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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1answer
21 views

Interim analyses without any stopping rules

I've got some questions about interim analysis rules. Do I need to make alpha/beta corrections in the following situation: One interim analysis is planned in the study The interim analysis is ...
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0answers
18 views

Relation between precision, recall and sample size

I have a large data set for binary classification problem. Now in order to fit model to data I have been trying modeling using various sample size. For each sample size I gets a different precision ...
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0answers
5 views

3-arm RCT with black vs white comparisons

I am trying to design a 3-arm randomized controlled trial - intervention A for group 1, intervention A+ B for group 2 and control group for group 3. I would also like to look for black vs white impact ...
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0answers
16 views

Do the number of choices in a A/B test affect sample size needed for statistical significance?

I apologize if I sound too stupid, but my statistics knowledge is very basic. I'm a software engineer and I'm conducting an experiment over web page conversions in which I'm trying to determine the ...
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0answers
30 views

For a U-shaped distribution, how many results must I verify

--edit-- in plain English. I have a distribution with over a million points between 0 and 1 that is shaped like a U with many values falling near 0 and 1. Each point is SUPPOSED to represent a score ...
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1answer
68 views

How much sense does median of one number make?

Median of one number = the number itself. I am calculating the median price sq ft of properties of different areas based on the different data entries I have got that include their ID, area and ...
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0answers
6 views

How to calculate sample size for testing H0: Y is related to X by a sigmoidal function?

I'm assuming I would need to specify a given functional form and conditional standard deviation for Y at each X. That would give me some parameters to be estimated and I would need to set a threshold ...
3
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1answer
53 views

Sample size for best forecasting ARIMA model

How can we decide the size or portion of the data given to get the ARIMA that has the best forecasting properties? I mean, for example, we have a hourly series with over 28.000 elements. Which is ...
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1answer
23 views

Minimum business sample required to do correlation analysis

I'm doing a bit of business analysis at division level for a company. I'm interested in determining if there is a relationship between engagement (and other people metrics) and financial performance ...
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0answers
27 views

Sampling rate and regression

I am interested in developing a regression model. The data (about 1000 observations) that I have are not really random (i.e., spatially, the closest ones are correlated to some degree), so I drew a ...
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0answers
7 views

a cross sectional study on factors affecting iq level among medical students

I am an undergraduate medical student. I have a question on how do i determine my sample size if i am running a cross sectional study on factors affecting iq level among medical students. I am ...
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0answers
6 views

Minimum sample size to establish a cutoff point

I conducted a case-control study (obese and normal body weight). I want to conduct ROC curve between my variables to establish a cutoff point for vitamin depending on insulin resistance risk. Does it ...
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1answer
30 views

Standard deviation for probability (multiple choice)

In a multiple choice test with 4 answer options, the probability of guessing correct is 25% (assuming you have no knowledge about the materials at all). Thus, regardless of sample size, my estimated ...
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1answer
16 views

Derivation of formula for sample size of finite population

I found here the formula for computing the sample size $n$ of a finite population $N$ $$ n = \frac{n_\infty}{1 + \frac{n_\infty - 1}{N}} $$ where the sample size for an infinite population $n_\infty$ ...
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1answer
60 views

Why does chi square test seem to depend on sample size?

This question relates to my ENT anti-answer in another forum, but is based on a statistical perspective. Traditionally, the chi test does not depend on how many samples you take, so it should be as ...
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0answers
7 views

Sample size for incidence rate (based on relative error)

I have a problem with sample size estimation for incidence rate based on relative error. There is a sample size formula on two published books one of them a book from WHO (sample size determination ...
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0answers
22 views

Why do needed sample sizes for ANCOVA versus OLS differ so much?

I am planning a study of the effect of an intervention on two groups. While computing the appropriate sample size (using GPower) for the study, I noticed that ANCOVA requires about 4x the sample as an ...
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0answers
4 views

Determining significance and power of a test with fixed sample size

I have a total population of 70K members and I 12K "kits" that I want to send out to a randomly chosen group to test if the cancellation rate is lower vs the control (so test group is 12K and control ...
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2answers
49 views

Difference in Group Sample Rate, not Size, based on Independent Variable

I'm working on a study that involves measuring breathing effort of an individual over short periods of time (specifically breath distention). The dependent variable is based on a new therapeutic and ...
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0answers
14 views

How to determine the proper sample size and testing criteria range for an experiment design?

I am currently trying to design an experiment that will be testing how fast a conveyor is able to convey different size cases. The case sizes are based on 4 dimensions (LxWxH and Weight) and the case ...
3
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0answers
21 views

Formal method to find optimal sub-sample size from large sample for multiple regression

I have labour market data for 9 million observations, for a single time period (i.e cross-section data). I am studying the determinant of wages in a single equation multiple regression with around 300 ...
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3answers
57 views

What lowers the p-value besides the sample size?

The title pretty much says it. Sorry, it's so unspecific, I am not asking the question for myself and I am not familiar with stats.
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0answers
14 views

Relationship between pval and sample size with >2 categories

I know that in general an increase in sample size results in a decrease in the p-value, sample mean being held constant. However, say that i have one categorical predictor variable with three values, ...
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0answers
31 views

Sample size needed to detect a three-way interaction?

I am hoping to propose a study for which the predicted outcome would be a three-way interaction. I am wondering if this is going to be possible at all with the resources at my disposal, or if the ...
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1answer
217 views

Consequences of exceeding sample size after determination of sample in power analysis

Challenge In our office, I have been involved in a discussion about sample size and its influence on effect size - can you help me out and explain further? Base When conducting a power analysis, ...
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0answers
53 views

Can survey sample sizes be used for quality control sampling? Is the formula that easy?

