normal distribution

  1. G

    How can you prove normal distribution enough to use e.g. ANOVA not Kruskal Wallis?

    Hi everyone, I'm trying to produce an automated framework for choosing hypothesis tests and carrying them out. I really am new to statistics so sorry if I'm asking really obvious questions, but I've tried for so long to find an answer and aren't getting anywhere. This also isn't homework help...
  2. B

    Sum of n random variables with normal distribution

    I am struggling with this problem: Independent random variables X_1, ... , X_n have normal distribution with mean 0 and variance 2. What is the distribution of random variable: X_1 + ... + X_n ? I know that the sum od two random variables with normal distribution has normal distribution as...
  3. S

    Seemingly unsolvable conditional probability

    The following is a question that is likely to be appear on my exam on Friday (tomorrow) but contextualised into a different scenario. I'm having serious difficulty figuring out how to go about answering it. If anybody has encountered something similar and could provide a step by step explanation...
  4. R

    Finding the Z-Score for Safety Stock Calculations

    Dear Forum, I want to calculate the safety stocks required by our company to achieve a certain service level for our customers. The basic literature around this topic is quite clear: • Find the Standard Deviation of the Demand (expressed in weeks of demand in my case) • Define the service...
  5. S

    Justify the use of parametric tests on non normally distributed data

    Hello there. I have 5 Likert scale questionnaires that have been answered by the same people who have been randomly selected (N=24) and i have the following problem: I first test the data distribution of each scale in order to determine what statistical analysis tests should i employ...
  6. C

    Goodness of fit test for a normal ditribution

    In the example from a site I was trying out http://www.cimt.plymouth.ac.uk/projects/mepres/alevel/fstats_ch5.pdf this problem in page 107 about Goodness of fit test for a normal distribution.Question is about analysis of fat content of hambergers. I understand that we need to have the two...
  7. A

    Help for student

    hi, I have a question, as how can we analyse the relationship between the dependency and normal distribution data in STATA.
  8. A

    Solution for Non-normally distributed data

    hello there, I am doing some statistical analysis on medical sample data. I need to need to find variables which influences the length of stay in hospital. I was panning to do collaboration analysis and stepwise model for detecting regression model. My data is nor normally distributed...
  9. C

    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...
  10. S

    Comparing groups - which test should I use

    My study is to assess the mental state of elderly patients, one of the objectives is to compare the mini-mental categories, which is an instrument that measures the level of cognition of classifying subjects into 4 categories: normal, pathological suspicion, deterioration and dementia, but I...
  11. P

    QQ plots

    Hello! This is the first time I post to the forum. I'm a numismatist working with ancient Greek coins. I'm trying to examine the normal distribution of the databases I created: c. 25,000 coins. For this reasons, I QQ plotted coins from my main database (c. 8,200 coins) versus those from...
  12. C

    Unbiased Estimator.

    the radius of a circle is measured with an error of measurement which is distributed normal with mean 0 and variance \sigma^2,\sigma^2 unknown.Given n independent measurements of the radius , find an unbiased estimator of the area of the circle. By using *Maximum Likelihood Estimator* I found...
  13. S

    Normal Distribution

    I cant figure out how to do this problem: I have 2 sets of means and 2 sets of SD 1sth graders scored a mean of 25 and a sd of 5 5th graders scored a mean of 30 and an sd of 10; assume the distributions are normal How do i figure out what percentage of the first graders scored better...
  14. P

    data transformation- varied result using log10- better method?

    To transform or not to transform and how to transform data? Hi, My study: - 2 groups- 1. Not allowed to work; 2. Allowed to work (control) - compare the groups on various aspects like quality of life, depression, anxiety, etc on standardized quantitative questionnaires - compare if coping...
  15. L

    Normal probability question help

    Hello Statisticians! I would really really appreciate any help with this question: Q. The grade a student receives in an exam is given my a normal distribution with mean 3.5 and variance 1/16. 1. Find the probability the the student scores between 3.4 and 3.6 for an individual course...
  16. K

    SPSS - Kolomogorov-Smirnov Test

    I am a masters student and I am trying to assess which tests to use. I am checking for normal distribution. I have conducted a Kolomogorov-Smirnov test by going into descriptives>explore>plots>check for normality. I was given a value for 0.000. However I also conducted a Kolomogorov-Smirnov...
  17. J

    What will be the transformation and Jacobian of transformation for the following case

    Let X_i\sim N(\mu_i,\sigma^2) ; where [i=1,2,\ldots,n] show that \bar X and (X_i-\bar X) are independent. If all X_i had same mean \mu then we transform the random variables X_i; [i=1,2,\ldots,n] to Y_1=\bar X Y_2 =X_2-\bar X Y_3 = X_3-\bar X \vdots Y_n = X_n-\bar X...
  18. W

    Appropriate tests for comparing 2 normally distributed datasets (ttest?)

    Hello, It's been a while since my A-level statistics course so I just want to make sure I'm doing the appropriate test for my data. I'm a PhD student working in X-ray crystallography. My situation is that I have 2 populations of data, of varying sizes, in one population the samples have...
  19. B

    Z-scores with non-normal data

    Hi, I am reviewing someone's study in which they used z-scores to standardize and compare data. I see no mention of their test for normality and when I looked at their raw data, I found much of it to be heavily skewed and not-normally distributed. I need to determine whether this means...
  20. F

    Normally distributed RVs

    Hello. I'd like to know how can I calculate the probability that normally distributed random variables locate on the surface area on a cylinder? I thought about it myself and I came to multivariate (trivariate) normal distribution.But I'm not sure. Thank you in advance