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Forum: Biostatistics

Epidemiology and biostatistics, public health research. GLM, logistic regression, survival analysis, clinical trials.

  1. Correct statistical design for Xray study

    Hi all, I'm putting together a simple study looking at two different xray programs and whether they affect clinical decision making for...

    Started by Korbah‎, 12-10-2012 07:58 AM
    • Replies: 12
    • Views: 3,067
    01-01-2013, 05:38 AM Go to last post
  2. Aic & bic

    Hello I have a little question. I have learned that we use AIC and BIC to compare models and to choose the best model to fit our data. I learned...

    Started by WeeG‎, 12-29-2012 04:15 PM
    • Replies: 2
    • Views: 2,785
    12-30-2012, 01:30 AM Go to last post
  3. Question Comparing two groups for retrospective study, what should be the sample size?

    The specific aim of the project is to compare the success rate of Indirect Pulp Therapy (IPT) and Stainless Steel Crown (SSC) vs. formocresol...

    Started by ykp614‎, 12-25-2012 07:36 PM
    • Replies: 1
    • Views: 2,353
    12-27-2012, 09:41 AM Go to last post
  4. Generalized mixed models

    Hello I have 2 questions regarding a generalized mixed model with a cumulative logit function. I had an ordinal response with 6 levels (0-5), one...

    Started by NN_STAT‎, 12-16-2012 06:15 AM
    • Replies: 4
    • Views: 2,246
    12-25-2012, 04:46 PM Go to last post
  5. Problems interpreting kaplan-meier stats and cox-regression model

    Hi, I'm working on a project. Here is my output table for an analysis I have run. It looks at a time to failure for a medical treatment. I wish to...

    Started by Stato‎, 12-14-2012 06:52 AM
    • Replies: 5
    • Views: 3,232
    12-16-2012, 11:46 AM Go to last post
  6. Should I use Tukey-Kramer or Fisher's LSD post hoc test to follow up my 1-Way ANOVA?

    Dear forum members, As part of a wildlife monitoring study, I ran 1-Way ANOVAs, where the Fixed Factor has three treatments: n1=5, n2=6, n3=5. I...

    Started by Neophyte‎, 12-13-2012 11:26 AM
    • Replies: 3
    • Views: 16,098
    12-15-2012, 01:23 PM Go to last post
  7. Using taxonomic levels as factors in random forests: does it make sense? Is it needed

    Hi all, I want to test the effect of a set of predictors (ecological and morphological factors) on a categorical response variable (an animal...

    Started by Oritteropus‎, 12-11-2012 10:30 AM
    non-independence, phylogenetic diversity, phylogenetic signal, random forest
    • Replies: 1
    • Views: 2,804
    12-11-2012, 03:36 PM Go to last post
  8. repeated measure with unequal repeats for each subject

    We want to do a repeated measure study. we have some patients who Swallow a kind of Tablet for their disease. We call this times tg-on But if their...

    Started by fatemeh91‎, 12-11-2012 07:37 AM
    • Replies: 0
    • Views: 1,566
    12-11-2012, 07:37 AM Go to last post
  9. EFA in different scales variables

    Hi I want to do an EFA with variables in different scales . for each of constructs , some of my variables has lickert scales and others are...

    Started by fatemeh91‎, 12-06-2012 09:14 AM
    • Replies: 2
    • Views: 1,829
    12-11-2012, 07:36 AM Go to last post
  10. Logistic Regression - urgent help please!

    Hello, my equation is preducting the odds of someone being male with the risk variables being smoking alcohol and using marijuana my odds...

    Started by hersheyrcl‎, 12-10-2012 02:05 PM
    • Replies: 3
    • Views: 1,864
    12-10-2012, 02:49 PM Go to last post
  11. standard curve

    Hello, I'm starting an experiment but I have several statistical doubts, and I wonder if anyone could help me. We are doing a standard curve (...

    Started by miquel‎, 12-07-2012 04:28 AM
    • Replies: 2
    • Views: 1,998
    12-07-2012, 05:28 AM Go to last post
  12. Modeling smoking in PROC GLIMMIX

    Hello there, I am trying to fit a multilevel random effect model on my data. The model looks like this: proc glimmix data=dataname initglm...

