poisson

  1. R

    Comparing means with Poisson distributed data?

    Hi everyone! How can I perform ANOVA, so to compare means, when the data of my groups are clearly Poisson distributed (towards 0 values)? Thanks a lot! Cheers
  2. N

    Propagation of Poisson Errors

    How do I combine the asymmetrical errors when I subtract my samples from the controls? I know my low counts follow a Poisson distribution and therefor I cannot simply add in quadrature as per Gaussian errors. Thanks in advance, N
  3. noetsi

    Comparing data to a theoretical discrete distribution

    With continuous data you can test if your data meets a theoretical distribution with a QQ plot. However, SAS won't generate these for discrete distributions such as Poisson (with good reason as the author notes in the link below as the results are dubious for such a distribution). The author...
  4. N

    proc genmod/inverse gaussian

    Hello everyone, By estimating the count data (number of claims per insured) with an inverse Gaussian distribution by the GENMOD procedure SAS, SAS does not take the zero (0) data. Indeed for the dependent variable (number of claims) many contract have a number of claims 0. when I execute...
  5. N

    Correct measure of central tendency for Skewed distribution

    Dear Talk Stats users, I am trying to solve following problem. I've got a data, which has a skewed distriubution (see attachment ) Now I can not find, how to interprate correctly the central tendency of this kind of data, because, probably this type of distribution is specific or I can't...
  6. C

    Poisson distribution and muon decays

    Hello, I have gathered muon decay data and used R's non linear least squares function to find the mean muon lifetime. I did this by taking the exponential part of the decay curve and solving for the inverse of the lifetime, where the function is Nt=N0(exp(-t/τ)+c. That bit is fine. The...
  7. F

    Interpretating poisson regression output correctly to wirte in results from R

    Hi. I've done a poisson regression on count data in r. I need to write up the results for it but have very little idea where to start because the p value shown are linked to the other variables. I've searched online and thought I was getting somewhere but I've seen so many contradictory...
  8. H

    Fit of generalized linear model (Poisson distribution)

    Hi guys Can anyone tell us how to evaluate the fit of our generalized linear model with a poisson distribution? We can't really tell if the model is a good fit or not. Do you use the deviance to answer this question? If so, what does it tell us in the following example? Thank you in advance...
  9. R

    [HOMEWORK-USING R] Poisson Model using likelihood

    Question :A well-known example involving the Poisson model was described by LJ Bortkiewickz (1868-1931). The data refer to the annual number of deaths by horse kicks in battalions of army soldiers. Fourteen battalions were examined over number of years, resulting in a total of 200...
  10. F

    Weird PQML coefficient values (compared to GLS/OLS output)

    Hi all, first and foremost, any help for my little issue here is much appreciated! I am currently writing my master thesis, where I'm analyzing common currency effects on trade flows. Therefore, I'm using the Gravity Model of Trade for it. After conducting a first OLS regression with rather...
  11. H

    Events following Poisson Distribution including a fixed dead time

    Hi, Im trying to describe some events with the Poisson distribution and overall its a really good fit. There is however a slight error in the model since there is a dead time when every event is about to happen. Imagine for instance taking a picture with an oldfashioned polaroid camera...
  12. J

    poisson regression (Offset or not)

    Here is the problem and my question: A group of 250 pediatric patients with hydrocephalus who had received a ventriculoperitoneal shunt (VP) was asked at a routine neurosurgical follow-up visit to recall the number of days over the last month on which they had at least one headache...
  13. S

    I Need Help with Poisson Distribution Problem!!

    I don't know where to even start with this Poisson Dist. problem, can anyone help me solve this??? The Hillel Sandwich Shop specializes in delivery of sandwiches in New York's financial district. Customers phone or fax Hillel their orders, which are then delivered directly to the customer's...
  14. N

    Restricting the Poisson distribution pdf

    Hi All, I have a question about using the Poisson distribution. Say I want to model the counting of events, anything, I don't care what. Let's just say the number of items of mail the postman brings per day. Over time I measure this and find the average, to be 3. I can then obtain a...
  15. D

    Which statistic should I use for rare events?

    Hello all! I want to estimate the mean prevalence out of a number of studies (8 retrospective cohorts). The sample size in all studies is large N>4000 and the probability of the event small p<1%. Should I use the binomial or the Poisson distribution to estimate the 95% confidence intervals of...
  16. J

    Poisson Model Help

    Hi everyone, I am having a hard time finding my lambda for this homework question. I know something has to be multiplied to get it into the same units and that lambda has to be an average. However all the information I am given is an average. If you could help me that would be great!! Here...
  17. P

    Confidence intervals for difference between Poisson rates

    Hi, My data consists of occurrences of words in time windows. E.g.: Day; Word; Frequency 1; "dog"; 45 1; "cat"; 2 ... 2; "dog"; 90 2; "cat"; 4 ... I would like to estimate the ratio of day-to-day difference (i.e. for dog: 90-45/45 = 100%). For cat the increase is also 100%, but due to...
  18. P

    [SaTScan] relative risk confidence interval calculation

    Thank you for reading this. My question is regards the methodology used by SatScan for purely temporal cluster analysis using a discrete Poisson model satScan's output gives me the following: How do I calculate confidence intervals around the relative risk? Thank you!
  19. S

    Is normal dist OK for these count data?

    Hello, I am modelling some count data (ANCOVA). I use R for statistical computing. I am not sure if I must use a glm with poisson errors. There are 120 counts in 4 groups and only one zero count. The maximum count is 12. The median is about 4 and the distribution of...
  20. C

    Histogram PDF fitting- Bin Variance Poisson or not

    So my basic query is just because you've binned and counted the data into a histogram are the error bars on the bins necessarily the Poisson sqrt(N)? Longer explanation: I have an image of pixel values which represent brightness values. Im binning them into a histogram to get the PDF of the...