title: Separating fact from artifact in changes in nutrient intake over time.
abstract: OBJECTIVE
  To determine whether the differences between the procedures and nutrient databases used in the 1977-1978 Nationwide Food Consumption Survey (1977-78 NFCS) and those used in the 1987-88 NFCS could notably affect the estimated mean nutrient intakes.
  
  
  METHODS
  This was a split-sample field experiment. Seventy-two area segments were randomly selected; 10 housing units were selected in each segment and randomly assigned to one of two experimental groups.
  
  
  METHODS
  The study took place in the Philadelphia, Pa, metropolitan area.
  
  
  METHODS
  The subjects were 697 women aged 20 to 49 years.
  
  
  METHODS
  Group A was interviewed using 1987-88 NFCS 24-hour recall procedures and their nutrient intakes were calculated using the 1987-88 NFCS food codes, weight conversion factors, and nutrient database. Group B was interviewed using 1977-78 NFCS 24-hour recall procedures and nutrient intakes were calculated four ways using various combinations of 1987-88 and 1977-78 NFCS food codes, weight conversions, and nutrient database.
  
  
  METHODS
  Mean intakes of food energy and 14 nutrients were calculated.
  
  
  METHODS
  We used two-sample, multivariate t tests; univariate t tests; univariate repeated measures analysis of variance; and univariate paired t tests.
  
  
  RESULTS
  Changes in the nutrient database caused by improved analytic techniques and increased number of foods sampled were great enough to warrant revising the 1977-78 NFCS estimated intakes for iron, magnesium, and vitamins B-6 and B-12. Changes in intake of fat, vitamin A, and thiamin, however, were caused by real changes in foods so no revisions were necessary for these nutrients. Other nutrients were unaffected.
  
  
  CONCLUSIONS
  When considering changes in nutrient intake over time, it is important to correct the earlier food composition estimates so that they accurately reflect the composition of foods at the time they were consumed. This requires preserving the real differences in the composition of foods while correcting for artifactual differences attributable to improvements in the quality of nutrient data.
authors.affiliation: Human Nutrition Information Service, US Department of Agriculture, Hyattsville, MD 20782.
authors.forename: P M
authors.initials: PM
authors.lastname: Guenther
authors.forename: B P
authors.initials: BP
authors.lastname: Perloff
authors.forename: T L
authors.initials: TL
authors.lastname: Vizioli
mesh_terms: D000328:Adult; D016477:Artifacts; D003627:Data Interpretation, Statistical; D016208:Databases, Factual; D004034:Diet Surveys; D004435:Eating; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D007501:Iron / Q000008:administration & dosage; D008274:Magnesium / Q000008:administration & dosage; D008875:Middle Aged; D011736:Pyridoxine / Q000008:administration & dosage; D012107:Research Design; D012984:Software; D011795:Surveys and Questionnaires; D013831:Thiamine / Q000008:administration & dosage; D013997:Time Factors; D014801:Vitamin A / Q000008:administration & dosage; D014805:Vitamin B 12 / Q000008:administration & dosage
chemical_list: D014801:Vitamin A; D007501:Iron; D008274:Magnesium; D011736:Pyridoxine; D014805:Vitamin B 12; D013831:Thiamine