    Started by zemastear‎, 12-07-2012 05:10 AM
    • Replies: 0
    • Views: 2,781
    12-07-2012, 05:10 AM Go to last post
  13. What test to use

    Twenty individuals who have suffered a stroke are given a score on the Barthel scale. They are rated 0-100 to evaluate their ability to carry out...

    Started by alphacheese‎, 12-06-2012 05:25 PM
    • Replies: 2
    • Views: 1,795
    12-06-2012, 11:04 PM Go to last post
  14. Discrepancy between Fisher's exact test and chi2

    Hi, I'm trying to compare the absolute frequency of a disease (a) in cases and controls (b, 0 and 1). I firstly used Fisher's exact test, as my...

    Started by Mizar‎, 12-05-2012 06:20 AM
    • Replies: 4
    • Views: 2,488
    12-05-2012, 04:15 PM Go to last post
  15. Help understanding Precision (not accuracy) and Reliability

    Hello! I'm in an epidemiology class and I'm having trouble understanding how precision is judged and why it's expressed as a percent. I've taken...

    Started by lpompano‎, 12-05-2012 04:12 PM
    • Replies: 0
    • Views: 2,001
    12-05-2012, 04:12 PM Go to last post
  16. Each patient has a standard deviation, one test group and one control group. Compare?

    Hi, I need some help with a clinical trial Iam investigating. There is a Test group-T and a Control group-C T-will be trying out a...

    Started by sofiafia‎, 12-03-2012 02:03 PM
    • Replies: 3
    • Views: 2,092
    12-04-2012, 08:03 AM Go to last post
  17. A different way of presenting this data

    Hi folks, I wonder if you could help me? I'm filling in for someone at work and I'm want to express this data in a simple lay person way,...

    Started by dukduk‎, 12-04-2012 04:40 AM
    • Replies: 0
    • Views: 1,551
    12-04-2012, 04:40 AM Go to last post
  18. Urgent question about what X^2 means in testing homogeneity of odds ratios

    I did the Mantel-Haenszel Method to test homogeneity of two different contingency tables/odds ratios. The X^2 value the prof has given to compare to...

    Started by jenniferlaa‎, 12-02-2012 03:03 PM
    #contingency, #homogeneity, #hypothesis, #oddsratio, #teststatistic
    • Replies: 0
    • Views: 1,189
    12-02-2012, 03:03 PM Go to last post
  19. Poll Poll: URGENT..pls help with thesis

    Hi all, I have collected data of 100 patients who had low vision. All these patients were given a specific device and vision was noted before and...

    Started by aksh12‎, 11-30-2012 12:34 PM
    • Replies: 1
    • Views: 1,281
    12-01-2012, 04:29 AM Go to last post
  20. coefficient of variation of my samples

    hi everyone, can anybody explain me the coefficient of variation in a very simple way. What should i understand with this line in a paper "The...

    Started by poojadby‎, 11-25-2012 03:25 PM
    • Replies: 6
    • Views: 5,058
    11-30-2012, 11:42 AM Go to last post
  21. what kind of test?

    Hi all, I really need help because I do not know which statistical analysis to perform in the following case. I the following study I tried to...

    Started by ivxi‎, 08-04-2012 06:29 AM
    • Replies: 3
    • Views: 2,201
    11-30-2012, 11:09 AM Go to last post
  22. Which model to use ?

    Hello, I need some help in choosing my analysis model. I have data comparing 3 treatments (one is a new tested treatment vs. 2 common...

    Started by NN_STAT‎, 11-29-2012 06:13 AM
    • Replies: 2
    • Views: 1,336
    11-30-2012, 09:03 AM Go to last post
  23. comparison of two diagnostic tests

    Hi all, I have developed a new test named RT-PCR ELISA which has to be compared with RT-PCR taking it as gold standard. If I calculate the ...

    Started by poojadby‎, 11-23-2012 01:34 PM
    • Replies: 4
    • Views: 1,820
    11-30-2012, 08:45 AM Go to last post
  24. analysing technical and biological replicates together

    Hi everyone, I'm doing an experiment where I have 4 technical replicates and 5 sample replicates for each concentration of DNA. I want to make...

