Statistical analysis of data from dilution assays with censored correlated counts

Jorge Quiroz, Jeffrey Wilson, Satrajit Roychoudhury

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Frequently, count data obtained from dilution assays are subject to an upper detection limit, and as such, data obtained from these assays are usually censored. Also, counts from the same subject at different dilution levels are correlated. Ignoring the censoring and the correlation may provide unreliable and misleading results. Therefore, any meaningful data modeling requires that the censoring and the correlation be simultaneously addressed. Such comprehensive approaches of modeling censoring and correlation are not widely used in the analysis of dilution assays data. Traditionally, these data are analyzed using a general linear model on a logarithmic-transformed average count per subject. However, this traditional approach ignores the between-subject variability and risks, providing inconsistent results and unreliable conclusions. In this paper, we propose the use of a censored negative binomial model with normal random effects to analyze such data. This model addresses, in addition to the censoring and the correlation, any overdispersion that may be present in count data. The model is shown to be widely accessible through the use of several modern statistical software.

Original languageEnglish (US)
Pages (from-to)63-73
Number of pages11
JournalPharmaceutical Statistics
Issue number1
StatePublished - Jan 1 2012


  • R programming language
  • censored correlated count data
  • censored mixed negative binomial regression
  • hierarchical likelihood

ASJC Scopus subject areas

  • Statistics and Probability
  • Pharmacology
  • Pharmacology (medical)


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