The INDDEX24 Dietary Assessment Platform (INDDEX24) was developed to facilitate the collection of 24-h dietary recall (24HR) data. Alongside validation studies in Viet Nam and Burkina Faso in 2019-2020, we conducted activity-based costing studies to estimate the cost of conducting a 24HR among women of reproductive age using INDDEX24 compared with the pen-and-paper interview (PAPI) approach. We also modelled alternative scenarios in which: (1) 25-75 % of dietary reference data were borrowed from the INDDEX24 Global Food Matters Database (FMDB); (2) all study personnel were locally based and (3) national-scale surveys. In the primary analysis, in Viet Nam, the 24HR cost US $111 004 ($755/respondent, n 147) using INDDEX24 and $120 483 ($820/respondent, n 147) using PAPI. In Burkina Faso, the 24HR cost $78 105 ($539/respondent, n 145) using INDDEX24 and $79 465 ($544/respondent, n 146) using PAPI. In modelled scenarios, borrowing dietary reference data from the FMDB decreased the cost of INDDEX24 by 17-34 % (Viet Nam) and 5-15 % (Burkina Faso). With all locally based personnel, INDDEX24 cost more than PAPI ($498 v. $448 per respondent in Viet Nam and $456 v. $410 in Burkina Faso). However, at national scales (n 4376, Viet Nam; n 6500, Burkina Faso) using all locally based personnel, INDDEX24 was more cost-efficient ($109 v. $137 per respondent in Viet Nam and $123 v. $148 in Burkina Faso). In two countries and under most circumstances, INDDEX24 was less expensive than PAPI. Higher INDDEX24 survey preparation costs (including purchasing equipment) were more than offset by higher PAPI data entry, cleaning and processing costs. INDDEX24 may facilitate cost-efficient dietary data collection.

Technology-enabled approaches to conducting 24-h dietary recalls (24HR) may reduce dietary assessment bottlenecks in low-resource settings. However, few studies have assessed their performance relative to conventional pen-and-paper interview (PAPI) approaches and none have validated performance against a benchmark (e.g. weighed food record (WFR)) in a low- and middle-income country (LMIC). This study assessed relative accuracy and cost-effectiveness of INDDEX24, a technology-enabled approach to conducting 24HR, compared with a PAPI approach and against an observer WFR. Women aged 18-49 years from northern Viet Nam (n 234) were randomly assigned to be interviewed using INDDEX24 or PAPI 24HR following a WFR. The two one-sided t test approach assessed the equivalence of each recall modality to the benchmark. Difference-in-differences analysis compared the recall-benchmark results across modalities. Cost per percentage point of accuracy for INDDEX24 and PAPI was derived from accuracy results and the cost to conduct the 24HR. The PAPI and INDDEX24 24HR were statistically equivalent to the WFR for all nutrients except vitamin A. INDDEX24 diverged significantly less than PAPI from the WFR for Fe (0·9 v. -1·3 mg) and PAPI diverged less for protein (-3·7 v. 7·9 g). At the individual level, 26 % of PAPI and 32 % of INDDEX24 respondents had energy intakes within +/- 10 % of the WFR. INDDEX24 cost $111 004 and the PAPI cost $120 483 (USD 2019), making INDDEX24 more cost-effective across most indicators. INDDEX24 was an accurate and cost-effective method for assessing dietary intake in the study context and represents a preferred alternative to PAPI 24HR in Viet Nam and other LMIC.