Tagged Questions

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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0
votes
2answers
24 views

Choosing samples of different sizes - considerations?

Let's say I have four populations with the sizes 2451, 2117, 7577, and 1545. Each of these are sets of activity sequences on which I do sequence analysis. Based on this I want to do clustering based ...
0
votes
0answers
7 views

Sample size calculation using G*power for a mixed design

I have performed a pilot study in form of a 2x5 mixed design, with 10 participants. The factor with 2 levels was applied as a between subject factor, meaning that only a half of participants were ...
-1
votes
1answer
16 views

Sample Size Calculation of Pilot Study

I want to calculate the sample size for my pilot study. My subjects will undergo a certain test once taking a substance before the test, once taking a placebo. My goal is to find out if the substance ...
1
vote
0answers
6 views

Balance checking in randomized controlled trials with large sample

I have a survey experiment in which the treated group receives a certain prompt that the control group does not. I also have a bunch of demographic variables that I want to check for balance between ...
1
vote
0answers
14 views

Upper bound for sampling fraction for CLT to hold

What is the upper bound for the sampling fraction for the Central limit theorem to hold when sampling without replacement? Context The context for my question is that it is regularly argued (see e.g. ...
1
vote
1answer
32 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 ...
1
vote
1answer
31 views

The population size does not affect the sample size? [duplicate]

I used the following formula to calculate the sample size. n = (Z2 K p (1-p)) / i2; (k = 2, Z = 1.96, p = expected proportion, i = 0.03) I noticed that the sample size is not related to the population ...
0
votes
0answers
26 views

Sample size for logistic regression with categorical independent variables

Trying to find a sample size for logistic regression I found a rule of thumb in http://www.medcalc.org/manual/logistic_regression.php I cite: Sample size considerations. Sample size calculation for ...
0
votes
0answers
35 views

Getting Sample size

Annual starting salaries for college graduates with degrees in business administration are generally expected to be between \$35,000 and \$50,000 (Hint: Refer to the last slide of your Chapter 8 ...
1
vote
1answer
181 views

Why doesn't the standard deviation represent a normal distribution?

Why doesn't the standard deviation of a sufficiently large sample represent a normal distribution that we can make inferences from? Let me list my thought process, so hopefully someone can highlight ...
1
vote
1answer
15 views

problem: a sample size for the assumed effect in the 2 sample proportion test

I would like to calculate a sample size for the 2 sample proportion test when the significance level is assumed (0.05), power is assumed (0.90) and I'd like 2 sample proportion test to detect that ...
0
votes
0answers
17 views

number of participants/analysis

Hi I am really struggling here any help would be muchly appreciated, please use laymen terms where possible. research question: a comparison of quit rates between 3 smoking cessation treatments. ...
1
vote
1answer
39 views

Cohen's d in proportion test

I am calculating the sample size for proportion test. I would like to have significance level =0.05, power = 0.90 and that the effect size is greater that 5%. I would like to have statistically ...
1
vote
0answers
15 views

Problem Approach: uncertainty about sample size

I have a time series of events (weekly aggregate date) Each event is information on contracts closed by a sales representatives during working weeks. The goal is to calculate what is the expected ...
0
votes
1answer
36 views

Sample size problem

I am looking for a suggestions on how to estimate the sample size in such a problem. There is a group with one usefull treatment (let's say 10 milion people) but one consider if there might be more ...
0
votes
1answer
34 views

Linear regression sample size

I have about 80-100 participants and a single dichotomous predictor as fail/pass. My outcome variable is a continuous one and I want to know if my dichotomous predictor predicts the continuous ...
0
votes
0answers
33 views

Sample size calculation for non-normal data (possibly lognormal)

I am currently trying to rack my brains to find a solution but I seem to be coming up with nothing. I have water quality data with which I want to get a sample size calculation from for a future ...
0
votes
0answers
13 views

Optimizing selection from varying sets

On pages of website(s) I have a set of potential messages to choose from and only one or two slots to show them in. (think 'this product is on sale' or 'this product is new'). On each page the set ...
4
votes
1answer
87 views

Why is the sampling distribution of variance a chi-squared distribution?

The statement The sampling distribution of the sample variance is a chi-squared distribution with degree of freedom equals to $n-1$, where $n$ is the sample size (given that the random variable of ...
0
votes
0answers
10 views

How do I determine sample size to validate a requirement when I have a lot of margin?

I apologize if a similar question has been asked, but my search has yielded no results. I am having some trouble nailing down the correct methodology to use to design an experiment I am working on. ...
2
votes
2answers
109 views

Logistic Regression sample size & bootstrapping

The data for this example can be retrieved here so that you can reproduce these estimates. It is the low birth weight dataset- http://www.umass.edu/statdata/statdata/data/ There are 59 1's and 130 ...
0
votes
0answers
25 views

Calculate Sample Size with VERY small standard deviation

I am facing a problem trying to estimate sample size for an A/B website test I am currently running trying to investigate difference in revenue per click per day (RPVD). Unfortunately, this metric ...
1
vote
0answers
28 views

When comparing variability between unequal samples, is there a way to correct for sample size?

I am trying to compare test measurements taken at three time points in a training paradigm. The data for each test consists of a number of durations in ms. The variable I'm interested in is the ...
7
votes
4answers
533 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, ...
6
votes
2answers
136 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 ...
0
votes
0answers
30 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 ...
1
vote
1answer
119 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 ...
0
votes
0answers
23 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 ...
0
votes
0answers
18 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 ...
0
votes
0answers
16 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 ...
0
votes
2answers
101 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 ...
0
votes
0answers
28 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 ...
2
votes
1answer
44 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 ...
1
vote
0answers
30 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 ...
0
votes
1answer
45 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!!!!
0
votes
0answers
35 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 ...
0
votes
0answers
28 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? ...
1
vote
0answers
40 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 ...
1
vote
0answers
60 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, ...
0
votes
1answer
11 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 ...
1
vote
3answers
71 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 ...
1
vote
1answer
153 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. ...
0
votes
0answers
41 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 ...
0
votes
0answers
33 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 ...
0
votes
0answers
20 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. ...
0
votes
0answers
29 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 ...
1
vote
0answers
9 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, ...
0
votes
0answers
10 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 ...
0
votes
1answer
36 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?
2
votes
1answer
42 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: ...