    Started by cat1082‎, 11-27-2012 06:48 AM
    • Replies: 2
    • Views: 4,280
    11-28-2012, 06:29 AM Go to last post
  25. [Life table] Explaining an anomalous result

    I am running a life table of marriage survival times using national data, the National Survey of Family Growth (N = ~8,500). Time-to-event is the...

    Started by ziotstats‎, 11-23-2012 01:26 AM
    • Replies: 8
    • Views: 4,083
    11-26-2012, 12:02 AM Go to last post
  26. motifs for prediction

    Hi I have identified motifs using the MEME algorithm, all of those motifs are labelled and now I'm trying to find some rules relating the motifs with...

    Started by anarichardson‎, 11-25-2012 01:14 PM
    motifs analysis
    • Replies: 0
    • Views: 1,183
    11-25-2012, 01:14 PM Go to last post
  27. Confidence interval

    Hi! I would ask you please if you can help me with this exercise, especially with paragraph b) A random sample of 960 people has a total...

    Started by Fidias‎, 11-24-2012 07:09 PM
    • Replies: 2
    • Views: 1,661
    11-24-2012, 07:18 PM Go to last post
  28. Missing data in clinical trials - HELP! Differential drop out plus ignoring questions

    Hi, I have a long format, repeated measures dataset. I have 19 variables (columns) - all representing individual questions on a 19 item scale. For...

    Started by davidallsop‎, 11-23-2012 06:13 PM
    clinical trials, mar, mcar, missing data, multiple imputation
    • Replies: 0
    • Views: 1,301
    11-23-2012, 06:13 PM Go to last post
  29. Regression with exponentially related variables

    Hi there. I would appreciate some guidance on how to approach my analysis. I have one DV and two IVs. The DV is incidence per 1000 and the two IVs...

    Started by marika‎, 11-23-2012 01:58 PM
    • Replies: 1
    • Views: 1,499
    11-23-2012, 02:50 PM Go to last post
  30. Red face multimodal histogram

    Hello, I have a histogram with multiple modes (its a length frequency to do with population recruitment in crustaceans). While I can visually...

    Started by Dasher‎, 11-19-2012 08:54 AM
    • Replies: 5
    • Views: 4,757
    11-22-2012, 06:33 PM Go to last post
  31. Likelihood ratio in Cox regression analysis?

    I have done a great deal of research without any success regarding the interpretation of likelihood ratio (LR) test in Cox regression analysis. If...

    Started by arkiaamu‎, 11-19-2012 09:42 AM
    • Replies: 1
    • Views: 10,119
    11-19-2012, 06:01 PM Go to last post
  32. Comparing HRs

    I have study population with 900 patient, of whom 200 have had an adverse outcome. This outcome can be divided into two distinct entities. I would...

    Started by arkiaamu‎, 11-16-2012 04:03 AM
    hazard ratio odss ratio
    • Replies: 2
    • Views: 1,704
    11-19-2012, 09:35 AM Go to last post
  33. Minor size differences leading to Major motifs differences?

    Hi! I've obtained some motifs from artificial DNA sequences but I'm not sure if I'm doing something wrong because when I increase the motifs size...

    Started by anarichardson‎, 11-18-2012 07:07 AM
    • Replies: 0
    • Views: 1,402
    11-18-2012, 07:07 AM Go to last post
  34. Competing events survival analysis

    Hi! Is competing risks survival analysis same as competing events survival analysis? I do not think so, but the terms are used interchangeably in...

    Started by Astha‎, 11-07-2012 10:45 PM
    competing risks
    • Replies: 1
    • Views: 1,275
    11-17-2012, 01:30 PM Go to last post
  35. Demonstrating the propensity of sheep to travel in sub-flocks - appropriate analysis?

    Hi, I hypothesize that sheep associate in sub-flocks, based on their growth rate. I.e., slow growing sheep will stay together, as will fast...

    Started by thetalldude‎, 11-07-2012 11:10 PM
    • Replies: 0
    • Views: 1,395
    11-07-2012, 11:10 PM Go to last post
  36. sampling technique

    hi am writing a proposal to conduct a study among diabetics attending out patient clinics at a tertiary hospital (diabetic centre) patinets...

