Total Responses in a campaign differs from the total Campaign Members

Why Total Responses in a Campaign is not the same as Total Campaign Members:

1. The Total Responses on a campaign is a calculated field of all leads + contacts that have the member status "responded" (vs Sent).

2. The Total Campaign Members include contacts and leads that have been marketed to in the past in the campaign.

3. Those two numbers should match, but sometimes those two number can be off in the following scenarios:

Scenario 1:

If the Total Responses is smaller than the total number of Campaign Members, then there are some duplicates from the Leads and Contacts which is a problem that if the multiple Campaign Member objects are inserted via the API with the same Campaign and Contact/Lead, multiple Campaign Members are created. Salesforce.com QA and Development are working on a fix for this.

Scenario 2: 

If the total number of responses is bigger than the total number of campaign members, This could occur if a lead is converted into an existing contact. It can be confirmed that this is the case, if the "Converted Leads" field is greater than the "Total Contacts" field.

Scenario 3: 

If you modified the campaign statuses after importing the campaign members, and have updated the "Responded" via the "Advanced Setup" button in campaigns, the "Responded" field in the Campaign Member records is not automatically updated. This can be fixed by forcing an update on the impacted Campaign Member records via the "Manage Members" screen, and updating the status of the Campaign Member to the same status and saving the record. This will force the "Responded" checkbox to be recalculated and checked when saved.

This means, that what determines whether a lead/contact is considered "responded" is the Responded checkbox in the Campaign Member. So in certain scenarios (like the 3rd one mentioned above) it is possible for a campaign status to be "sent" while campaign members with that status have the "responded" checkbox enabled. You can update the "responded" checkbox on the campaign members by updating them to the same status they already have  via the Campaign Members screen or you can try to update the "responded" checkbox via the Data Loader.