One of the most common problems in statistical analysis of data from water quality monitoring programs involves the so-called censored data. This study highlights how the sample mean concentration of chemical oxygen demand and phosphate variables are influenced by the estimation method, sample size and percentage of censored data. The confidence interval was used as a metric for comparison of calculated sample mean concentrations on both simple substitution and maximum likelihood estimator (MLE) methods. The results show that sample mean concentrations calculated by simple substitution method are positioned outside the confidence interval. Otherwise, the MLE method produces acceptable values for sample mean concentration, although the magnitude is constrained by sample size and percentage of censored data. The effectiveness of the method depends on an elastic limit of censoring level and sample size.
censored data; MLE method; COD; phosphate; water quality
