Facts, Figures and Fictions in Genetic Counseling

Genetic counselors have a love/hate relationship with numbers. We sometimes sniff with contempt at numbers , and nobly proclaim that psychosocial issues are the real business of genetic counseling. On the other hand, patients and referring physicians demand concrete answers, so we spend an inordinate amount of time  discussing statistics and risk figures. And, truth be told, hard data is less complicated to address than complex psychological issues. With numbers, as Casey Stengel used to say, “You can look it up” – but counseling requires us to use our skills to fly by the seat of our pants.

This focus on numbers has led to the particularly absurd practice of evaluating the effectiveness of genetic counseling  by measuring accuracy of patient recall.  Not surprisingly, patients often demonstrate poor recall of any but the simplest facts. Surely by now we have learned that patients are not calculating machines! Whatever information we provide passes through patients’ complicated emotional, neurobiological, and cultural filters and out the other end comes a jumbled understanding of technical information that plays out in a complex psychosocial milieu.  Yet despite their fairly consistent inability to remember much of what we tell them, patients usually make good decisions. Many researchers are at last questioning the validity of  using recall to measure effectiveness – it’s a counseling session, not a final exam, for chrissakes’ almighty.

I am relieved that researchers are developing alternative ways of evaluating genetic counseling. What intrigues me  about numbers, though, is a question that almost no researcher has asked – “Why do genetic counselors (or any health professional) choose to use a certain set of numbers when counseling patients?” It’s a given that all research studies are flawed, and therefore the numbers generated by studies are flawed, some tragically so. I would like to believe that we carefully evaluate and compare studies, and choose those with the soundest methodologies and largest sample sizes to generate risk figures for use in genetic counseling. But I am not convinced this is always the case. Let me illustrate with 3 common examples from genetic counseling practice.

1) The single most widely cited genetic counseling statistic – for at least  30 years – is the mythical 0.5% miscarriage rate of amniocentesis. This number is well enshrined in text books, journal articles, and our collective memory. It’s usually presented to patients, with some variation, as “Amnocentesis has a half-percent miscarriage rate.” This may then be followed by a statement like  “But at our center, the miscarriage rate is X” (inevitably some number lower than 0.5%), or  perhaps “More recent studies have shown a lower rate.” These “statements of fact”  are so incorrect that they border on falsehoods. First off, as I have pointed out (ad nauseum, to some) no study has ever shown a 0.5% miscarriage, period, end of story. Second, no individual center or physician knows their own miscarriage rate. The only way to determine a center’s or individual physician’s pregnancy loss rate is through a randomized controlled study within a center. This requires sample sizes – and raises ethical issues – well beyond the means of even the largest and best financed clinics. In the absence of such a study, providing a center- or physician-specific risk is biased guesswork at best, and fraudulent deception at worst. Third, while some recent studies have shown low rates of fetal loss, the very first multi-institutional US study of amniocentesis published in 1976 found no statistically significant difference in the loss rate between the amnio/no amnio groups.  The most honest and accurate thing you could say to patients is”Studies have shown that amniocentesis has a loss rate anywhere from no increased risk on up to about 1%. There is no reason to believe that this center’s loss rate is different than published data, although we lack the statistical evidence from our own center to prove that assertion”. How can you justify saying anything other than that?

2) Maternal serum screening for aneuploidy is a mainstay of patient referrals to genetic counselors. Parents are put through the emotional ringer, and make life-changing decisions based on the results of these tests. The aneuploidy risk is usually stated as a precise-sounding fraction, e.g. 1/127.  To soften the blow, we may re-state it as a “barely 1%”, or re-frame it as more than a 99% chance that the fetus does not have an aneuploidy. But no matter how you say it, the statistic itself still carries an air of truth and authority, etched in stone and handed down to us  from the Lab Gods. Yet  a single blood sample from one patient analyzed in different labs can result in very, very different aneuploidy risks from each lab. So which number is right? Which lab do we swear by and why?

3) In cancer counseling, it is common practice to assess the likelihood of carrying a BRCA or other gene mutation by using one of the many risk assessment models – BRCAPro, FHAT, PAT, BOADICEA, etc. While each model has its strengths and weaknesses, it is pretty clear that the same family, when assessed by multiple models, can wind up with very different BRCA carrier probabilities. And although the adherents, er, uh, I mean, supporters of a particular model will tout its strengths, when it comes down to it, all models perform about the same, and the models usually perform extra poorly at the upper and lower risk thresholds. Why use one number over the other? In fact, why use any number at all (other than for research purposes)?

