Linking MIMS with ActiGraph Count: An Equating Study

Abstract

ABSTRACT To convert accelerometer-based devices onto the same scale, a platform called Monitor-Independent Movement Summary (MIMS) was created and used in national studies. Yet, its physical activity (PA) intensity cutoff scores have not been established, making it less useful. This study was to link MIMS with the ActiGraph Count, known as “the Count,” using the test-equating method. A total of 81 obese participants aged 10–17 years old (male = 56%) were recruited to perform one-minute warm-ups and walking or running at different speeds with ActiGraph on hips. Data with corresponding Count and MIMS were split into training (n = 65, male = 54%) and testing samples (n = 16, male = 63%). Linear and equipercentile equating were applied to the training sample to equate MIMS onto Count, creating MIMS-equated Count (MIMS-EQ-Count), a new MIMS-based unit. High correlation (≥.84), high agreements (>.7) and kappas (mostly >.5) between MIMS-EQ-Count and the Count in both training and testing samples under both linear and equipercentile methods. Equipercentile was the best equating method because of smaller standard errors. Yielded from equipercentile equating, a table linking MIMS and MIMS-EQ-Count was constructed, from which MIMS was linked and cross-validated with the well-studied Count. MIMS can now use the rich information accumulated for the Count of ActiGraph.