I have no solid background in statistics so please bear with me. In general, I am trying to figure out methods to determine sample sizes required to establish a certain level of confidence for a ...
0
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1answer
25 views

Multilevel models

I would have a question on multilevel models, which is related to a particular case that I am considering. The question is related to the number of my groups and the number of measures in each of ...
0
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1answer
59 views

Determine required sample size with unknown standard deviation

An exercise : A quality control engineer gets 1000 items. How big a sample will he require to say that the he is 95% confident that the sample represents the population?? Is this possible to answer ...
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1answer
28 views

Estimation of sample size for stratified randomized clinical trial with R

We want to conduct a multi-center randomized clinical trial with two arms (2 treatments : a superiority trial) stratified on three centers (three sites). The primary outcome variable is a continuous ...
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0answers
8 views

Sample size gamma regression

I would be very grateful if you could please advise on sample size.... I have estimated a sample size using R - library(pwr) using command "pwr.f2.test(u = 6, v = NULL, f2 =0.02 , sig.level =0.05 , ...
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0answers
25 views

Is there any rule of thumb regarding sample size for multinomial logistic regression?

According to Applied Logistic Regession 3rd Edition by Hosmer and Lemeshow, the acceptable rule is minimum of 10/5-9 events per binary logistic regression parameter so as to not overfit the model. ...
3
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1answer
59 views

Sample size to use with a linear regression model

I am testing an automated counting method. To measure its effectiveness I am doing a linear regression model comparing the manual approach to the automatic. This gives me an F statistic for the model ...
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1answer
34 views

Can increasing the significance level help to avoid detecting minor differences in large datasets?

In the accepted answer of THIS question, it is stated that "With such large sample sizes both tests will have high power to detect minor differences". On the other hand, a voted up comment in THIS ...
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0answers
7 views

Interim Analysis for Futility in a 1-Arm Trial with a Binomial Outcome

I am planning a 1-arm trial that tests a response rate in patients to a drug. The response rate indicative of the drug working would be 30%, and 10% would be considered the null response rate (i.e., ...
3
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1answer
24 views

Document classification sample size

I'm working on a document binary classification problem where I have a decent sized corpus of about 30,000 documents (600-1000 words each). My approach is to select a sample of documents and manually ...
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0answers
12 views

Graphing statistical significance in R for an A/B test

I've never graphed anything in R relating to statistical significance. These are the results of an A/B test. Here are the specs: Sample 1 (Successes/Trials): 20/1224 = 0.91% Confidence Interval ...
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1answer
36 views

Sample size for SEM with ordinal measures

I'm in the early stages of planning an analysis which would involve a large number of ordinal variables, and I'm trying to work out if I have enough observations in my sample. The ordinal variables ...
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1answer
50 views

Sample size question, 7 samples with different sample sizes

I am looking at the measurements of different organisms (in nanometers). I have 7 different populations. 1 is what I know the origins of, and I want to compare the size of this to my other 6 ...
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0answers
7 views

Number of Questionnaires and sampling frame

Do the number of questionnaires used in a study affect the number of participants in a sample frame? If so, how do I estimate the sample size based on the number of questionnaires (during pre-test, ...
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0answers
10 views

How to apply the finite correction error to adjust the required sample size

I am currently refreshing my stats knowledge where I came across the notion of the finite population correction. This notion appears when determining the sample size required to construct a confidence ...
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1answer
31 views

Confused about the sample size in large sample confidential interval and population proportion intertal

My professor said when sample size is large, it will has the following formula, but how big is the sample can be considered to be a large sample and use the following formula? I did some questions ...
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1answer
154 views

Unable to reproduce paper results (sample size)

I am interested in using the results from this paper (Modified exact sample size for a binomial proportion with special emphasis on diagnostic rest parameter estimation by Geoffrey Fosgate) to ...
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0answers
19 views

Estimating actual score from small sample when population known

My inclination here is that there's no statistically sounds way of doing this, but I want to verify this. Suppose you have a population P, and you are measuring test scores across the population such ...
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0answers
12 views

Sample size for correlational study

Hi signed up for this site just to ask this question so any help would be appreciated. I need help determining the sample size by using an a prior method of analysis The power needs to be 0.8 and ...
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0answers
11 views

Estimating Sample Size of Log Scaled Data

I apologize if this is a simple question or has been answered already, but I'm a little stumped and I'm not a stats person. I am trying to optimize a system I am working on where we make absorption ...
2
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1answer
27 views

Sample similar to Population

I have 100,000 customers, each customer has a few variables associated with them, separated into 100 groups. I want to find a sample of 10 groups that best represents the entire 100 groups. What are ...
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0answers
31 views

Calculating the required sample size for a 2x2 repeated measures ANOVA?

I have conducted an experiment with two independent variables, each with two levels. I had one group of participants who were tested under four conditions. I have performed the ANOVA using SPSS, and ...
1
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1answer
12 views

Can interactions save power in a regression (vs. stratification)?

I have data with about 700 observations total. There are 9 subgroups in my sample with sizes ranging from 54-96. I want to use linear regression to explore how 8 independent variables might predict ...
0
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0answers
42 views

How to get event hazard rates from a survfit object for sample size calculation

I want to calculate the sample size for a clinical trial (right-censored time to event data). I have data of a retrospective analysis and would like to use nSurv ...
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0answers
11 views

Effect of sample size on generalizing to a broader population

What effect will sample size have on your ability to infer your sample findings to a broader population?