Using probabilities of enterococci exceedance and logistic regression to evaluate long term weekly beach monitoring data

Diana Aranda, Jose V. Lopez, Helena M. Solo-Gabriele, Jay M. Fleisher

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Recreational water quality surveillance involves comparing bacterial levels to set threshold values to determine beach closure. Bacterial levels can be predicted through models which are traditionally based upon multiple linear regression. The objective of this study was to evaluate exceedance probabilities, as opposed to bacterial levels, as an alternate method to express beach risk. Data were incorporated into a logistic regression for the purpose of identifying environmental parameters most closely correlated with exceedance probabilities. The analysis was based on 7,422 historical sample data points from the years 2000-2010 for 15 South Florida beach sample sites. Probability analyses showed which beaches in the dataset were most susceptible to exceedances. No yearly trends were observed nor were any relationships apparent with monthly rainfall or hurricanes. Results from logistic regression analyses found that among the environmental parameters evaluated, tide was most closely associated with exceedances, with exceedances 2.475 times more likely to occur at high tide compared to low tide. The logistic regression methodology proved useful for predicting future exceedances at a beach location in terms of probability and modeling water quality environmental parameters with dependence on a binary response. This methodology can be used by beach managers for allocating resources when sampling more than one beach.

Original languageEnglish (US)
Pages (from-to)81-89
Number of pages9
JournalJournal of Water and Health
Issue number1
StatePublished - Feb 2016


  • Historical data analysis
  • Logistic regression
  • Recreational water quality
  • Recreational water quality sampling

ASJC Scopus subject areas

  • Water Science and Technology
  • Waste Management and Disposal
  • Public Health, Environmental and Occupational Health
  • Microbiology (medical)
  • Infectious Diseases


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