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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5 views

How to sample when you don't know the distribution

I'm fairly new to statistics (a handful of beginner-level Uni courses) and was wondering about sampling from unknown distributions. Specifically, if you have no idea about the underlying distribution, ...
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2answers
77 views

5 defectives rule of thumb

I have taught six sigma black belt classes using consultant sourced training materials which included the rule of thumb that when estimating the rate of occurrence of discrete events, like the ...
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0answers
23 views

non-parametric tests with significant difference in sample sizes

I have outcomes from a biological expt., where we have measured DNA lengths that has been affected. For condition1, I have 11 observations (length of DNA) and for condition2 I have approx. 116000. I ...
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20 views

Weights in Weighted Least Squares Regression

Let's suppose I have the following linear model: $R = \beta * X + \epsilon$ I have a cross-sectional time-series sample of $n$ stocks, at $T$ periods of time. Not all stocks necessarily have data ...
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1answer
106 views

Finding the sample space of an experiment

Suppose that a study is being done on all families with one, two, or three children. Let the outcomes of the study be the genders of the children in descending order of their age. List the sample ...
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18 views

appropriate sample size to fit non-normal distribution parameters

I have a population that, in theory, I could determine exactly. I am not doing so, however, because on my poor home computer, it would be too computationally intensive. Each calculation takes 45-90 ...
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0answers
5 views

small observations but many independent variables for multiple regression, can i have dummy variable?

The dataset i have consists of Y(N=80) and X(60 IVs). they are all numeric. I run multiple regression using two variable selecting methods: 1. stepwise 2. all possible regressions. I get very high ...
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0answers
10 views

randomForest sample size value formula

This question has been asked previously, but the answer didn't contain a formula - only a rule of thumb heuristic. Is there a formula or rule that exists for determining the appropriate sample size ...
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2answers
58 views

What's the minimum sample size required to do a time series analysis?

I'd like to know the minimum number of monthly data points required to do time series analysis with the seasonality effect in forecasting. I read some articles & they were saying that 50 or 60 ...
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19 views

How to calculate a required sample size for an estimate of the population total $\tau$ without knowing the population variance $\sigma^2$

To calculate a required sample size $n$ for estimating the population total $\tau$ (which is equal to $N\mu$) with a pre-specified error bound $B$, the formula is: $$n = \frac ...
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1answer
36 views

mean of population with repeated samples of varying size - how to apply CLT?

I have a population with mean $\mu$ and variance $\sigma^2$. I draw a sample with $n_i$ number of i.i.d random observations from population. I compute the mean for this sample as $mean_i$. I then ...
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23 views

Cross validation with unequal sample size for the left out sets

I am trying to do cross validation on several (20) subsets of samples, which all have unequal sample size. I cannot subsample so that sizes are equal. Example: batch 1: 500 samples batch 2: 400 ...
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1answer
40 views

Calculating sample size in R

I'm trying to calculate sample size and I have a Cohen F of .25, and I want to use power of .8. Is there a function in R that will let me calculate sample size based on these values? THANKS!!!!
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0answers
23 views

How to calculate sample size for poll / ranking

Let's suppose there are Y options to choose from. I'd like to run an experiment with a sample of n participants (from a larger population), each will choose 1 option from the Y alternative according ...
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0answers
27 views

How big a sample size do I need to say a player is performing below average on penalty shots?

An average ball player scores 20% of his penalties. How many penalty results would I need to receive before I can say that a player scores at a rate of 15% requires coaching on his penalty shots? ...
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0answers
39 views

Small $R^2$ Despite Clear Difference in Totals Between Groups

I have a very large set of products (1000+), each one contributing a certain amount to total revenue. Product profit for purposes here can be negative. I decided to use a binary indicator variable ...
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0answers
40 views

How to determine the correlation between data sets with the same period but different sample rates?

I am trying to determine the correlation between two sets of data points which span the same time period (20 minutes) but have different resolutions. The first set was recorded at 1-minute intervals, ...
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1answer
9 views

Appropriate sample size for paired t-test--forest measurement

I am trying to conduct a paired t-test to detect if there is a difference between the mean value of a parameter calculated by another person and myself (carbon stocks of forest types) but am unsure of ...
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3answers
69 views

smart sampling techniques in r

I have a large data set of about 1.8 million rows with 80 variables. I would like to find a good technique (code or package) in R that can reduce the amount of training data without damaging the ...
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1answer
142 views

What if the trend is changed?

I want to forecast tourist arrivals using time series analysis. I expected to use monthly data from 2000-2013. But due to the civil war, the trend was changed after 2008 as in the following plot. ...
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0answers
25 views

Sample size for a moderated hierarchical multiple regression analysis?

