Visual inspections for property asset condition assessments

Recently I’ve been looking at condition surveys again. As part of this my attention was drawn to some research on visual inspection of bridges in the States. As serious research in this area is generally hard to find I looked at it to see if there were any lessons to be learnt. I was impressed by the quality and thoroughness of the work. What they did was to get 49 practicing bridge inspectors from 25 states to carry out inspections using the national rating system on 10 bridges. Below I have taken the results for one of the bridges that appeared to me as being typical.

As you can see there are 10 ratings in the USA for bridges and only about 40% of the inspectors agree about the rating of each of the three elements for this particular bridge. Now before you start to say that would never happen here, remember all these guys had on average just over 10 years experience inspecting critical assets similar to this one. This evidence seems to point to the fact that these are typical results for visual inspection of built assets.
Some years ago I was told that we human beings were generally good at distinguishing between up to about seven single faceted entities. More than this our ability to differentiate between one and the next one deteriorates rapidly. With this in mind I tried amalgamating the ratings into five and the results were as follows:

Now with only five ratings, which is more like the number I’m used to, between 61% and 74% of the inspectors agree about the rating of each of the three elements. Although a significantly less variable result it is still one worthwhile remembering when reviewing visual inspection data.