normal distribution

  1. 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
  2. S

    Measuring the presence of a correlation

    1. Given a frequency data set (collected from 10 users by letting them watch certain videos and asking some questions about the videos) how do I determine any correlation between two variables (`Correctly guessed` and `Correctly memorized`) and calculate the significance level? Video...
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    Calculating the average variance of several normal distributed variables

    Hi, I have the following problem. I'm trying to average several normal distributed variables. To make it more easy, I'm using z-scores. The mean of the average is (Mx1 + Mx2 + Mx3)/3, in this case 0. But how do you calculate the variance? If I assume they are independent, am I...
  4. F

    Plotting a normal distribution curve over a histogram

    I'm trying to plot a normal distribution curve over my histogram but I can't get my code to work for the curve. It just looks like it's plotting a very low curve, what am I doing wrong? This is my code: minutes<-c(107, 116, 127, 126, 111, 90, 125, 124, 92, 121, 131, 137, 95, 101, 101, 111...
  5. S

    Applying Normal Distribution

    So here is the question followed by what the steps I took to solve it. Please let me know if I have done this correctly: Question: The time needed to complete an exam in a particular college course is normally distributed with a mean of 80 minutes and a standard deviation of 10 minutes...
  6. N

    t test or ANOVA, ? normal distribution

    I have an experiment on cancer cell lines. There are 7 cell lines. Each cell line is treated with a different concentration of the same drug. The average concentration that killed half the cells in each cell line is calculated, along with a standard deviation as follows: Cell Line //////...
  7. I

    distribution of ln(X) when X is binodal normal

    Hi everyone. I am trying to find the distribution of ln(X) when i know that X is distributed as a binodal normal distribution, in other words: X \sim p \cdot N(a,\sigma^2) + (1-p) \cdot N(b,\sigma^2) which I suppose also can be written as X \sim N( (p, 1-p) ( a, b)^T , \sigma^2)...
  8. S

    Use Normal Distribution and Chi-square distribution

    My question is as follows: If X and Y are independent random variables, X has a normal distribution with mean 2 and variance 4, and Y has a chi-square distribution with 9 degrees of freedom, then find "u" such that: P(X > 2 + u√(y) = .01 note: "√" stands for square root Anyway, I...
  9. S

    How to calculate the probability between two normal distributions?

    Using the normal distribution. Let X  N(1, 2) and Y  N(2, 3) where N(μ, variance) denotes the normal distribution with mean μ and variance . X and Y are independent. Let U = 2X + 3Y . What is the mean of U? What is the variance of U? What is P(6<=U<=7.5)? What is P(X>Y)?
  10. S

    Confidence Intervals for Pairwise Independant Normally Distributed Samples

    Good day, I have been thinking over this exercize for a couple of hours now and I have trouble finding a starting point. Suppose that X1,i iid∼ N(µ1, σ²), X2,i iid ∼ N(µ2, σ²), that the samples are pairwise independent, and that σ is known. Derive a 1 − α confidence interval for µD = µ1 − µ2 I...
  11. N

    t-test on percentage

    Hi all, Pretty simple question: I have two mean performance scores in percent, one is 70% +/- 3(SEM) and one is 95% +/- 1. Someone said I shouldn't do a t-test to compare these since data can't be normally distributed. Is that true? How would I compare these means then? thanks!
  12. U

    Normal distribution theoretical moments

    how we can show that the follwoing equility holds E[(x-\mu)\sigma]=0 E[(x-\mu)^2\sigma^2-1]=0 E[(x-\mu)^3\sigma^3]=0 E[(x-\mu)^4\sigma^4-3]=0
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    Standardizing a normal variable

    I am trying to understand the binomial distribution, normal distribution and standard normal distribution using the attached excel file. The example in use is calculating the distribution of a random variable X which is equal to k successful shots out of n trials in basket ball. The...
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    Test whether the SD of multiple normal distributions differs between two genes

    Hi, I am comparing data on gene expression between two different genes that have been tagged with GFP. Gene expression is measured using flow cytometry so that gene expression is a continuous variable along the x-axis, with counts on the y-axis. For each gene I thus have a normal distribution...
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    area under curve normal distribution

    Two issues, that I am confused about after reading statistics books. Example: weight of an adult is normally distributed with mean of 180 lbs and std dev of 20 lbs. 1) is the area under the curve equal to 100% or would the area be equal to the mean? The descriptions I see in statistics...
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    Combining standard deviation/normal distribution (do I have this right?)

    I have a variable with a mean of 52% and a standard deviation of 2.5%. However, the 52% mean was derived from an opinion poll which itself has a 3% margin of error, which I take to imply a standard deviation of 1.53%. Assuming a normal distribution I can calculate from the former a 21% chance of...
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    Case control, lot of parameters, N and n-Normal dist. Which test and data expression?

    Firstly, my english are not so good, sorry. I will be very happy if someone help me. I am doing a case-control study, people with and without schistosomiasis. How may I perform the Kolmogorov-Smirnov test, my groups must be together or not? I think that they must stay together. Then, I...
  18. M

    Correlation between normal and exponential

    Can anybody give me some pointers to how to compute confidence intervals for Pearson correlation in the case (X,Y) where X is normal and Y is exponential? I cannot find it anywhere (usually just bivariate normal) - and I guess that this case is common enough to be described somewhere!
  19. D

    Using ANOVA for comparing perceived emotions in reaction to an embodied agent

    Hi there, I stumbled upon an interesting paper on "The Influence of Emotions in Embodied Agents on Human Decision-Making" by de Melo, Carnevale & Gratch. Basically they ran and experiment where they used different versions of an embodied agent (a cooperative vs. an individualistic agent) in a...
  20. S

    Normal distribution

    Hi, I am working with a microarray dataset. The database contain values on 208 probes for 58 subjects. The readouts for each probe is an arbitrary unit from 0 to 5000, according to the intensity of fluorescent light detected by the slide reader. I log-10 transformed the data. Now, I am...