Actually copied from Wikipedia, hence the left in citation markers, but Wikipedia's citations are:
1: Mícheál Ó Siochrú/RTÉ ONE, Cromwell in Ireland Part 2. Broadcast 16 September 2008.
2: O'Callaghan, Sean (2000). To Hell or Barbados. Brandon. p. 85. ISBN 978-0-86322-272-6.
3: Higman, B. W. (1997). Knight, Franklin W. (ed.). General History of the Caribbean: The slave societies of the Caribbean. 3 (illustrated ed.). UNESCO. pp. 107, 108]. ISBN 978-0-333-65605-1.
The 15-80% figure sources are:
15–25% Padraig Lenihan, Confederate Catholics at War, p112
50%: The History and Social Influence of the Potato, Redcliffe N. Salaman, Edited by JG Hawkes, 9780521316231, Cambridge University Press
How many died during Cromwell’s campaign?
83%: The Cromwellian Settlement of Ireland by John Patrick Prendergast
I would suspect perhaps that the 83% figure is probably going so far as to blame Cromwell for The Great Famine of 1845, and definitely his "to hell or to Connacht" campaign of dispossessing native Irish landowners was a contributing factor in the economic structure that led to it, but I think 200 years apart is enough to not directly attribute that as "deaths to Cromwell's invasion".
1: Mícheál Ó Siochrú/RTÉ ONE, Cromwell in Ireland Part 2. Broadcast 16 September 2008.
2: O'Callaghan, Sean (2000). To Hell or Barbados. Brandon. p. 85. ISBN 978-0-86322-272-6.
3: Higman, B. W. (1997). Knight, Franklin W. (ed.). General History of the Caribbean: The slave societies of the Caribbean. 3 (illustrated ed.). UNESCO. pp. 107, 108]. ISBN 978-0-333-65605-1.
The 15-80% figure sources are:
15–25% Padraig Lenihan, Confederate Catholics at War, p112
50%: The History and Social Influence of the Potato, Redcliffe N. Salaman, Edited by JG Hawkes, 9780521316231, Cambridge University Press How many died during Cromwell’s campaign?
83%: The Cromwellian Settlement of Ireland by John Patrick Prendergast
I would suspect perhaps that the 83% figure is probably going so far as to blame Cromwell for The Great Famine of 1845, and definitely his "to hell or to Connacht" campaign of dispossessing native Irish landowners was a contributing factor in the economic structure that led to it, but I think 200 years apart is enough to not directly attribute that as "deaths to Cromwell's invasion".