Since the building permit data are extracted from municipal administrative documents, two types of response errors are possible: errors attributable to the permit applicant and errors in transcription by the responding municipality. However, experience has shown that transcription errors are not very common and the increasing number of municipalities producing computerized reports tends to reduce the frequency of this type of error. Errors attributable to an understatement of the cost of construction are more probable. Since permit fees are in most cases based on the value of the construction, this leads unquestionably to under-estimation of project values.