The ambient air quality standard for ozone in Taiwan is 0.12 ppm (hourly average). To protect human health, this standard is not to be exceeded by the observed hourly ozone concentration. To test compliance, each day’s maximum hourly ozone concentration is identified and the eighth highest value of the 365 daily hourly maxima for the entire year is calculated. To account for the uncertainty in measurement, the regulation stipulates using the three-year moving average of the eighth highest value to compare with the standard. In this study, observed ambient hourly ozone data from 1998-2002 at 9 continuous monitoring stations maintained by the government were collated and the eighth-highest concentration (MAX8) was calculated for each site by year. For the estimate of confidence interval for MAX8, a linear regression of ozone concentrations on their ranks was applied, as well as a quadratic logistic regression of odd ratios on ozone concentration. To estimate the confidence interval using the quadratic equation for inverse prediction, a Monte Carlo simulation was carried out in conjunction with the latter method. By taking into account the uncertainty expressed by the confidence interval, it was shown that MAX8 did not exhibit differences statistically for all stations in the period.