Is the use of a condom or the withdrawal method with the pill more effective than the pill by itself?

Yes. The pill is about 97% effective with typical use, 99% effective with perfect use (hint: read the directions and follow them). That leaves a 3% chance with typical use and a 1% chance with perfect use of getting pregnant.

With typical use, condoms are about 82-90% effective (10-18% of couples using this as sole birth control method will get pregnant over the course of a year), but 98% effective with perfect use. Just so we don't overestimate things, these calculations use the worst typical effectiveness.

If I am a typical pill user I have a 3% chance of getting pregnant. If I combine that with a condom, then I have a ((3)x(0.18))% chance of getting pregnant, or only 0.54% now.

If I am a typical pill user and combine that with the pull-out method (effectiveness about 70% on a good day), then my chances of getting pregnant are ((3)x(0.3))%, or 0.9%.

As you can see, the withdrawal method by itself isn't particularly effective, but because the pill is very effective at preventing pregnancy, the chances of it happening are small.

The pill+condom combination is more effective, because condoms have a better success rate than the withdrawal method.

In addition condoms help prevent STDs