1. L

    Accuracy of a transformation of a data set

    Hello, I'm very new to statistics and ran into a problem that I don't know the answer to. I want to do a capability analysis, but my data set is not normally distributed, so I transformed it using the Johnson transform in Minitab. Now I had a normal distribution and very good CP, CPK values...
  2. U

    How to interpret Weibull Accelerated Failure Time (AFT)

    Hello, I fitted a Weibull Accelerated Failure Time (AFT) to my dataset (n=1071). The output reported the shape parameter (B=0.67,p<0.001). My understanding is that since the coefficient is less than 1, this means that the hazard is increasing over time. Is this correct? I also fitted another...
  3. P

    Time shift with distribution

    Hello, I'm looking for a formula that accounts for a timeshift that is distributed (weibull/lognormal) For example. I have "hits" that fall into a week. W1: 1 1 1 1 1 1 Total hits W1=6 W2: 1 1 1 1 Total hits W2=4 W3: 1 1 1 1 1 Total hits W3=5 W4: 1 1 1 1 1 1 1 Total hits W4=7 Each week is...
  4. S

    Statistics for market analysis

    Hello there First of all I am not a pure statistician, however I worked with Weibull stats during my PhD. Now that I am working in marketing, I realized that "customers' orders" can be modeled with Weibull (someone can argue: what can't be modeled with Weibull?!?... Weibull is life!). In...
  5. P

    Applying the Weibull equation to fit data to a psychometric curve

    Hello, I would be very grateful if someone could tell me if my application of the Weibull function to my data is correct or not. (The question is very simple, but requires a bit of background information, so please bear with me!) Please find below a few background details about my study: - I...
  6. Y

    Why are the parameters of weibull not unique for a given data ?

    I have a data which is the interval days of customers purchasing products. I try to estimate the shape and scale params by scipy.stat.weibull_min But, the parameters returned from the fit function is not unique and when I try to constrain the scale param to be 1, it does not work. Here is the...
  7. M

    Raw moments of 3-parameter Weibull distribution

    Hi, I know that the formula for computing the raw moments of 2-parameter Weibull distribution is: Mu'n=b^n*Gamma(1+n/c), where b and c are scale and shape parameters, respectively. However, I couldn't find any exact formula for a 3-parameter Weibull distribution. Is there any simple formula...
  8. C

    Root mean square error

    I have got a set of wind speed data for weibull analysis. And I need to calculate root mean square error (RMSE) for statistical test.How do I calculate it?
  9. I

    Parameter estimation

    I am doing project in which I need to estimate weibull parameters for car part failures ( I know data follows weibull ). I have 1000 cars data (part failure data). Now the problem is suppose some part fails after 6 year( from date of manufacturing) . But i have data of only first three year. Now...
  10. K

    Difference powerlaw, lognormal and streteched exponential (Weibull) function

    I am currently fitting above mentioned functions to my data and I can observe, that both lognormal and Weibull are better fits than powerlaw. In literature, it is often suggested, that it is hard to distinguish these functions, but I can in my data. I do not completely understand the...
  11. V

    Weibull distribution for data with zero's

    Hi, Can any one tell me how to fit some data with zero's to a weibull fit using Matlab. I tried using Maximum Likelihood Estimator and wbfit. But I am experiencing problem because of zero's. It requires positive values. Thank you very much Vinay
  12. J

    Changing the units changes the scale and shape of Weibull pdf?

    Please delete this post I don't know how to delete the post.:(
  13. M

    Life data analysis zero time failures problem

    Hi, I have life data which contains time to failures of zero, I'm really not sure which distribution I should use to analyse this data, i've tried using a weibull distribution in software such as mintab and Weibull++ but they either ignore the data when calculating the parameters or do not...
  14. G


    I was wondering what methods you can use if you are trying to predict failure in a product. I have a product and the following information about the product: 1. The date it was produced 2. number of products produced in the lot 3. The number of products purchased out of that lot 4...
  15. G

    Life Data Analysis

    Good Morning, This is the first time that I have posted anything and I am really in need of guidance. I am trying to figure out the best way to predict failure using warranty data. I have a product that had very few claims in the beginning, but the longer the life of the product the...
  16. R

    weibull for free form data (interval)

    How do i implement lifereg or generate a weibull distribution for this kind of data? Time (Mins) Cumulative % Failure 0-30 4 30-60 10 60-90 15 90-120 18 120-150 22 150-180...