normal distribution

  1. S

    CLT Chi squared and negativity

    A variable with the number of degrees of freedom reaching infinity has a distribution coinciding with normal distribution (as CLT). On the other hand, this variable cannot take negative values. How to explain it? Is there an assumption in CLT that it can be used for positive values only?
  2. S

    Finding sample mean for normal distribution

    Hello friends, I require help on the below question on normal distribution. "An e-commerce company tries to settle the customer complaints on refund within 5 days. If a refund is not processed within 5 days, then the company has to provide coupons for Rs.500 to the customer. If the company...
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    CI from normal distribution using indicator random variables

    Suppose that {X_1,X_2,...,X_n} is a random sample from N(m,1). Let I_i be indicator random variables such that it is 1 if X_i <= 0 and 0 otherwise. Calculate the 95% confidence interval for m. Suppose that sample is large enough.
  4. A

    Z Table Rookie Question

    We've been told to find critical value that corresponds to 80% confidence level. I dropped 10% from each tail since it's symmetric. Am I right in proceeding by finding where 0.90 is in the table to find out the right limit and then minus that to find the left-end point hoping it leaves 80% in...
  5. M

    What is the Confidence interval of this...?

    HI Friends, I've attached excel sheet having 19 records. Can you guys pls help me in finding 95% confidence interval for this. I tried finding it all way, but I'm not getting correct answer. Should t- distribution or Normal distribution be used..? I Thank in advance. Pls help me in finding...
  6. J

    Calculation of overall ranking from mean, SD, and Z score

    Hey everyone, I was hoping someone could help me. Im applying for a job, and am trying to work out my overall ranking in two seperate exams so that I can include this in the application. Could someone please tell me if my calculation is correct? I have attached the file with my calculation...
  7. S

    Extrapolation - Getting info of a population from a sample

    Hello, I'm working on a problem where I have 30% of a full dataset and I have to estimate the generalization error. To be more precise, let's say I have the information of the transactions of the clients of a bank which has 30% of the countries market. I can easily get the mean, standard...
  8. L

    Comparing one normal and one skewed group

    Dear Forum, I have 2 groups for which I need to compare the length of stay (LOS) post-op: a control and a treatment group. My control group has the following descriptive stats: (n=66; Mean = 8.42; Median = 6.00; SD = 7.45; Kurtosis = 17.66; Skewness = 3.81), while my treatment group is as...
  9. R

    Normal Distribution of multiple Std.Dev´s and Means

    Is there a way to calculate the Normal Distribution of a set of multiple Standard Deviations (SD) and Means (µ)? I am afraid I do no have Access to the raw data from which the SD´s and µ´s were calculated. Many thanks in advance
  10. I

    I need a push in the right direction, not sure how to attack the problems..

    Hi :) I am new here on the forum and find it a bit difficult to learn the way to go at different statistics/probability - problems. For the most times I am able to figure it out myself doing some research, but the last two problems has got me stuck for a few days. I would be really thankful for...
  11. A

    Entrance exam cutoff calculation

    Last month I appeared for the phase II of a nationalized bank exam. I would like to know the effect of sample size on the cutoff score. Unlike Phase II, candidates required for Phase III are same for both years. Phase I exam is easier than Phase II. Assume the difficulty level in each phase for...
  12. E

    How to create a subset with a normal distribution

    Hello, I have a presumably easy question for you, but I am a real newbie in statistics, so please be patient. I have a data set containing N values that more or less follows a normal distribution. I need to select N/10 values among them, creating a subset with the same distribution. How can I...
  13. J

    normal distribution

    Hi everyone! I have a question about the answer of question 19a and e. question a: Find the probability that X is greater than 60. Why do they do 0,5 -0,3944 and not 1 - ...? Question e was: the probability is 0,05 that X is in the symmetric interval about the mean between which two numbers...
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    programme evaluation: normal approximation to binomial

    Housing first is an approach to reducing homelessness. Supposedly, it has 80 percent success rate, which means that on average 80 percent of programme participants tend to retain their housing, and not fall back to homelessness. It is also said that to reliably evaluate the effectiveness of...
  15. D

    Choosing prior for the regression coefficients in the logistic regression

    I'm trying to model Bayesian logistic regression model (using JAGS in R) with my dependent variable (status: 0=alive, 1 death) & independent variable (age) in the categorical form (0=patients < 65 yrs old, 1=patients >=65 yrs old). I'm using normal dist. as a prior for constant term, b0 and...
  16. S

    Does frequency distribution matter when using nominal/ordinal data?

    I want to do relationship analysis between different variables from questionnaire results that I've just collected and I've recently learned that you need to make sure certain assumptions are fulfilled before using certain analysis tools such as needing to have a normal distribution for your...
  17. F

    Exercise on standard distribution

    Hello, Suppose I want to calculate the probability for a user to pass from a basic to a premium account within the end of Q1 (i.e. end of march). I know that this is distributed with mean=50 days and st.dev=10 days, then the probability that a user pass to a premium account within the end of...
  18. C

    Doing Parametric Tests without normal distribution

    Hello everyone! Is it true that when your sample is more than 30 people, you can do parametric tests, even though your sample may not follow the normal distribution? In my research I have 400 people as a sample, not following normal distribution and someone told me that I can do parametric...
  19. M

    Help with normal distribution

    Hello friends of the forum I have the following doubt ... If I have a sample of only 24 discrete data, how can I prove that these data follow a normal distribution? When I enter the data into a specialized software, the software tells me that the sample fits a normal distribution, but I'm...
  20. A

    Which test should I use for two unequal groups ?

    Hi all! I have data that include 20 samples divided into 2 groups (category A and category B). The groups are independent, none of the value in one group repeat in other. N(A) =14, N(B) = 6. here is the data: category A category B 0.0119888167559 0.023185483871...