I'm convinced that they're wrong.
'Convinto' — con-VIN-to. Stress on the second syllable. 'Abbiano' — AB-bia-no — congiuntivo of 'avere'.
Use to express a strong, firm opinion — you're not just guessing, you're convinced. More emphatic than 'penso che' — used when you feel certain.
'Essere convinto' means to be convinced or certain. Despite this certainty, Italian grammar still requires the subjunctive 'abbiano' after 'sono convinto che'. This is a key feature of Italian: subjunctive follows verbs of opinion even when the opinion is strong.
Sono sicuro/a che sia così.
I'm sure that's how it is.
'Sono sicuro/a che' + subjunctive — same pattern. Gender: sicuro (m) / sicura (f)
Ne sono certo/a.
I'm certain of it.
'Ne sono certo/a' — uses 'ne' (of it) as pronoun. Very definitive statement.
Non ho dubbi al riguardo.
I have no doubts about it.
Most emphatic — zero doubt stated explicitly. Used for very strong positions.
In Italian debate culture, backing up an opinion with data or evidence ('i numeri', 'i dati') significantly strengthens your position. Italians respect well-argued positions even when they disagree with the conclusion.