You can change the way Marketo ties contacts to opportunities for first- and multi-touch attribution, lead conversion metrics, and the marketing-influenced opportunity flag.
Under the Admin section, click Revenue Cycle Analytics.
Click the Edit link under Attribution.
Select an option and click Save.
When using Implicit, Marketo will always examine all contacts associated to the account regardless of role. Marketo strongly recommends using Explicit mode. Using Implicit may create false positives; i.e., people with credit for an opportunity despite having no real influence in the opportunity. Use Implicit with caution.