I suspect that which numbers we use tells us more about ourselves than about any absolute or approximate reality. I think it also makes us  very uncomfortable when the pillars of truth are found to be structurally unsound; we are not comfortable “going there.” Do we use a particular set of numbers because that’s what our bosses told us to do? Because that’s what we learned in school? Because we just read an article by some respected and clever researcher, so we assume the numbers he or she uses must be pretty good? Are there deeper and subtler reasons? For example, I have argued that 0ur imperfect collective memory of the risks of amniocentesis has allowed us to construct a more palatable reason for offering amniocentesis at age 35,  a justification based on a semi-fictional medical risk/benefit assessment rather than based on the more realistic reason of economic gains of preventing births of babies with Down syndrome.

Why do you think you use the numbers you do? Share your thoughts on this, and let’s get a lively debate going.


Filed under Robert Resta

10 responses to “Facts, Figures and Fictions in Genetic Counseling

  1. Andy Faucett

    I agree. I think we use numbers as a comfort crutch because we do not like talking about uncertainty. Can a patient really tell the difference between a 10% risk and a 15% risk. I’ve been talking risk for years, and I am not sure I can. Genetic counseling is not simple and I think by relying on numbers, we try to simplify the process rather than have the real discussion needed. I found as I gained experience, I used numbers less. Over the years several patients have told me, “that’s just a number, either I do or I don’t ….”

  2. Meg Eilers

    Thanks for the interesting blog, Bob.

    I have to agree with Andy that the longer I am a genetic counselor, the less and less “numbers” I use with patients…for much the same reasons that Andy and you listed.

    I appreciated your post, because (for example) when I do cancer genetic counseling, I sometimes feel like I might be perceived as doing it “wrong” because I don’t spend hours going through risk assessment models. Of course, “numbers” can be helpful and they are often important to know/understand as a professional, but after working with lots and lots of prenatal couples making decisions, I realized that a long discussion about “exact numbers” wasn’t often the most key factor in a family’s decision making.

    (PS. I also had a chuckle about your “final exam” analogy; I’m often telling my genetic counseling students to remember that for most families, coming to talk to a genetic counselor often feels likes what most of us felt like sitting in organic chemistry class…lots of unfamiliar words and diagrams and facts…and so it’s important to figure out how to get past that to have a more meanful conversation.)

    Thanks again.

  3. Andrea

    This is an interesting topic, and I definitely agree that sometimes we get caught up with numbers that are often times quite arbitrary. I’ve had the same situation with patients saying, “Well the baby either is affected or it’s not,” and a lot of patients feel this way I believe. However, on the other hand, I have also had quite a few statisticians and engineers come in that are so hung up on the numbers and probabilities that sometimes it makes my head spin! They sit in my office and do their mental calculations that I must admit I sometimes have trouble following! In these scenarios, it becomes beneficial to have those numbers to present to patients that work better with numbers, and even with patients that aren’t too caught up in the numbers, I often have questions about probabilities. So while I think we must take care with presenting these risk numbers, and make sure that patients understand they are merely estimates, sometimes I feel that it gives patients something more concrete to wrap their minds around. It just becomes a balance between presenting the information but not making it the sole focus of the session. Of course, I am a newer counselor, so whose to say how I may feel about this topic down the road!

  4. Michelle C

    In defense of numbers, for my serum screen positive patients who are against having amnio (and perhaps shouldn’t have had screening in the first place, but that’s another topic!), if I can tell them their DS risk of 1/127 is essentially more than 99% that the baby is unaffected, at least they can hold on to that figure and have lessened anxiety throughout the rest of the pregnancy. For undereducated people for whom numbers and statistics don’t mean a whole lot, they seem happy with “more than 99% that it’s going to be okay.”

  5. Samantha

    I think a study on engineers in a genetic counseling session would be fascinating! I have been caught up in the “more numbers, please!” fascination of some engineers and it makes me feel like a calculus book, which I am not. When I give out number it comes with a disclamer, “these numbers do not hold true for everyone”.
    As a student and newbie GC, I LOVED numbers, it made me feel like I had knowledge; like I was providing a service which without the numbers would have been wasteful. As I got more experience, I realized that these numbers are silly. They inflate; they deflate. They lie, cheat and steal away from the topic at hand. So, while I still give out numbers to those who ask, I have strayed away from the stats and focused on the effects of test outcome.