    Started by mssana‎, 11-07-2012 12:55 PM
    • Replies: 1
    • Views: 1,510
    11-07-2012, 01:27 PM Go to last post
  37. Within-subject pre-post design with multiple trials pre & post

    Hi, I'm hoping someone is able to help me with my statistical analysis. My study design is a simple within-subject pre-post design, but instead...

    Started by robgat‎, 11-07-2012 01:25 PM
    multiple trials, pre-post, spss, within-subject
    • Replies: 0
    • Views: 1,425
    11-07-2012, 01:25 PM Go to last post
  38. Red face Case control, lot of parameters, N and n-Normal dist. Which test and data expression?

    Firstly, my english are not so good, sorry. I will be very happy if someone help me. I am doing a case-control study, people with and without...

    Started by Caique‎, 11-06-2012 09:19 PM
    case control, kolmogorov-smirnov, log-transform, normal distribution
    • Replies: 0
    • Views: 1,058
    11-06-2012, 09:19 PM Go to last post
  39. Descriptive statistics

    Hello I have some data and I am not sure what is the best way to present it. I have a skin disease, let's call it A. There is a treatment for...

    Started by Yankel‎, 11-05-2012 03:05 AM
    descriptive
    • Replies: 6
    • Views: 1,947
    11-06-2012, 01:32 PM Go to last post
  40. Interaction effects of nominal and ordinal variables on binary dependant variable

    Hi! I'm doing an analysis of interaction effects of one binary nominal variable (medication used), one ordinal variable (duration of therapy ;...

    Started by knedlica‎, 11-02-2012 07:00 AM
    categorical data, interaction effects, logisitic regression, logit, ordinal data
    • Replies: 2
    • Views: 3,671
    11-02-2012, 05:00 PM Go to last post
  41. Test of proportions; study design and sample size

    I want to look to see if there is an association between two conditions. Basically, patients come into dermatology and complain of an itch between...

    Started by ted‎, 11-02-2012 11:25 AM
    association, design, diagnosis, sample size
    • Replies: 0
    • Views: 1,327
    11-02-2012, 11:25 AM Go to last post
  42. Help calculating the likelihood my results were a random occurrence?

    The 5-year survival rate for leukemia is 50%, meaning about half of those diagnosed will be alive after 5 years. Suppose you have an experimental...

    Started by tto827‎, 11-01-2012 03:12 AM
    • Replies: 0
    • Views: 1,038
    11-01-2012, 03:12 AM Go to last post
  43. statistical analysis for biostats project

    hi guys, was pondering about this.... my project is about seeing how a list of about 40 different variables affect a catergorical outcome...

    Started by yznahc‎, 10-31-2012 09:44 AM
    logit
    • Replies: 2
    • Views: 1,956
    10-31-2012, 07:10 PM Go to last post
  44. Question How to become a research statistician if I have not majored in stats?

    Hello dear more experienced friends As a researcher (PHD student) stats always fascinated me and I have asked myseld the question of how I can...

    Started by sampier85‎, 10-31-2012 10:20 AM
    • Replies: 0
    • Views: 876
    10-31-2012, 10:20 AM Go to last post
  45. glm for risk ratio, endless loop

    Hi all, Thanks in advance for helping me with my problem :) Can someone please let me know how I can stop my GLM command from stalling? The...

    Started by petedigital‎, 10-28-2012 07:22 PM
    • Replies: 9
    • Views: 2,595
    10-31-2012, 02:15 AM Go to last post
  46. Rate per 100,000 persons for a quarter - divide annual population by 4?

    Hello, How do I calculate the rate per 100,000 persons of something occurring for a quarter of a year? Specifically, If I have a count of 12...

    Started by kwak123‎, 10-28-2012 11:53 PM
    rate
    • Replies: 0
    • Views: 1,205
    10-28-2012, 11:53 PM Go to last post
  47. Trouble with log-linear analysis

    Hi, I'm trying to enter data into R for analysis using generalized linear model/log-linear analysis. The data is categorical; there are 4...

    Started by gibb‎, 10-22-2012 06:50 PM
    • Replies: 1
    • Views: 1,347
    10-27-2012, 02:19 AM Go to last post
  48. Multiple Testing and Multiple Comparisons

    Hi, I'm having a bit of difficulty in deciding what measures I need to take given my situation. I have about 8 outcome variables and I use a...

