Lies, damned lies….

It has been said that there are three kinds of lie: lies, damned lies and statistics. The DCP Blog was reminded of this old saw on reading the following paragraph from a dismissed appeal for two houses in south Wales (DCS Number 400-020-748).

“The appellant’s evidence seeks to demonstrate that the traffic generation from 2 three-bedroom dwellings would be similar to that of one four-bedroom dwelling. This was supported by information gleaned from the TRICS® database. TRICS® is a very powerful and flexible system, and allows great variation in the calculation of both vehicular and multi-modal trip rates. It is possible, therefore, that two users of the system, applying different criteria and ranges to a task, may end up producing different results. The correct way to build a selection of surveys is to decide initial criteria and then filter the database to provide a representative sample. The incorrect method is to produce trip rates to fit a predetermined preferred figure.”

In this case the appellant was seeking to prove that the two three-bedroom dwellings proposed would generate no more traffic than one four-bedroom dwelling because permission had already been granted for one four-bedroom dwelling. The clever old council noticed, however, that different regional data or area-based data had been used to calculate the trip rate for three-bedroom dwellings and four-bedroom dwellings. The inspector decided that two dwellings would generate more traffic than the approved single dwelling.

As both the inspector and the council recognised here, statistical information can rarely be accepted at face value, even when bearing a long-established and well-respected stamp.

Section 4.1512 of DCP Online concerns the prevention of problems on the wider road network.