And, what does it mean if they are 99% effective?
When looking at the effectiveness of birth control (pills or not), the number you find by the manufacturer is how effective it is when used perfectly (i.e. you take the pills everyday, or for condoms, that you wear the condom correctly and it is not expired or broken). The effectiveness does not depend on brand name but rather the type of birth control pill. For example, progesterone only birth control pills have different effectiveness than progesterone and estrogen birth control pills. The effectiveness numbers for birth control are determined from careful scientific research of trials of women and are very accurate.
The key thing to note is that birth control methods can only be as effective as promised if one is using them correctly. This is something to consider when choosing between birth control pills, intrauterine devices, condoms, or more, since some of these are easier to use perfectly than other. You can learn more on our contraception page.