Recent content by Johann Kotze

  1. J

    ANOVA RCB design; multiple items in groups

    Good day! I have a study that seems to fit the criteria for an ANOVA using a randomized complete block design. The research is on the effect of one drug on a blood parameter, but we assume that another measurable factor also affects the blood parameter (hence our blocking). Yet, we cannot...
  2. J

    Poisson model on moving averages: non-discrete

    I have a model that is based on counts of cases. It follows a poisson distribution quite well but we are unhappy about the results of the model. In order to improve it we wanted to use moving averages of the counts instead of the counts themselves as the dependent variable, but this changes my...
  3. J

    Reporting the formula for a mixed model in a paper

    I want to report the basic formula of my mixed model. Everywhere I look for a template the equations seem way too complicated for a journal whose focus is not the stats itself. Before, I had a fixed effects logistic regression model, so I had a paragraph in my paper going something like...
  4. J

    Normal logistic regression vs a mixed model; which to use? benefits gained?

    I have some evidence to suggest that one vaccine was far superior over another and resulted in the local elimination of a disease. Because it affects pharmaceutical companies the information is sensitive so I will share as much as I can. I analysed the following data set using logistic...
  5. J

    Confidence intervals: normal vs t-distribution (central limit theorem)

    Hi all! We did a serological survey for a disease taking 300 samples in a population of 50 000. If our sample mean gives a 2% prevalence. How do we work out the confidence intervals? I have all the formula's and there are great CI calculators on the web BUT seeing that is only one survey...
  6. J

    Logit regression interaction/moderation: what to do about it?

    Hi all! I have a multivariable logit regression model that has two terms showing two-way interaction (the interaction also makes biological sense.) So what am I to do about it? Do I just mention it in my findings? Do I remove one of the variables? (How do I decide which one?) I...
  7. J

    Is Chi-sqaure the right test for analysing these disease test results?

    Hi All! I have three tests testing for three different strains of the same disease. Unfortunately the tests are not very specific since antibodies (and therefore positive results) to the three strains are common in most populations. If however, there is a true outbreak of the disease, then of...