sample

  1. M

    How to sample permutation in r without repeating permutations in R

    Hi guys. I was wondering is it possible to create a matrix or a vector of permutations without repeating them. E.g. create a matrix of 4! = 24 permutations. The way I started is: k <- 4 n <- factorial(k) x <- matrix(NA,nrow= n, ncol =k) for (i in 1:n){ x[i,] <- sample(k)...
  2. J

    Logistic Regression

    Hello, I'm currently working on a churn modelling exercise that uses logistic regression. The challenge that i'm facing now is that the model is not returning good results. My hypothesis is that the churn rate in my data set is too small, such that a logistic regression was not able to pick...
  3. M

    When to use which statistics? Is it correct like this?

    I never had statistics in school and I'm not in college yet so I try to teach in to myself now. That's why everything I write now could be plain wrong: - You use hypothesis tests (independent t-test, paired t-test etc) to test a claim about a population mean/population proportion or to test a...
  4. D

    Theoretical Question Operational Data What is Sample and what is population.

    Hi all. I'm working on operational data of clinical operations, attendance, performance and employee performance. I'm trying to use statistical methods to make regressions, correlations and predictions but I don't know if I should use the mean value and variance for the "sample" I have...
  5. M

    Sample based on 2 stratas/variables

    Hello guys, I have a dataset of 90 observations (health center types). I only need 30% of my cases. I have two stratas/variables (I guess): Region and Hospital type. There are 10 US regions and 5 health center types such as family planning, state dept. etc. How can I do this? what would be...
  6. K

    Confidence interval of mean of queue length (M/M/1)

    Goodday, For a simulation course I had to simulate a single server queue with Poisson processes for arrival and departure (M/M/1). Now, this really was not the issue, the issue is where I personally want to add a kind of validity check, which naturally can only be done with statistics. I...
  7. H

    Resampling in R

    Hi I want to generate two sets of random numbers and see how many times the same number appears in both columns. In R I have been using the code length(intersect(sample(1:369, 51, rep=F), sample(1:369,13, rep=F))) I would like to replicate this 1000 times, each time with a new set of random...
  8. A

    Comparison of two treatments (paired and unpaired)

    Hi all! I'm working on my Master thesis and need to make sure I'm not doing it wrong. My research: Are answers to questions a and b significantly different from one another, and why? Questions a and b are answered on a scale from 0 to 10. My data: 153 survey responses, split into 3...
  9. J

    Basic Sample Sizing Question

    Hi all, I haven't done any stats for a long time, I am looking to incorporate some stats into my Ops Risk role to get a little edge. I think I am on the right track with this first little attempt but just wanted to run it by the forum for any feedback. So at work, we are starting a new...
  10. S

    Sample Representativeness

    Hi guys, I am doing analysis on a sample to figure out the sentiment of a population. In my data I have various demographics of the respondents and their rating indicating their satisfaction with a company. I want to make sure the sample is representative of my population. For this I plan to...
  11. S

    Sample difference in repeated designs with control

    Hi everyone, as my computer crashed a few days ago, I lost the source to an article I was reading referring to how large the sample size deviation in repeated measures can be between treatment and control group. If I remember correctly it cited Stevens (might have been Student though) on how...
  12. I

    What is booster sampling?

    We are doing convenient sampling rather than random sampling for a research that we are conducting. The authority is concerned about the reliability of the sampling. They have suggested that we look into booster sampling. Can any of you please let us know more on this? or redirect to...
  13. N

    testing errors in true among several services

    We want to be able to estimate by product the percent of prices recorded differently that in written contracts. Verification is costly. I am thinking of sampling a fixed n for each group to find a pricing error which will need to be done by hand. I'm assuming the pricing error is normally...
  14. M

    need formula can youn help?

    find minimum sample size P(s2/sigma2 <1.75) >.95
  15. M

    dependent or independent

    Dear Sirs, I have situation in which I query different sites on the genome (biologically independent) and for each site I get a measurement. I have a number of measurements that are close together on the genome and I call that a region. I then want to compare the measurements of a region...
  16. A

    How to create a representative sample?

    Hello to all! :) I have recently launched a survey to students of specific universities among European countries and got nearly 3000 replies. However my sample is not balanced, meaning that some countries provided many replies, while some others just few. I want to analyse my results at...
  17. C

    help? hypothesis test selection and execution

    Hi. I am trying to figure this out and I'm not sure if I am doing it right. a) did I select the correct type of hypothesis testing??? b) am I using the numbers in the right place (I have SD for 3.5 for pop and 2.86 for sample. which one is right for my hypothesis and equation?) c) what else am...
  18. W

    proportion of a sample

    Hi. Could someone help me answer the last 3 blank boxes? I got 0.2, 0.05 and sqrt(0.2*0.8/150) for the first 3 boxes. A researcher in Food Science is interested in estimating the degree of cracking of a certain variety of rice under a certain regime of industrial rice dryer. The quality...
  19. S

    Proper Sampling - Can i sample like this without destroying reliability?

    The population that i need to extract a sample from is all firms from country A with activities in country B. The firms are classified into two categories: as having a subsidiary in country B, or not having a subsidiary in country B (the activity could then be exports, which does not require a...
  20. S

    Help with Sample Space question.

    Q: There are n marbles in a bag and k(k<n) of these marbles are marked. i) Marbles are drawn from the bag at random (without replacement) until one marked marble is dawn. Write out the sample space for this experiment. ii)The experiment is reset and this time marbles are drawn until all marked...