    Started by jamesmartinn‎, 10-26-2012 01:47 PM
    • Replies: 1
    • Views: 1,938
    10-26-2012, 01:59 PM Go to last post
  49. Power analysis for non parametric tests (sample calculation)

    Hi, I am preparing a little presentation on power calculation for parametric tests and it occured to me that I don't know how it works for...

    Started by mousme‎, 10-24-2012 04:58 AM
    • Replies: 2
    • Views: 18,969
    10-24-2012, 10:07 AM Go to last post
  50. Comparing year - on - year illness rates - which test is statistically robust?

    Hi, What I want to do is compare year on year rates for an illness within a 4 week time frame (for the current year and the previous 2 years) for...

    Started by Reddwarf‎, 10-22-2012 04:16 PM
    • Replies: 0
    • Views: 2,060
    10-22-2012, 04:16 PM Go to last post
  51. Two sample Kolmogorov–Smirnov test

    I would like compare our ideal sample distribution to that from other samples in a study examining the age at onset (AAO) in schizophrenia, which is...

    Started by helpwithstats‎, 10-09-2012 10:00 AM
    • Replies: 2
    • Views: 27,514
    10-19-2012, 10:51 AM Go to last post
  52. power analysis for distance-based methods

    Is anyone aware of tools to perform power analyses on distance-based multivariate methods such as Permanova ANOSIM dbRDA etc...? I was...

    Started by bugman‎, 10-17-2012 02:10 AM
    • Replies: 3
    • Views: 3,171
    10-17-2012, 03:47 PM Go to last post
  53. too many censored data for suvival analysis?

    Hey, I am planning to do a survival analysis for patients with colon cancer comparing 2 groups of patients (old vs young). I am still reading...

    Started by noob‎, 10-17-2012 01:56 PM
    • Replies: 1
    • Views: 2,264
    10-17-2012, 03:22 PM Go to last post
  54. What Statistical Test to Use?

    I'm currently attempting to compare antibiotic resistance levels in two colonies of the same bacteria, but am having a hard time figuring out what...

    Started by Alloftheberries‎, 10-17-2012 01:08 PM
    • Replies: 1
    • Views: 1,533
    10-17-2012, 03:03 PM Go to last post
  55. NEJM article and lagged correlation

    In the last NEJM, there is a nice correlation between chocolate consumption and Nobel prize numbers in a given country. On the X axis there is the...

    Started by fcachat‎, 10-16-2012 08:00 AM
    • Replies: 0
    • Views: 1,297
    10-16-2012, 08:00 AM Go to last post
  56. Is Fríedman one-way or two-way ANOVA test by ranks?

    Hi, Friedman test is frequently called a one-way or two-way analysis of repeared measure ANOVA on ranks. But what is it, similar to one-way or...

    Started by Dolphin72‎, 10-13-2012 11:40 PM
    • Replies: 2
    • Views: 33,680
    10-15-2012, 12:46 AM Go to last post
  57. Patriotic Worms

    Hello all, I'm studying the Patriotic Worm… Patriotic Worms are made of RED and BLUE segments with an average of 100 segments per worm....

    Started by -P-‎, 10-10-2012 02:20 PM
    • Replies: 4
    • Views: 2,829
    10-12-2012, 02:29 PM Go to last post
  58. Superiority

    Dear forum members, I have a small question. I am planning a study and thus calculating sample size. If I check the hypothesis: H0:...

    Started by WeeG‎, 10-11-2012 04:32 AM
    • Replies: 1
    • Views: 1,778
    10-12-2012, 03:46 AM Go to last post
  59. Estimated Marginal Means

    Hi everyone, I have conducted a few Multivariate ANOVAs. As a result for my output I get the estimated marginal means. These are just the means of...

    Started by ozsunny2‎, 10-10-2012 06:22 AM
    • Replies: 1
    • Views: 3,322
    10-12-2012, 03:44 AM Go to last post
  60. Trends analysis

    Hi, Which is the most appropriate method to use when we are trying to assess trends over time for a nominal multicategory variable? For example,...

    Started by Astha‎, 10-09-2012 04:11 PM
    cmh, time, trends
    • Replies: 0
    • Views: 1,361
    10-09-2012, 04:11 PM Go to last post

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