F-105 and A-4 loss rates over North Vietnam

As everybody here probably knows, USAF F-105 Thunderchiefs and USN A-4 Skyhawks bore the brunt of the Rolling Thunder campaign from 1965 to 1968 and suffered accordingly. The F-105 and A-4 losses over North Vietnam were 282 and 173 respectively.

Now the harder part. What were their loss rates (losses/sorties) and how they compare? What factors contributed to the difference?

Cheers,
Sunho