# standard deviation

1. ### How to plot non-parametric data with multiple time points?

Hello, I analyzed some physiologic data (blood electrolyte levels etc) which was fairly skewed, so I used Kruskal-Wallis to test for differences between groups. I originally plotted the mean and SD, but I learned that plotting the median is more suitable with skewed data. My question is...
2. ### Standard deviation of relative values

Hi! I have 5 datasets each for 20 subjects which I have to plot relative to a baseline. To be more specific: Dataset 1: Contains mean value of the baseline condition Dataset 2-5: Contain each mean value of the conditions 2-5 Since this is the way I have to analyze these data, this is not...
3. ### Determine standard deviation from percentages

I have a normal distribution of data with a mean of 0. I know that 80% of the data falls within 3 units of the mean. So 80% of the data is from -3 to 3. How do I figure out the standard deviation? It's been a couple decades since my last math class and I'm forgetting this stuff. Thanks!
4. ### statistics question re margin of error, standard deviation

I took a test for which the score range was 70-130. A score of 100 represents the average score of my peer group. The standard deviation was 15. My score was 105. I am wondering how accurate the test is, i.e. would a score of 100 in a hypothetical perfectly devised test be truly anywhere...
5. ### Standard deviation of difference of means

Hi, I am sorry of this stupid question :confused: I would like to know if it possible to calculate the standard deviation of a difference of means, having the two primary standard deviation and the two primary sample size and the two primary means. For example: I have 24 men that at T0...
6. ### 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...
7. ### 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...
8. ### 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...
9. ### 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...
10. ### 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...
11. ### 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?
12. ### 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...
13. ### 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...
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### 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...
20. ### 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...