Understanding discrepancies in particular years between acoustic and Daily Egg Production Method (DEPM) estimates is essential to better understand potential bias impacting both estimates, and develop a weighting per year assessing the coherence between survey estimates, to input in stock assessment models. Several plans for collaborative work have been proposed within WGACEGG to compare acoustic and DEPM indices (WGACEGG 2013, 2015, 2016), until the inclusion of such comparative approach as a formal group ToR in 2017 (ICES, 2017). Different approaches have been adopted so far, including the comparison between two egg production estimates (DEPM BIOMAN; CUFES PELGAS) and one acoustic estimate (PELGAS), analysis of the sensitivity of each estimate to its parameters, and the comparison between egg and adult maps. We here provide some rationale on how to investigate differences between acoustic and egg indices.