sample size

  1. H

    Sampling methods, which is more appropriate?

    I have been collecting data on the temperature in an experiment for the last couple months, and I'm interested in the rate of temperate changes. The total amount of data is extremely large, and takes a long time to process, even using multi-threaded code. Currently I'm doing option 1, but I'm...
  2. A

    Distribution of a subset of the complete sample

    Dear all, My question can be easily misunderstood, so please allow me to briefly explain the experimental conditions. I have measured a variable from 120 individuals in total, 60 of one genotype and 60 of another. The distribution of the complete sample of each of the two genotypes is...
  3. M

    Why 30 as sample size?

    I've read that 30 is a good rule of thumb in most cases for an adequate sample size. Most places say that this is just an agreed upon approximation of an infinite normal distribution. Can anyone explain well why 30 is this agreed-upon number? Thanks very much...
  4. S

    sample size formula

    Hi, I have a sample size calculator problem: I have to draw a random sample of Toyota car owners from a city; I know the size of the population and i know the number of Toyota owners. What formula should I use? is it n=p(1-p)(z/E)^2 If this is correct then what is p? Is p the...
  5. A

    Why does a larger sample size produce a smaller p-value?

    Hi, I need help with this problem... The obtained p value for a correlation analysis is .036, for a sample size is 50. If the analysis had been undertaken with n = 90, and the same sample correlation value was again observed, what would be the relative size of the p value for the second...
  6. K

    Alternatives to logistic regression when the number of cases is low

    Hi All I got involved in my first foray into logistic regression, but have come to realize that I probably can't use it. Let me tell you about my data. I am investigating the consumption of 3 different insect pests by bats in an agricultural area. The response variable is binary for each...
  7. Z

    How do I calculate the Sample Size for this type of Survey?

    Hi all, I need to calculate the sample size for a survey I will be undertaking soon. The target population will be the clients of 8 hotels, forming part of the same company. The objective of the survey is to get the profile of the clients and their level of satisfaction. I've read that if the...
  8. P

    How to compare a small sample to a large control group sample?

    Hello, The prupose of my research was to measure the impact of a dropout prevention program. I used a survey consisting mostly of Likert scales and I compared the answers to a control group. The control group was relatively large, as it was based on a government study of roughly 1500...
  9. B

    Estimating sample size for reliability study

    Hello, I'm having problems calculating the required sample size for my PhD study. I have designed my first study, which is comparing moral reasoning abilities in people with a brain injury to a healthy comparison group. I have used previous similar research and G Power to estimate the...
  10. S

    [HELP REQUESTED] Calculating Sample Size Based on a Pilot Study [HELP REQUESTED]

    Good morning Talk Stats, I come to you after many hours spent on the web researching and working hard to find a solution. So far, I have been unsuccessful. Here is my situation: I am trying to calculate sample size needed for a immunohistochemical study. I have done a Pilot Sample which...
  11. 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...
  12. M

    calculate sample size for sensitivity and specificity in a new diagnositic test

    My question is difficult to me, I had read an article about how to calculate sample size the foot note tole me"" ε = required absolute precision on either side of the sensitivity "" what is the absolute precision means ? and generally how to chose required absolute precision on either...
  13. J

    Standard Deviation not Equal to Standard Error

    Question: If the standard deviation of a particular sample with size N is not equal to the standard error for samples of the same size. Can you tell which is larger? If so, why? Choices: A. Yes. The standard deviation gets smaller with increasing sample size, so it must be smaller...
  14. D

    Adding Multiple Sample Size Values to a Box plot

    Hello, I am working on a boxplot where I would like the N (sample size) to be displayed on each box and also the different number of trials that the samples came from.. I have some sample data as follows: structure(list(Female.Name = structure(c(3L, 3L, 3L, 5L, 5L, 5L, 5L, 4L, 4L...
  15. L

    Help with probability, sample mean & standard deviation

    Can anyone help me on how to do this problem? I'm so confused
  16. T

    Test of proportions; study design and sample size

    I want to look to see if there is an association between two conditions. Basically, patients come into dermatology and complain of an itch between their shoulder blades and are diagnosed with this thing called "NP". I believe the itch may be due to a muscle/skeletal imbalance hence something...
  17. victorxstc

    Contributions to writing code that enable R to analyze the "Descriptive" statistics

    Apparently R does use only the raw data. In some other statistical programs, there is the option to calculate some simple tests, only by inputting the descriptive statistics. I for one think it would be much better if we could enable R to run such tests too. There are not many tests that can...
  18. K

    How many measurements needed to distingish between two outcomes?

    I have a historical dataset of about 500 measurements. Datapoints that turned out to indicate A or B, each have a distribution from which I computed mean and std. If I plot a histogram of these measurements, I have two semi-overlapping gaussian distributions. Those measurements that indicated A...
  19. I

    Using GPower3 to calculate sample size

    I ran the following calculations in GPower3 but I am doubting my method and I am looking for suggestions but also perhaps a beginners way of checking this mathematically. I have a one way test, with an r of .25 an alpha of .05 and a power of .80, I came up with a required sample size of 95...
  20. T

    Sample size when comparing 3 groups (proportions)

    Problem: I use a common clinical specimen divided equally into two sets with each set to test 3 culture media for growth of a certain organism after processing. The 1st is processed by method A. The 2nd processed by method B. After processing, inoculation to 3 media each was done for the...