Laser Height Measuring Device Study in Vietnam

This is a prospective, cross-sectional validation study conducted in Quang Nam Province, Vietnam, to evaluate a portable laser-based anthropometric device for measuring recumbent length in children aged 0-23.9 months and standing height in children aged 24-59.9 months. The study is embedded within the sampling frame of the national routine child-growth monitoring activities. Quang Nam was selected because it includes hot and humid field conditions, where a portable device intended for community outreach must perform reliably.

The investigational device is a compact, battery-powered laser device designed for field measurement of child length and height. It will be evaluated against the ShorrBoard, a wooden length/height board used as the reference measurement method. The laser device is designed to be lighter, more portable, and easier to transport than conventional boards while retaining the measurement performance needed for child growth assessment in outreach settings. Measurements will be performed by trained community health workers and expert anthropometrists to assess device performance under conditions relevant to routine service delivery.

All households with children younger than 60 months in selected villages will be invited to participate. Data collection will occur across eight villages. Teams will include two measurers and one recorder; expert teams will remain consistent across villages, while volunteer community-health-worker teams will be recruited and trained for groups of villages.

Each enrolled child will undergo repeated length or height measurements with both the laser device and ShorrBoard. Children younger than 24 months will be measured lying down for recumbent length; children aged 24-59.9 months will be measured standing. Each device will be calibrated using a meter rule before use. Measurements will be recorded to the nearest 0.1 cm. When two repeated measurements differ by more than 0.7 cm, a third measurement will be obtained; the two closest values will be retained for analysis.

To reduce potential measurement-order bias, the device used first by community health worker teams will alternate by day. Individual staff roles will remain stable during each data-collection day. Measurement locations will be designated by device, and teams will rotate between locations to balance environmental conditions such as lighting and temperature. Measurements by the different teams will be separated by at least 30 minutes to reduce recall effects while allowing assessment of consistency across time.

The sample size will be calculated to provide 90% statistical power to establish equivalence between the laser device and the conventional ShorrBoard using the Two One-sided Tests (TOST) procedure, with a prespecified equivalence margin of ±0.2 cm and a 5% significance level (α = 0.05). Assuming a true mean difference of 0 cm and a standard deviation of paired measurement differences of 0.671 cm, approximately 124 children with complete paired measurements will be required per age group. After adjusting for an anticipated 20% dropout or incomplete measurement rate, the minimum recruitment target will be 155 children per age group, or 310 children in total. Because the study will be conducted alongside routine growth-monitoring activities, all eligible children who present within the selected catchment areas may be measured, even if the target sample is exceeded.

Agreement between the laser device and reference measurements will be assessed using Bland-Altman methods, including the mean between-method difference and limits of agreement. Inter-method technical error of measurement will also be calculated. Reliability and repeatability will be assessed with intraclass correlation coefficients, including consistency across measurers, devices, and measurement time points. Precision of repeated measurements will be assessed using standard deviations, coefficients of variation, and intra-rater technical error of measurement. Analyses will additionally examine whether the choice of measurement device changes categorical classification based on weight-for-length/height and length/height-for-age indices; paired categorical classifications will be compared using McNemar's test.

Data will be collected electronically using KoboCollect on Android devices, with paper tools available as backup. Electronic forms will incorporate required fields, range checks, and skip logic to reduce entry errors. Equipment calibration results will be recorded before measurement sessions. Field data will be reviewed daily using Excel and ENA for SMART/ENA 2008 software to identify digit preference, implausible anthropometric values, or enumerator-specific quality concerns. Measurements requiring verification may be repeated the following day, and field staff may be retrained when data-quality checks indicate a need.

Data will be transferred from encrypted, password-protected devices to the World Vision KoboCollect server when connectivity is available and subsequently to secure London School of Hygiene \& Tropical Medicine servers for processing. Identifiable information will be stored separately from study measurements and linked only through a study identifier. The analytical dataset will be de-identified before analysis. Data cleaning, processing, and analysis will be conducted in R using reproducible analysis scripts. Missing, unavailable, or implausible measurements will be reviewed against source records and protocol-based quality rules; measurements that cannot be verified will be documented and handled as missing in the relevant analysis.

This is a minimal-risk, non-invasive measurement study. Trained staff will follow standardized procedures intended to maintain children's comfort and safe positioning during measurement. Children identified through study measurements as meeting criteria for severe wasting will be referred to the nearest health facility for assessment and services according to applicable national guidance.