Fig. 4

Keywords analysis. The CiteScope analysis showed 8 representative keyword clusters (A), structured primarily between 1997 and 2015 and with the keywords “palliative care” and “amyotrophic lateral sclerosis”. For the VOSviewer-based knowledge mapping (B) we adopted a minimum number of occurrence keywords of 3; of 462 keywords, 96 reached the threshold; 5 clusters; links 1178; total link strength 1991. The size of nodes reflects the occurrence rate, while the connections (curves) between nodes depict their co-occurrence within a document. A shorter distance between two nodes indicates a higher degree of keyword co-occurrence. Starting from the data entered, the software generates bibliographic maps on its own where in some cases image overlaps are created