normal distribution

  1. D

    Normal and non-parametric repeated test data

    Hi All I have done some experimental work and collected data for the conductivity of water with various concentrations of salt. The experiment collected data every 15 mins for 24 hours. Some of the data produced is Normal and other data sets are not normal. Hence I don't know what stats I...
  2. R

    Finding two unknown Z's...

    Hi! I have two problems in which I have to find the unknown Z or X... I've really done well with this section but somehow I just can't remember how to do this and am worried it'll be on the test. Can anyone point me in the right direction/give me the first step? 1. Find Z so that...
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    if z-value is a negative number, how can i calculate the Probability?

    Hello guys, :) I have an important question I want to ask. I have already searched the web and my statistics book but I can not find the answer :( I stumbled across this problem when preparing for my final from statistics and I can not figure out how we can get P=1 from a z-value=-10.6066...
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    Finding a UMVUE for variance of normal distribution

    Let Let X_1,X_2,...,X_n be a random sample from a normal distribution with mean \mu and variance \sigma^2 . I showed that (\bar X,S^2) is jointly sufficient for estimating ( \mu , \sigma^2 ) where \bar X is the sample mean and S^2 is the sample variance. Then assuming that (\bar...
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    Help with the normal distribution using R

    Hi! We are total statistics and R-newbies, and we're having some difficulties with our data that we hope some of you might be able to help us with. The problem is that we don't know how to check if our data is normally distributed/we don't know how to make it look normally distributed...
  6. A

    Have population, use inferential stats? Non-normal dependent variable, what to do?

    Statistics people! I have two questions for you. I am NOT a statistician so please be nice and answer simply :) Background: We are looking at parental leave in Iceland. We are particularly interested in whether the economic crisis and the resulting changes in parental leave legislation...
  7. D

    Normal distribution with Mean Absolute Deviation What percent lies within 1,2 AbsDev

    Roughly 95% of the normal distribution lies within 2 standard deviations. However, recently I have begun using the mean absolute deviation a lot. What percent of the normal distribution is within 2 mean absolute deviations? Is this possible to calculate?
  8. S

    Confidence of Distribution

    Hi all, say I have a known normal distribution, which was created by an experiment. Now, I take another measurement, one only, and assume this is the mean of my new distribution, with similar properties as the known distribution. How can I calculate, how sure I am that this new distribution...
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    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...
  10. 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...
  11. 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...
  12. 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...
  13. 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...
  14. 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...
  15. 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.
  16. 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...
  17. 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...
  18. 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...
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    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...
  20. 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...