Can verbal autopsies be used on a national scale? Key findings and lessons from South Africa's national cause-of-death validation study by Monique Maqungo, Nadine Nannan, Beatrice Nojilana, Erin Nichols, Diane Morof, Mireille Cheyip, Chalapati Rao, Carl Lombard, Jessica Price, Kathleen Kahn, Lorna J. Martin, Francois Bezuidenhout, Ria Laubscher, Chodziwadziwa Kabudula, Tracy Glass, Oluwatoyin Awotiwon, Nesbert Zinyakatira, Noluntu Funani, Jané Joubert, Debbie Bradshaw, Pamela Groenewald