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  1. M

    Should you adjust the model for interaction for another independent variable?

    Dear all, I'm analyzing a big dataset of hospitalized patients and I use Cox regression analysis to estimate associations of different parameters with survival. I have detected that there is a significant interaction between age and sex and survival, i.e. females do worse in young patients and...
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    Is it wrong to use Chi squared test for paired data?

    Thank you, I just wanted to hear opinion like yours, but still I don't understand the real reason why both test should not be used as approaches to two different questions. What makes chi-squared illegal? It is exploratory analysis of retrospective data-set. Main stratification of renal...
  3. M

    Is it wrong to use Chi squared test for paired data?

    I would like to say that both tests should be used for different information (assess size of proportions measured by different tests - Mc Nemar, assess distribution of proportions in two groups defined by other test - Chi squared). Two different types of contingency tables from same data. Is...
  4. M

    Is it wrong to use Chi squared test for paired data?

    I'm doing a retrospective analysis of 70 patients with specific blood disease that were evaluated for frequency of renal dysfunction by 5 different ways. Data show that each of 5 approaches yield different frequency of renal disorder among those patients (45%, 37%, 17%, 8% and 6%). Since McNemar...
  5. M

    How to argument for non-significant results

    I can also argument that biologically important difference in any of the measured relative gene expression would be at least 5 delta CT units. Largest standard deviation in measurements was 2.1 for one of the gene expressions, and given these assumptions I can calculate that my study had 100%...
  6. M

    How to argument for non-significant results

    Dear all, I deal with the results of a study done on 20 patients and 20 controls who were evaluated for expression of five genes using PCR - numerical variables representing gene expression levels are provided (no apriori power analyses defining sample size were done - number of participants...
  7. M

    Is there assumption of normality behind ROC curve analysis

    Does ROC curve analysis assume that analyzed numerical variable is normally distributed?
  8. M

    log-rank test for paired samples?

    i would like to assess whether there is "spurious" improvement in survival due to different inclusion/exclusion of alternative-diagnoses-with-adverse-outcomes when one or other classification of disease is used. Most patients would be the same, but some will differ due to different criteria
  9. M

    log-rank test for paired samples?

    Is there a way to compare survival of paired samples (paired samples variant of the logrank test/Cox regression)? I would like to assess difference in survival of the "same" cohort classified by two different classifications of disease. Most of patients with the disease would be the same in...
  10. M

    How to compare patient-time data between groups

    Thank You guys for your suggestions. As I found out in the meantime I should first transform my data to be able to analyze it with Poisson regression in a way that every patient-year with specific properties makes one row of data, I have to deal with optimal way to do this though. Does anyone...
  11. M

    How to compare patient-time data between groups

    Unfortunatelty this is unknown. I only have information about general followup and events some time during this period - therefore cox regression is not an option i guess
  12. M

    How to compare patient-time data between groups

    I have a retrospective clinical dataset containing one column with general follow-up time and particular columns for each unwanted outcome containing number of unwanted outcomes during follow-up period (hospitalization, transplantation, death). Since follow-up time is not outcome specific...
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    Area under Kaplan Meier curve

    There is one thing bothering me for some time: What does area under Kaplan-Meier survival curve actally represent? Is there a plausible way to compare two areas under curve when for instance two curves cross late in follow-up and invalidate the use of log-rank test due to violation of...