Visual sewer inspection: detail of coding system versus data quality?

In order to provide information about the decisions on proactive and reactive maintenance, sewers are visually inspected. Previous research showed that the quality of visual inspection data is questionable. A coding system prescribes which and how defects should be recorded. This article studies the influence of the coding system on quality of inspection data. A database with the examinations of the Dutch sewer inspector course is studied. Through time, 10 photos of the inside of a sewer were evaluated according to two different coding systems: the concise NEN3399:1992 and the more detailed and extensive NEN3399:2004.This article compares both coding systems by evaluating candidate responses to photos showing sewers with clearly visible defects. Results show that added detail in the coding system of 2004 leads to more mistakes. Therefore, it can be concluded that the increase in detail does not lead to more information.