Fifteen sources were estimated to be useful but because of how little data were collected in those searches, the bibliographies of these sources were scrutinized and 15 other sources were found.
Við heimildaleit fundust 15 nothæfar heimildir, en vegna skorts á rannsóknum var einnig leitað í heimildaskrá þeirra rannsókna sem þegar höfðu fundist og fundust þá 15 heimildir til viðbótar.