standard deviation

  1. M

    How to divide standard deviation

    Hi, I am developing a model of vehicles traveling regular routes. Assume the length of the path (distance) from each stop to the next is known. Assume the mean travel time is known from each stop on the route to the next. Further assume the standard deviation for the mean travel time from...
  2. B

    Normal Curve & Standard deviation HELP!

    This is my homework question and in my right brained mind can not or the life of me think any further. My only hope is that someone out there in the universe can help my melted brain: Pick a continuous variable (that is, interval or ratio in scale of measurement) that is normally distributed...
  3. K

    Need help interpreting Standard Error and Standard Deviation

    Hello, In another post on SPSS forum I discussed Order effects where I split file on SPSS by order and conducted an independent t test looking at the effects of group on the DV. I found that the original result was only evident in order 1 and not order 2... however on the second order one...
  4. T

    Ordinal or interval survey response analysis (from a convenience sample)

    I have the responses from a survey where people had to provide a rating on a scale from one to five, where five was most positive side of things. I would like to assume it is interval scale where the differences between each point on the scale are the same, as I would like to compute...
  5. A

    Higher standard deviation than the mean

    HI ! Excuse me for my english, my writing is not very good. I want to know what implies or what explains in an excercise when the standard deviation (STD=67) is higher than the mean (M=38), and the histogram behaves like an exponential distribution. Thanks by the way ! :tup: Regards from...
  6. T

    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...
  7. M

    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...
  8. E

    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...
  9. F

    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...
  10. M

    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...
  11. E

    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...
  12. Y

    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...
  13. P

    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...
  14. A

    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 (#...
  15. B

    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...
  16. J

    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...
  17. A

    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...
  18. P

    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...
  19. B

    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!
  20. A

    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...