I am having a challenging time finding out the necessary sample size for a moderated hierarchical multiple regression analysis. The first five steps of the regression will include the 17 variables ...
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0answers
17 views

Comparison of average variances between groups of different size

I have 3 groups, split by highest degree of education. For each individual in a group, i calculate the variance of her income in a five year window. Let's for simplicity assume that i only do this ...
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0answers
17 views

Sample size for validating a prediction model

Dear friends: In an earlier pilot study a third- degree polynomial model was built, X = time (days) Y = Moisture loss. I need to validate this model in a larger study with more samples. ...
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25 views

Sample size and power calculation

I am looking for an advice on sample size and power calculation for an intervention study. The study uses a stepped wedged design. The study aims to evaluate the effectiveness of case managers ...
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0answers
8 views

How to calculate MoE for subsamples

I have demographic and income data for 3 million people from the American Community Survey (courtesy of IPUMS), and my goal is calculate the median income for every permutation of age group, gender, ...
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0answers
9 views

Sample Size for GWAS study

How to calculate sample size in a case control study with given number of SNP are 200 and 10 environmental factor. Here I assume 90% power and 5% significance. Or in short what are the inputs required ...
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1answer
30 views

Sample size for ANOVA

Is there minimum sample size for each group in 1-way ANOVA? if yes, please give a reference(s), If no, why there is not?
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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
54 views

Partial sorting: select at most N elements including for sure the top T elements

To whom it may concern. My "population" with known size P is a landscape and has not more than 4 peaks with about same high. Naturally top elements group locally within the population. I seek the top ...
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0answers
19 views

Unbalanced groups in a Hierarchical Linear Model

I would appreciate some practical and/or conceptual advice on sample sizes in a two level hierarchical linear model. A lot of the material on sample sizes and HLM is about the number of level 2 ...
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0answers
21 views

Calculate statistical power on groups with different size

Is it technically possible to calculate the statistical power for a test where the two groups don't have by design the same size. I'm thinking to a 90%-10% split of the population. Namely, is there a ...
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0answers
80 views

How to deal with unequal sample sizes while fully embrace a dataset?

Imagine the situation: Mythical Seafolk use holes in the seabed as their burrows. Each hole has two parameters - diameter and depth. Majority of holes are unoccupied due to their surplus (n = 235). ...
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0answers
20 views

Determine sample size according to some unknown distribution with given error rate and confidence

Assume $x\in\mathbb{N}$ obey some unknown distribution, and I can sequentially and independently acquire infinite samples of $x$. Now, given an error rate $\epsilon$ and confidence $1-\delta$, can I ...
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2answers
109 views

How to choose the training, cross-validation, and test set sizes for small sample-size data?

Assume I have a small sample size, e.g. N=100, and two classes. How should I choose the training, cross-validation, and test set sizes for machine learning? I would intuitively pick Training set ...
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17 views

How to equalize lower accuracy on larger sample sets?

I have a collection of image samples that I want to OCR. I also have the ground truth of the text on these images. Now I OCR them and eg. 10 of 100 samples are wrong. So I got an accuracy of 90%. ...
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1answer
70 views

Formula for calculating sample size for hypergeometric distribution

Suppose you have an urn with "N" marbles. All marbles are either black or white. You take a sample of size "n" without replacing them to the urn. With this one sample you would like to be able to ...
2
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2answers
69 views

How to predict the amount of data needed for modeling?

Is there a way to estimate the amount of data (or the number of records) required to build a statistical model? I read few blogs and I feel that most of the responses concur that there is no way or ...
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0answers
25 views

Filtering Samples of Unequal Size and Correlating Categorical with Non-Categorical Data

Suppose I have a large number of samples, some of which only contain one observation, and some of which contain up to 12. Each observation can fall into one of four categories per sample. This ...
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25 views

How to find number of samples needed for a 95% confidence interval

I wish to perform a number of tests, what are the minimum number of tests I need to perform to be 95% sure the mean of the test is significant to within ±10% when I repeat the test ? As one example, ...
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2answers
202 views

Bootstrap: the issue of overfitting

Suppose one performs the so-called non-parametric bootstrap by drawing $B$ samples of size $n$ each from the original $n$ observations with replacement. I believe this procedure is equivalent to ...
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2answers
50 views

Test for equality of coefficients from 2 different samples

I have a model that I fit on two different samples (each representing a region in a country, with different sample sizes): ...
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0answers
18 views

Determining Sample Size to Show Increase in Disease Prevalence

A prof and I are trying to figure out how many samples a study would need to show a certain % increase in disease prevalence, but I'm not sure I'm doing this correctly. Basically we want to know how ...
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0answers
19 views

Finding the fewest needed samples for a regression method

I have a regression method that I have applied with success to tens of thousands of well-observed objects. I'm looking to estimate how well it works on poorly observed objects. I selected 50 objects ...
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1answer
182 views

Is bootstrapping appropriate for this continuous data?

I'm a complete newbie :) I'm doing a study with a sample size of 10,000 from a population of about 745,000. Each sample represents a "percentage similarity". The great majority of the samples are ...
2
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1answer
58 views

Approximating sample distribution standard deviation

I've seen in video lessons that if the sample size is big enough (n>30) sample distribution standard deviation can be approximated by sample standard deviation. How do we get the sample distribution ...
2
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1answer
72 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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0answers
50 views

Sample Size Problem with Tukey HSD Test

I was planning to use a Tukey HSD test for the following data, as it was used in a study with a similar approach. I regressed stock data for three time ranges (1 year daily data, 2 years weekly data, ...
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1answer
104 views

Paired $t$ test - Different Sample size

In testing the difference between a 'pre' survey group and 'post' survey group, I have the same sample population surveyed, yet different sample sizes (fewer respondents within the 'post' group). Am I ...
0
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2answers
32 views

Cross Vaidation in Factor Analysis

I am trying to conduct an EFA with a sample size of 150 respondents. I would also like to use cross-validation but my professor says that the sample is not big enough for that. Is that true?
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1answer
38 views

Taking a random factor into account while measuring a proportion a low N

I need to be neat in measuring the success rate of a treatment. It is anyway pretty high. But as it is all about ecology, multpliying experiments is difficult. I have treated $N = 20$ individuals, ...