as I haven't worked with a situation quite like this before! This is a bit of a long post, as ...
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0answers
32 views

Power analysis in meta-analysis: Compute the maximum significance needed by an additional sample for meta-analysis to reach genome-wide significance

I have an association study analysis (GWAS) that does not reach genome-wide significance (max p-value < 10E-5), and there is a potential additional sample (so with known N and known effect size/SE ...
5
votes
1answer
75 views

Power analysis for post hoc test of ANOVA with many groups

In both G*Power and the R pwr package, estimated sample size required per group decreases as the number of groups increase. This seems somewhat counter-intuitive. For a toy example, assume that I ...
5
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1answer
97 views

Power when using binomial data versus continuous data

I have a question about something that is probably very basic to statistics but I feel I don't fully understand I've found that generally it is much harder to get high power (smaller) confidence ...
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0answers
81 views

Power Analysis: Comparing GLM to binomial proportion test

I am trying to run a power analysis using simulated data to compare the power of a glm versus a binomial proportion test to detect differences in proportions. For example, suppose you have some ...