A large exposure study requires careful consideration regarding the variables to be studied, the number of replicates needed to produce sound statistics, the length of exposure time, and--in the case of correlating accelerated and real-time weathering--how best to make the comparison in a meaningful way. A ten-year cooperative study between the National Coil Coating Association and ASTM International was undertaken--and completed--many years ago. Although this study involved liquid coil coatings, the process used to evaluate the data (>10,000 data points) and the use of Spearman Rank Correlation to evaluate the level of correlation between real-time and accelerated weathering is useful to understand for anyone who wishes to engage in a similar study, regardless of the coatings being considered. This presentation will provide an overview of the experiment and provide a detailed discussion of why and how Spearman Rank Correlation was used for this weathering study. A review of the ten-year correlation data will also be discussed.
David Cocuzzi, Technical Director, National Coil Coating Association