sampling

  1. D

    HELP WITH DATASETS COMPARISON

    Hello everyone, I am a stats-beginner and I need help to understand if it is possible to compare two datasets. I am currently looking at the Residential Energy Consumption Surveys (RECS) databases, specifically to the 2015 and 2009 surveys. There have been some major changes in the 2015 survey...
  2. E

    Questions on the Fundamentals for Various Sampling Methods

    Hello, I've recently been studying various sampling methods, specifically SRS (Simple Random Sampling), Stratified Sampling, Ratio/Regression Estimation, and Cluster Sampling. I wanted to ask a few questions regarding these methods to better understand the pros and cons for each of them and when...
  3. J

    Sampling to find uniques in population

    The problem I am facing is: Imagine I have a bag of N marbles, where the value of N is known. In the bag there are k different color marbles. Our goal is to estimate the value of k. I take a sample of size n. The question is, how can I use this sample data to estimate the value of k?
  4. D

    Political Polling: Sample Size and Margin of Error

    Hello, My country have a proportional/majority system. I wonder how can a poll have a margin of error of 2.0%, if all the regional samples used in the poll have a bigger margin of error? - Southwest Region: N~64MM, n=880 and E~3.5%; - Northwest Region: N~39MM, n=553 and E~4.5%; - Central...
  5. A

    How to account for the subjects who are no more available for recording observations over time?

    Hello, I have taken a simple random sample in January, which is 10% of the population. Every month there is 10% people leaving the population, which will make my sample size also shrink. Over the time, there will a time where I will not have any subject left in my sample to record the...
  6. U

    What is the reason behind getting unbiased and efficient estimator by ranked set samp

    In ranked set sampling (RSS), we select n random sets, each of size n. Then we choose the largest unit from the 1st set, 2nd largest from the 2nd set, and thus n th largest from the n th set for the actual measurement. What is the intuition that a sample thus obtained will give an unbiased...
  7. G

    interesting sampling question

    I have two samples of the same population and wish to reduce the sample sizes, but maintain the same ratio of precision produced in the original samples. I suspect I can take the square root of the original sample size, but this produces very small samples. How, in short, can I scale down the...
  8. A

    Comparing an ecological subsample to population

    I have 2 batches of tree species and abundance data collected for a city. The difference between them is the sampling strategy - one was random unstratified, and the other was stratified and clustered. At a glance the species mixes and relative abundances are fairly similar but i want to test...
  9. L

    sampling/probability/correlation?

    I have in my course this problem do you have any idea from people who work daily with stats ? the question is like that: the following data are available concerning the products of a firm taken at random from four factories, and classified according to level of quality: Factory A : from low to...
  10. rogojel

    testing the bootstrap

    hi, below is an experiment I just did testing whether using a bootstrap I could get better results as with simple repetead sampling. Is there any error in the logic/code? It seems that bootstrapping would just amplify the sampling error without adding any value - what do I miss? This is...
  11. A

    [Sampling] Which type of sampling to use in this case

    I would appreciate any help in this case took from a book (without answers and tips): Consider that a court wishes to evaluate the proportion of inhabitants in some municipality who were victims of some type of violence and there is no database with the identification of the inhabitants of...
  12. S

    Question on sampling without replacement

    Here is a question regarding sampling without replacement. Say there is a class size of 24, and the teacher is breaking students into groups of (4) for project work. The teacher selects the groups by putting all (24) names into a hat, then drawing (4) at a time. What is the probability that (2)...
  13. H

    sampling method

    Mark wants to evaluate the GPAs of current NYU undergraduate students. He has received a list of all current students from the registrar and wants to take a probability based sample from this list. If Mark wants to ensure that his final sample is comprised of 30% freshman, 25% sophomores, 25%...
  14. H

    Sampling Techniques

    Which sampling techniques would be most appropriate if the researcher’s goal is to make statistical inferences from a sample to the population?
  15. D

    Generating confidence intervals for both height and weight with the same sample?

    Given that height and weight tend to be correlated, would it be okay for me to use a single simple random sample of people to create confidence intervals for both their height and their weight?
  16. sepinaz

    Can we model the experiments as a stochastic process and estimate the sample size?

    I have an image with the size `5575x9440` and I'm implementing a modified version of the algorithm used in this paper on it, but because the code performance is low right now, I have divided the image to `52628` submatrices of the size `25x40 (1000 pixels)` and my first experiments show that...
  17. L

    Sampling issue

    I want to be able to make comparisons between a specifically selected sample (based on ethnicity) and a randomnly selected sample from the general population. Even though the specific ethnicity represents no more than 10-15% of the population, my randomnly selected sample from the general...
  18. D

    sampling question.

    I was given this question and I'm looking for an answer. The question is.. "The client of an email process has specified that the % of A or B quality transactions should exceed 85%. The program is current operating at 75% of A or B scores. The client can tolerate a measurement error of 2% and...
  19. C

    Calculating the amount of underestimation

    Coverage rate for a parameter is 91.2%, and the nominal coverage rate is 95%. If the confidence interval is based on asymptotic standard normal, then the amount of coverage 91.2% implies that the standard errors for the parameter is estimated about 15% too small. Because z* value used to make a...
  20. C

    Simple Algebraic Calculation about underestimation

    In a findings, it is found that the non-coverage rate for the second-level intercept variance is 8.9%, and the non-coverage rate for the second-level slope variance is 8.8%. Although the coverage is not grotesquely wrong, the 95% confidence interval is clearly too short. The amount of...