standard deviation

  1. S

    How do I prove my results are statistically significant or not?

    Sorry in advance, I'm a complete statistics novice! I have a three chemical samples which were prepared in exactly the same way, and when tested have given different results. How would I statistically compare these? I was told by somebody to divide the average by the standard deviation to get...
  2. J

    Using Median and Standard Deviation in syntax

    Hi, I'm quite new to SPSS and am looking to code my data records by whether or not they are within 1 standard deviation of the median for that variable. So far I have been doing this for each variable: DO IF (HumanIL21Normalised GE -1.6336 AND HumanIL21Normalised LE 0.3664). COMPUTE...
  3. L

    Interpreting Standard Deviation

    This is the problem: The output from a statistical computer program indicates that the mean and standard deviation of a data set consisting of 200 measurements are $1,500 and $300. What can be said about the number of measurements between $900 and $2,100; between $600 and $2,400? I know the...
  4. G

    Standard deviation of a set of random odds

    Standard deviation of a set of random probabilities Imagine I have n mutually exclusive events whose probabilities are perfectly random. The sum of their probabilities is 1 of course. What is their most likely standard deviation, if there is one? Playing around with R, it looks like there is...
  5. Z

    Error on mean or standard deviation

    I have a plot which has average values on the y axis but the averages are based on only 3 samples. Should I use the standard deviation or the error on the mean for error bars? The error on the mean is obviously smaller and so looks more senible in terms of error bar size. Apologies if a...
  6. V

    Data clustering, error and closness formula lemma

    I need to know how error and closeness formulas, attached in file are formed or what is the significance of these formulas?
  7. R

    De Moivre's Equation The Most Dangerous Equation - Trial of the Pyx

    I don't understand the Trial of the Pyx example in the following (http://press.princeton.edu/chapters/s8863.pdf). De Moivre's Equation (http://math.stackexchange.com/questions/253486/name-of-de-moivres-equation) Excerpt: In 1150, a century after the Battle of Hastings, it was...
  8. S

    Hypothesis Testing for Standard Deviation

    Hello! Attempting to complete this problem: -- The observations (volume in m^3/ha) of 10 prism plots from a given forest type are summarized as follows: sample mean = 420 m^3/ha "10" on top of the ∑ and "i-1" below the sigma, with "x^2" beside it = 1,778,400 (m^3/ha)^2 Using the...
  9. J

    Which test to use?

    Thanks in advance for reading my post. I have a year's worth data that describes the frequency of patient falls organized by the attending physician. Each physician has a unique number of cases (i.e. one doc can have 40 cases, and another has 15). I want to know whether the monthly count...
  10. S

    Which statistical procedure to use (given standard deviations and means)?

    Can someone please help me with this? Which statistical procedure could I use, and how could I set this up? A company operates four machines during three shifts each day. From production records, the data in the table below were collected. At the .05 level of significance test to determine if...
  11. E

    Standard deviation of the mean difference out of Pre/Post Test Descriptive Statistics

    I have several RCT pre/post intervention studies that I am calculating Hedge's g for. All of the studies report the difference of mean and difference of standard deviation between pre/post for each group except one. I know how to calculate the difference of mean [= Mean(post)-Mean(pre)], but...
  12. X

    Find correlation when SD and mean are given

    A guy got 88 in his test which has mean score of 64 with SD 8. He missed the second exam in which the meanscore was 45 and SD was 5. He got a prorated marks of 55. The prof used regression to get his second test marks. What was the corelation between 2 exams ? P.S: I would really appreciate...
  13. K

    Standard deviation/E@R over time with changing exposure

    Hello, I need some help with this statistics/finance problem: Imagine you own an asset over four periods and the value of it is affected by market price movements. You know the standard deviation and the position that will be held during each period. To complicate the problem, these are...
  14. I

    Non-Stationary Series and Standard Deviation

    Hello I am trying to model a non-stationary series for the purpose of outlier detection. The series is not labeled as normal and abnormal, which is a part of the problem. In the first step to model it, I figured out the seasonal dynamics which were at 1 min and 60 min. You can see the AC...
  15. C

    Effect Coding: p-value of reference category

    Hi, I fit a regression model with effect coded variables. I'm well aware of how to compute the value for the reference category but I have absolutely no idea how I can possibly compute the p-value or standard deviation for it. I really hope anyone can help me in this matter.... Thank...
  16. J

    Percentage of data points in distribution

    Hello, I have a sample of data for which I have figured out that the population mean for the height of US 12-year-old children is μ = 150 cm with σ = 6 cm. The heights are normally distributed. I now need to figure out the percentage of children have heights between 141 and 159 cm. Any help is...
  17. 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...
  18. J

    Predicted standard deviation with simple linear regression

    Hey, I am working on a prediction of wind speed. I'm using two datasets, one with 10 years of data, one with 1 year. I perform a simple linear regression for the dataset for the corresponding year. After I found the slope and offset i use the long dataset to make a prediction. The prediction...
  19. D

    Standard Error - interpretation and relative standard error

    Hi, I am unclear about how to interpret the Standard Error of the Mean (SEM) directly. For example, when a mean is reported as 5.00 + 0.50SEM, how do you directly relate the 0.50 to 5.00? To help address this question I have written dot points about what I know about the SEM and interspersed...
  20. L

    Determining the Standard Deviation (vice Standard Error) of regression coefficients?

    This is a question I’ve been wondering about for a while, but perhaps it’s not possible or perhaps I just need a point in the right direction. I constructed the attached mock data samples with four variables, A, B, C, D, each of which is either present (1) or not (0). The true value for each...