# standard deviation

1. ### Covariance of two products

Covariance of two products I am in a stats class and the professor has asked us to calculate the covariance and the standard deviation of the total revenue. I was given the below information: X Unit Price = $10 E[X] = 10,000 Var(X) = 1,000,000 Y Unit Price =$5 E[Y] = 7,000...
2. ### Estimating error

I have reports based on long GPS occupations of the same site, which returns X Y and Z coordinates as well as the SD for each. I want the most accurate coordinates for the point as well as an estimate of the error/uncertainty. Attached are the XYZ and SD for 8 different reports of the same...
3. ### Why are these statements false?

Hello, I was doing a practice test and I got two questions wrong. The answer key said that these two statements were false: As sample size increases, the standard deviation of the sampling distribution and the standard deviation of the population are increasingly similar. -and- For the...
4. ### 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...
5. ### 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...
6. ### 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...
7. ### 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...
8. ### 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...
9. ### 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 (#...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### 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...
14. ### 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!
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### 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...
20. ### 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...