We Don't Live In Perfect
My recent abstinence-related post has elicited this comment: [When it comes to abstinence] [t]here is no difference between perfect use and typical use. If you have sex, you are no longer abstinent. That is incorrect.
If you are using the abstinence* birth control method and you engage in sexual activity, it doesn't mean you are no longer using the method. It means you are using the method either incorrectly, or inconsistently; the very definition of typical use.
[*We are discussing continuous, as opposed to periodic, abstinence.]
Recall the definitions (emphasis mine):
Researchers have two different ways of measuring the effectiveness of contraceptive methods. "Perfect use" measures the effectiveness when a contraceptive is used exactly according to clinical guidelines. In contrast, "typical use" measures how effective a method is for the average person who does not always use the method correctly or consistently.
Let's clear up the confusion by using a case study.
Assume there are three women--one uses an intrauterine device (IUD), one uses a diaphragm, and one uses abstinence. Now, in a perfect use scenario all three methods are used correctly, and consistently.
For the IUD, correct use means a versed physician inserts the IUD properly, and its continued correct positioning is checked periodically (the woman feels for the string, the MD checks it, usually during the annual exam).
For the diaphragm, correct use means, at first visit, the MD fits the proper size, and, subsequently, the woman checks its integrity; inserts it in the proper position (covering the cervical os); uses spermicide properly (e.g., during first use, and before each subsequent ejaculation); and leaves the diaphragm in place for the indicated amount of time.
For abstinence, correct use means the woman refrains from sexual activity.
For all three methods, consistent use means the method is used each and every time sexual activity is to take place.
Of course, like the commercial says, "We don't live in Perfect". In real life (aka typical use scenario) each of our three women has two hurdles to overcome: using the method correctly, and using it consistently.
The woman using the IUD has the easiest job: assuming proper initial placement, once the IUD is inserted she doesn't have to do anything for the IUD to work. Hence, she's almost guaranteed correct use. I said "almost", because, although rare, it's possible for the IUD to become displaced [it can be expelled without the woman even knowing it; it can perforate the uterus--for the Cu T brand, the incidence is 0.6/1000 insertions].
Also, consistent use is guaranteed by the IUD's intrauterine location. In other words, since your uterus is present for every sexual encounter, so is your birth control method.
For this method, perfect use and typical use are almost the same. [One of the many reasons why, in my professional opinion, the IUD is an excellent method of birth control.]
An aside: The failure rates for perfect/typical use depend on the type of IUD used. To give you an idea, for the copper Cu T brand, the perfect use failure rate is 0.6%, and the typical use one is 0.8%. Keep these rates in mind as we'll come back to them shortly.
The woman using the diaphragm can run into problems with both correct, and consistent use. Recall all the method requirements for correct use--check for defects, proper fit and placement, time spermicide and method placement/withdrawal. In real life, it's fairly easy to miss any one of these steps, or to make a mistake. These are correct use problems.
Moreover, the woman might not use the diaphragm each and every time she has intercourse [for whatever reason--she forgets, diaphragm not handy, she's not comfortable inserting it, partner objects, etc.].
Finally, all the woman practicing abstinence has to do, to use the method correctly, is to not engage in any sexual activity. Correct use problems can crop up because there might be confusion about, or different interpretations of, what constitutes "sexual activity", etc.
Also, she might run into problems when it comes to consistent use. Like the woman using the diaphragm, she might not abstain each and every time [for whatever reason].
Another aside: So, for the Cu T IUD brand the failure rate is 0.6% with perfect use, and 0.8% with typical use. Compare this with the [combination] Pill's failure rates: 0.1% with perfect use, and 5% with typical use.
The Pill has a lower perfect use failure rate than the IUD. However, the IUD has a lower typical use failure rate. Why? Because in real life it's much easier to use the IUD correctly and consistently. You can't forget "to take" the IUD, nor can you "run out" of it. [Incidentally, for the diaphragm (with spermicide) the failure rates are 6% with perfect use, and 20% with typical use. For continuous abstinence, the perfect use rate is 0%; the typical use failure rate is unknown.]
This is a good illustration of the "just because a method has a low perfect use failure rate doesn't mean its typical use rate is equally low" concept. You cannot guess the typical use failure rate from the perfect use rate. And, without knowing the typical use effectiveness, you cannot make an informed decision about which method of birth control is best suited to your particular circumstances.
Just because you know how to use a method correctly--you know how to insert the diaphragm properly, you know abstinence entails not engaging in sexual activity--does not mean you will actually use the method correctly. Neither does knowing you should always use your birth control method, if you do not wish to become pregnant, translate into consistent use. [Any physician who's ever discussed birth control with a teenaged patient has had this conversation: MD "Are you sexually active?"; T "Yes"; MD "Are you planning a pregnancy?"; T "No"; MD "So, what method of birth control are you currently using?"; T (smiles demurely) "Umm...nothing."; MD "Do you know how pregnancy happens?"; T (slightly offended) "Yes, of course I do!"; MD "Well, ...?"; T (smiles meekly, blushes, and develops a sudden, and intense interest in the details of the examining room floor)]
Bottom line: Like with any other method of birth control, when you use abstinence there is a difference between perfect use and typical use. Since we don't know what this method's typical use failure rate is, any pronouncements about its effectiveness are so much rhetoric. And, when it comes to making decisions about your health [among other things], vacuous statements are a poor substitute for actual information.
Failure rates: Williams 21ed, p 1520