sampling

  1. 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...
  2. J

    Checking the Independence.

    Let X_i\sim N(\mu,\sigma^2) ; where [i=1,2,\ldots,n] Z_i\sim N(0,1) ; where [i=1,2,\ldots,n] Proof that \frac{(\bar X-\mu)}{\sigma} and \sum_{i=1}^n\frac{(X_i-\bar X)^2}{\sigma^2} are independent, which implies \bar X and \sum_{i=1}^n(X_i-\bar X)^2 are independent. If i show that \bar...
  3. J

    Cumulants of non central chi-square distribution

    Cumulant generating function is defined by logarithm of Moment generating function. K_X(t)=\log M_X(t) let X is a non central \chi^2 variate with parameters degrees of freedom,n and non-centrality parameter,\lambda. Moment generating function of X is...
  4. S

    calculating p-value from resampling of the null distribution

    Hi all, i am a PhD student in Bioinformatics and i'm dealing with some statistics issue in my reasearch; i was hoping you could lend me a hand :D I am dealing with a pool of datapoints (let's call it Q). I selected a subset of Q according to some particular characteristics, i will call...
  5. B

    Sampling a hemisphere using an arbitary distribtuion

    I am writing a ray tracer and I wish to fire rays from a point **p** into a hemisphere above that point according to some distribution. 1) I have derived a method to uniformly sample within a solid angle (defined by theta) above **p** [1] \phi = 2\pi\xi_1 \alpha = \arccos...
  6. O

    Generating a multi-parameter space and sampling from it

    Hi all, I have a long list of combination of parameters which covary. I would like to sample from it but not exactly the same values. What I'd like to do is to create a multi-parameter space that accounts for the covariation and then sample from it the parameter values to create new...
  7. S

    OC Curve Program

    One of my friends has asked me to help him write a program to calculate the "n" and "c" values (sampling size, accept number), only given alpha(confidence level) , beta(probibility of acceptance), p1(AQL) and p2(LTPD). I'm currently a computer science major that has taken a few statistics...
  8. S

    Sample design problem

    A healthcare provider has been paid on N claims for certain health services, some of which may have been unauthorized. I must draw a sample of n claims to estimate the total payments to this provider for unauthorized claims: Y = Sum of I(k) * X(k) for k = 1 to N where: I(k) = 0 if claim k is...
  9. C

    which sampling methods-reply ASAP

    For some statistics course work, I am investigating two hypothesis', and I am not sure which sampling method I should use. They hypothesis' are: the accuracy of estimations of the size of an angle is more accurate when on white paper with black lines, and The accuracy of an estimation of the...
  10. B

    How to program a Ranked Set Sampling in R?

    I am trying to program a ranked set sampling using R. There are 2*n^2 items and I want to randomly divide them into two equal sized groups with n^2 items in each group. Then I want to use a Ranked Set Sampling from each of these groups to form n RSS blocks with n items in each RSS block. What...
  11. W

    Sampling from N data points based on a given probability distribution

    I have N data points, and each data points is associated with a probability. The sum of the N probabilities equals to one. I need to sample these N data points based on the given probability vector. Are there any algorithms that can allow me to do this kind of sampling?
  12. F

    Sampling Distributions help

    Hi, I'm teaching myself stats but have no idea on how to solve these, any help would be appreciated. When a pizza restaurant’s delivery process is operating effectively, pizzas are delivered in an average of 45 minutes with a standard deviation of 6 minutes. Suppose each night, 9 deliveries...
  13. M

    Comparing small sample to large population using ANOVA

    Hi, I have a problem I was hoping to get some help with. I am trying to evaluate the impact of an after school program on GPA, Discipline offenses, and attendance for a school district. The district has provided me with the quarterly data for each of the DVs, as well as whether or not a...
  14. P

    How does sampling reduce selection bias?

    Hi everyone, I'm struggling to understand theoretically how sampling reduces selection bias. Take the following example: Supposing there is a population of 1000 people, and 200 of them have an axe to grind (for some reason). These 200 will respond to 100% of surveys. The remaining 800 are...
  15. A

    Really Basic A level Statistics Test. (Multiple Choice)

    1) ‘Cluster sampling’ is a term given to one method of (a) Selecting random numbers using excel (b) Probabilistic sample selection (c) Snowballing (d) Downloading secondary data (e) Selecting a population 2) ‘Stratified sampling’ may provide greater precision of population...
  16. B

    simple question about sample randomness

    Thanks for looking at this. I've been given a sample of data of 105 cars. Our teacher didn't specify whether or not the sample is random, but most of the hypothesis tests I'm to perform require a random sample. I thought I could get around the possible non-randomness of the sample by taking...
  17. R

    Increasing sample size with a second sample?

    This is not a homework question but I think it is an elementary question: Say I have a simple random sample (without replacement) of 50 items from 500. Now I decided I want to increase my sample size to 60 items. I know that I can use my original seed number to generate a sample of 60 where...
  18. 9

    What sampling method is this?

    Hi, I hope you can help. I collected my samples on the street by just asking passers by to fill in my questionnaire. I moved to 5 different locations within the city and spent 3 hours each visit 3 times a week for one month. Is this random sampling? Or it it sill convenience sampling? Can...
  19. D

    Design effects (or variances) of sampling methods?

    Where I can find comparison of variances (or design effect) of different sampling methods? Same population, same sample size: I want to know which one has smaller variance than other; in simple random sampling, systematic sampling, stratified sampling, cluster sampling and so on.
  20. W

    sampling issue for a data set with an embedded pattern

    I have a large set of data sets. For instance, it has 30000 data points, which are identified as 1, 2, 3,…30000. For notational purposes, D(i) represents the data value for a point identified as i. These data points have the following localized pattern, For a given integer value k...