# standard deviation

1. ### displaying data

Hi everyone I have a really basic question. I am displaying mean and standard deviation as a function of time by means of a line plot with scatter point circles representing the std. I am doing this for a number of different systems on the same graph so that they can be easily compared...
2. ### Standard Deviation of a Sequence of Standard Deviations

Hi, My goal is to estimate arrival times of buses at bus stops where historical GPS data for each bus is available and real-time bus location is available for each bus. What I would like to do is use the historical data to determine the mean time (in seconds) and SD taken for a bus to travel...
3. ### Standard Deviation of Mean Absolute Error

Hi guys, As basic as this question is, I'm looking for a way to calculate standard deviation of mean absolute error using pivot table or atleast using excel. I have fitted and predicted values. I calculated abs(y-yhat). and then when i used pivot tables i used "average" value to be...
4. ### Basic question: is the std of complex numbers the std of its components?

Sorry for the basic question, I searched the internet but could not get a simple and clear answer. Application: I want to compute the std of a direction / bearing , values are from 0-360. I can convert the values into complex numbers and back to have a proper average. Question: Can I...
5. ### The z-scores of the 68-95-99.7 rule aren't matching up with the values in my z-table

The z-scores from the 68-95-99.7 rule, which are 1, 1.96 (or 2), and 3 according to my textbook, arent matching up with the values i get if i try to find them using the Z-table in the appendix of the textbook. For example, the rule says 95% of the normal distribution falls within 1.96-2 std...
6. ### STATA - Finance - Portfolio Volatility

Hi all, I am experiencing difficulties to calculate portfolio volatility each period ("rebalance") given the following variables (enclosed). Correlation ("corr_Nt") across assets ("ticker") remains constant within a period. It is an equally weighted portfolio but weight changes each period (#...
7. ### statistically analyse pass rate of test in different locations

I'm looking to analyse some data and as it's been a long time since my statistics days I'd like to know which area of statistics my problem lies. Lets say I have a number of different driving schools, each doing the same test of their student drivers' ability to have a licence. Now every...
8. ### calculating probability of disease according to age

I'm making a program which, at one point, is supposed to estimate the probability of having a certain disease based on the patient's age. I'm going to feed the mean age at which the disease occurs, along with the standard deviation, into the program, but I can't figure out how to actually...
9. ### 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...
10. ### 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...
11. ### 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!
12. ### 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...
13. ### 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...
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### 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?
20. ### 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...