Reproducibility and validity of the Diet Quality Index Revised as assessed by use of a food-frequency questionnaire.
BACKGROUND
The Diet Quality Index Revised (DQI-R) is a dietary assessment instrument based on 10 dietary recommendations reflecting dietary guidelines and policy in the United States.


OBJECTIVE
The objective of this study was to assess the reproducibility and validity of the DQI-R as measured by use of food-frequency questionnaires (FFQs).


METHODS
Diet was assessed separately by two FFQs at a 1-y interval and by two 1-wk diet records. DQI-R scores were computed from each method. Venous blood specimens were collected for measurement of dietary biomarkers. Participants (n = 127) were men aged 40-75 y in a validation study of the Health Professionals Follow-up Study.


RESULTS
Mean DQI-R scores were 69.5 for FFQ-1, 67.2 for FFQ-2, and 62.0 for the diet records out of a possible score of 100. The reproducibility correlation for the 2 FFQ scores was 0.72. Correlations between scores for each of the 2 FFQs and diet records were 0.66 (FFQ-1) and 0.72 (FFQ-2). DQI-R scores from FFQ-2 were directly correlated with plasma biochemical measurements of alpha-carotene (r = 0.43, P < 0.0005), beta-carotene (r = 0.35, P < 0.005), lutein (r = 0.31, P <0.005), and alpha-tocopherol (r = 0.25, P < 0.05) and were inversely correlated with plasma total cholesterol (r = -0.22, P < 0.05).


CONCLUSIONS
These data indicate reasonable reproducibility and validity of the DQI-R as assessed by an FFQ. Future studies are needed to examine whether this index and other instruments of diet quality can reliably predict disease outcomes.
Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA. pknewby@post.harvard.edu
P K
PK
Newby
Frank B
FB
Hu
Eric B
EB
Rimm
Stephanie A
SA
Smith-Warner
Diane
D
Feskanich
Laura
L
Sampson
Walter C
WC
Willett
D000328:Adult; D000368:Aged; D002338:Carotenoids / Q000097:blood; D002784:Cholesterol / Q000097:blood; D015930:Diet Records; D006801:Humans; D014975:Lutein / Q000097:blood; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D018673:Nutrition Policy; D009747:Nutritional Physiological Phenomena; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D024502:alpha-Tocopherol / Q000097:blood; D019207:beta Carotene / Q000097:blood
D019207:beta Carotene; D002338:Carotenoids; C041635:alpha-carotene; D002784:Cholesterol; D024502:alpha-Tocopherol; D014975:Lutein