I thought I had blogged on this paper before, but I can’t find a prior post. So, here are some quotes and brief comments on Zeliadt, S. B., Ramsey, S. D., Penson, D. F., Hall, I. J., Ekwueme, D. U., Stroud, L., & Lee, J. W. (2006). Why do men choose one treatment over another? Cancer, 106(9), 1865-1874.
In the largest study we reviewed, which involved 1000 patients, approximately 42% of patients defined an effective treatment as one that extended expected survival or delayed disease progression, whereas 45% indicated that effectiveness meant preservation of quality of life (QOL).5 This is in contrast to physicians, 90% of whom defined effectiveness as extending expected survival. In another study, fewer than 20% of patients ranked either “effect of treatment on length of life” or “chances of dying of cancer” as 1 of the 4 most important factors in making a decision.26 In 1 study of health state preferences, 2 of 5 men were unconditionally willing to risk side effects for any potential gain in life expectancy.64 These studies suggest that there is substantial variation in the significance that patients place on cancer eradication, and that treatment efficacy means more than “control” of the tumor for many patients.
Concerns regarding cancer eradication appear to correlate directly with aggressiveness of therapy, with radical prostatectomy being the choice preferred by the majority of patients who focus on cancer control.
So, concerns about cancer relate to treatment choice. To the extent that those attitudinal factors also relate to outcomes (e.g., through their relationship with care for other conditions), they are good candidates for unobserved factors that, in part, explain the difference between results of instrumental variables (or RCT) and other observational study techniques.
Side effects like incontinence and impotence are frequently cited concerns, as reported in the paper. However:
To our knowledge, there is limited information available regarding how men balance side effects in making their treatment decision. For example, although preservation of sexual function was rated as very important by 90% of men age younger than 60 years, and 79% of men age 75 years and older, in a separate question only 3% of these same men indicated that “having few side effects” was the most important consideration in initiating therapy.5 Fear of side effects was also stated by only 3% of men in a study in North Carolina, in which the majority of patients were black.8 Srirangam et al.45 reported that although 55% of spouses reported that side effects were important, only 6% indicated that side effects were deciding factors. One study comparing surgery and brachytherapy reported that 25% of patients chose between these 2 options based on the side effect profile.9 In addition, although Holmboe and Concato10 found that 49% of patients were concerned with incontinence and 38% were concerned with impotence, only 13% reported weighing the risks and benefits of treatment. These studies demonstrate the apparent disconnect between patients’ stated importance of side effects and the role that they actually play in reaching the final treatment decision.
Ultimately, it’s what patients actually do, not what they say, that matters. Therefore, side effects may be less of a relevant factor in treatment decisions than is commonly believed. Put another way, that something is a concern doesn’t imply that it changes one’s decision. That does not take away from the fact that concerns are psychologically important.
Less frequently discussed are concerns about other potential complications.
Fear of surgical complications was emphasized by some men who selected watchful waiting. 7 A different study found that complications due to surgery were of concern to 12% of patients when considering surgery.3 A belief that radiation is harmful rather than therapeutic was offered by some men who selected surgery.44 When considering radiation therapy, 21% of men indicated concern about skin burns.3 Long recovery times were cited by 17% of patients.10 For a small percentage of men, issues such as fear of surgery or radiation appeared to be the primary factor in their decision regarding treatment.
One reason complications and side effects may play a relatively small role in treatment decisions is that physicians are playing a large role in influencing those decisions.
The role of the physician recommendation has received considerable attention in prostate cancer decision making due to the widely recognized preferences held by each physician specialty. As might be expected, opinions regarding the optimal treatment for localized prostate cancer vary among urologists, radiation oncologists, oncologists, and general practitioners. Urologists nearly universally indicate that surgery is the optimal treatment strategy, and radiation oncologists similarly indicate that radiation therapy is optimal.78
To the extent that treatment choice is driven by physicians and is otherwise unrelated to outcomes, it suggests an opportunity for a valid instrument. This is what Hadley, et al. exploited.
The paper continues with an exploration of the role of family members, race, socioeconomic, and psychological factors in treatment choice. Some of these (e.g., family relationships, socioeconomic factors, psychological factors) are likely to be incompletely observed and are, therefore, additional possible reasons why instrumental variables and RCT results differ from naive, observational studies. They key is that they may also be related to outcomes. It’s not too hard to imagine they could be.
[Originally posted at The Incidental Economist]