MEASUREMENT OF DIET IN A LARGE NATIONAL SURVEY - COMPARISON OF COMPUTERIZED AND MANUAL CODING OF RECORDS IN HOUSEHOLD MEASURES

A diary method using household measures was employed to obtain dietary records in a large national prospective survey and a computer program , DIDO (Diet In Data Out), was designed for direct entry of the diarie s. The accuracy of this computerized coding system was examined alongs ide that of the manual coding used for a similar diary in a previous w ave, 7 years earlier, of the same survey. Accuracy was assessed by ana lysis of the errors in the coded and checked records by stringent re-c hecking of nominal 2% random subsamples of the diet diaries coded by e ach method. The mean time to code and check each of the 2086 7-day rec ords in the whole survey using DIDO was 58 minutes (SD 30) compared wi th reported results of 1-4 hours for manual methods. The mean error ra te of computerized coding and checking with DIDO was 2.3% (SD 2.1; ran ge 0-8.9) per diary in the subsample. Correcting these mistakes made i nsignificant changes to the calculated mean energy and nutrient intake s for the subsample. The percentage of individuals changing to an adja cent third of nutrient distribution after correcting unambiguous error s ranged from none (for alcohol) to 11% (for carbohydrate and calcium intake]. The mean error rate on a similar subsample of diaries from th e earlier survey which had been coded manually was significantly highe r at 5.9% (SD 4.1; range 0-17) per diary. Emphasis is laid on the impo rtance, in coding, of dealing with ambiguities in the subjects' record s, since this can affect the accuracy and the precision of the nutrien t results obtained. We conclude that the DIDO coding method has the ad vantages of greater accuracy, speed, consistency and efficient data ha ndling, and affords greater data accessibility for checking, compared with manual systems.