# sampling

1. P

### sampling methods - randomness sometimes a challenge

Hi everyone, I need your advice about a sampling method that might work in this quite specific context. The story goes.. I need to conduct a survey in local fruit markets in Africa. Most of the fruit marketplaces are street markets and I cannot gather a list of all the people that trade in...
2. ### Sampling for rare events

I am trying to estimate the event rate in a population where the event by definition (Money laundering ) is rare by drawing a representative sample. Assuming an event rate of 1 %, I calculated the sample size to estimate the event rate in the population using the general sample size calculation...
3. ### Computing sample size and Best Critical Region

Let X_1,X_2,\ldots,X_n denote a random sample from a normal distribution N(\theta,100). Show that C=[(x_1,x_2,\ldots,x_n):c\leq \bar x=\frac{\sum_1^n x_i}{n}] is a best critical region for testing H_o:\theta=75 against H_1:\theta=78. Find n and c so that...
4. ### 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...
5. ### 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...
6. ### 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...
7. ### 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...
8. ### 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...
9. ### 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...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### 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...
14. ### 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?
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### 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...
20. ### 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...