5 6 7 1. Summary 8 Since 2004, podcasts have emerged as a decentralised medium for science communication to the global public.9However, to-date, there have been no large-scale quantitative studies of the production and dissemination of 10 science podcasts. This study identified 952 English language science podcasts available between January and 11 February 2018 and analysed online textual and visual data related to the podcasts and classified and noted key 12 production parameters. It was found that the total number of science podcast series available grew linearly 13 between 2004 and 2010, and then exponentially between 2010 and 2018. 65% of science podcast series were hosted 14 by scientists and 77% were targeted to public audiences. Although a wide range of primarily single-subject science 15 podcasts series were noted, 34% of science podcast series were not dedicated to a science subject. Compared to 16 biology and physics, chemistry may be under-represented by science podcasts. Only 24% of science podcast series 17 had any overt financial income. 62% of science podcast series were affiliated to an organisation; producing a greater 18 number of episodes (median = 24, average = 96) than independent science podcast series (median = 16, average = 19 48). This study provides the first 'snapshot' of how science podcasts are being used to communicate science to 20 public audiences around the globe. 21 22receive listener feedback and facilitate discussion. Such "two-way dialogue" -not typically available in traditional 58 broadcast and print media -can help improve public trust in science". [15,16] It has been speculated that podcast 59 audiences may feel more personally connected to the producers of podcasts than of other forms of media. [17] 60 Additionally, podcasts have been demonstrated to improve scientific information uptake in students, medical 61 patients, and the public. [18][19][20] These advantages combine to make podcasts an attractive medium for science 62 communication for both independent science communicators and larger organisations. Examples of large 63 organisations with science podcasts include: professional scientific societies, space agencies, funding 64 agencies/charities, scientific journals, government agencies, schools, and universities.
65Audience engagement metrics for podcasting are either not well developed or not publicly available. [21] 66 Therefore, studies of podcast listener demographics have primarily relied on audience surveys. In 2018, a 67 commercial survey of general podcast audiences in the USA found that both men and women listen to podcasts in 68 similar proportions (27% and 24% of respondents respectively); that podcast audiences skew towards young 69 adults; that podcast audiences are well-educated, and that individuals typically listen to an average of 7 podcasts 70 per week (corresponding to an average of 6 hours 37 minutes). [22] In contrast, a study of science podcast audiences 71 in Brazil by Dantas-Queiroz et al.[10] found that an overwhelming proportion (87%)...