  6. Barb

    Your consciousness raising is admirable and long overdue in the profession. Thanks for being a renegade and a hero and asking us to think.
    There are further complexities about numbers in GC even than those you raise:
    1. There are decades of research demonstrating that none of us humans have a conceptual understanding of a number less than 1%. Think about the fractions we offer clients in prenatal counseling. I have taken to stating loosely whether a number is more or less than this (accuracy questionable) because I understand a fraction of 1% is impossible to know. This makes it hard when you are asking people to compare two numbers less than 1%-it’s meaningless. Actually it’s worse than that. Because one is higher it carries more feelings of concern, even when both are slight and we cannot discern an actual difference.
    2. We prefer certain numbers over others. Many cancer counseling sessions focus on numbers estimating the likelihood that a client carries a BRCA1 or BRCA2 mutation without the context of an estimate of the client’s lifetime risk for developing cancer. Isn’t the chances for getting cancer the focus of the counseling? Where is the relevant context? And the age old problem, how do we help individuals decide how to manage the meaning of a population statistic?
    3. A majority of the population is innumerate. That is, they do not think in numbers. Numbers do not represent ideas to them. (Read recent studies on numeracy-fascinating).
    4. When we assign meaning to risk estimates to help clients appreciate their meaning, we use words that mean strikingly different things to different people. What is “low” or “average” to us is not likely to map onto a similar interpretation by a client (or even that of a professional peer). So, when we step away from our wobbly number sources to use qualitative descriptors, we broker in territory that is perhaps even more embedded bias and judgment.
    5. When making decisions, few clients actually use numbers to guide them. Rather, they follow their “gut” or their feelings (often short cuts or heuristics) about whether testing seems like the right thing to do. If a client has a gut feeling that she should test and she is in the lowest possible risk group, should we just follow her lead and “support” her choice. Or, should we say, well, I understand why you might feel that is the right choice for you, but from my perspective, it seems you are willing to take a risk that far exceeds the likelihood that you will learn valuable information?
    6. When I have moved to new places (its been awhile) and learned that the faculty in each location used “different” numbers to represent risks, I would ask where the numbers originated. Similar to your experiences Bob, they most often had no idea. It was like a habit or a tradition and often not supported by data (that I would dig up) in the literature. I found this unsettling in our profession and often ask students why they are using the numbers they give. (It’s usually because that is what the supervisor uses or asked them to use). We all need to understand the sources of our information and evaluate it carefully, throughout our professional years of practice.
    7. Numbers help us retain feelings of control in an environment of brokering in uncertainty. Similarly they sometimes help our clients feel in more control. But this can be a smokescreen for helping clients find successful ways to manage the stress that can accompany the unknown. The lack of guarantees in pregnancy are only a preview to the lack of guarantees in the life of the child. Perhaps we should help new parents to begin that journey.

  7. Vera Cherepakho

    Thank you for all of your thoughts. I think these are excellent points and am happy to see an open dialogue within the gc community about this.

    I just read Jehannine Austin’s paper titled “Re-conceptualizing Risk In Genetic Counseling: Implications for Clinical Practice”. It is a very good paper that is along these lines.

  8. sarah

    I was thinking about the ‘numbers’ dilemma while doing first trimester screening counselling the other day. When you ask ‘Which number is right?’ we have to remember that NO number is ‘right’ or ‘wrong’- we just have a risk indication. And lets face it, if we have a 1 in 200 chance of trisomy or a 1 in 230 chance of trisomy- it’s not that different. But it does give us some indication about what to expect over a person who has a 1 in 5 chance of trisomy. I’m a very visual person and use pie graphs, which take two minutes to do on xcel, to demonstrate the risk. I find seeing the numbers gives people a bit of an idea over the abstract.
    Tabor 2010 gives some good numbers on risks post CVS and amnio as well.
    In the end, it really comes down to a 50% risk each time (As we often joke here at work)…it either happens or it doesn’t!

  9. Pingback: Resta’s Rules of Genetic Counseling | The DNA Exchange

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