Monday, May 23, 2011

Bias in Prognostic Studies

In the evidence-based world every now and again you may come across a paper looking at prognosis. Such papers provide us information on understanding the natural history of a disease or condition, which may then be of use in understanding the nature of your specific patient’s illness (or of those patients who may later relate to the coursework you are teaching now). Knowing something about prognosis allows us to provide information to the patient about predicted outcomes of treatment, and for some conditions (such as, say, the common cold), we know a great deal. Conditions such as back pain are less well understood and therefore rife for discussion in a prognostic paper. But there are several kinds of bias which affect prognostic studies. These include:

Lead Time Bias: this occurs when earlier results related to diagnosis of a condition suggest a treatment effect even though the patient has not, for example, lived any longer. In reviewing studies of prognosis, we need to ensure that our inception cohort had a clearly defined inception point so that they all have the same starting point. Look to see that this is presented in the methods section.

Centripetal Bias: This occurs when a referral center has such a good reputation that it attracts people from outside its geographic location. This then affects the characteristics of the patients that center sees, since, for example, only those who can afford to travel there will be included in an analysis of the patients being seen. Effects or poverty would then be taken out of understanding how this disease progresses.

Popularity Bias: This happens when people with certain specific diagnoses are treated differently than those with other diagnoses or conditions. This may affect the patient flow in a tertiary care center known for its management of that specific condition, affecting the nature of the patients they then see and making them not reflective of the condition at it typically presents in a population.

Referral Bias: This occurs when a select group of patients is referred for study. The problem here is that this leads to that sample not being random or even a reasonable sample of the condition of interest.

Diagnostic Access Bias: If your starting point for conducting a prognostic study requires access to, say, an MRI imaging center, does your community even have one? Does each potential participant in the study have equal access to such a center? Some require referral and some require lengthy waits. This may affect the types of patient seen, making them atypical of the condition of interest.

Diagnostic Suspicion Bias: If the physician can identify the group assignment of a patient, he or she may treat that patient differently.

Expectation Bias: This occurs when a physician second-guesses what is happening in a trial due to prior knowledge he or she may have. The more information about each patient we have, the more our expectations may influence what we do and how we treat the patient, affecting prognosis.

These are sources of error in prognostic studies you should be aware of. Prognostic studies are not common in chiropractic, but are likely to occur in the future.

Monday, May 16, 2011

A few youtube clips that may help you understand EBCP concepts better

1. Risk:
This is a nice little introduction to the concept of risk in medical literature. The author uses a simulated study to help illustrate concepts here.

2. Confidence Intervals: And here is a presentation which clarifies understanding of confidence intervals, another key concept in reading and interpreting medical literature.

3. Sample Size Calculation:
Here the idea is to know how many subjects you need in a study to be able to achieve statistical significance.

4. Regression Analysis:
This is a common procedure used in statistics but not one everyone necessarily understands. This little clip does a nice job of explaining what this is.

5. Evidence-Based Medicine 1:
An introduction to the topic, looking at critical appraisal.

6. Evidence-Based Practice:
This is about the real world applications of EBCP.

7. Research Methods:
A primer on beginning research.

Beyond this, so much more exists on youtube that can help explain concpets related to evidence-based practice, to teaching effectiveness and to scholarship. Poke around, and enter what I have called a "youtube fugue..."

Monday, May 2, 2011

Asking and Answering Questions Effectively in a Public Forum

The latest issue of the Journal of the American Medical Writers Association has a very interesting article about how to ask effective questions in public forms, and how to provide effective answers in return (1). It notes that often we are asked to sit though meetings and programs where we bemoan the fact that audience members ask long and seemingly pointless questions and in response receive even longer and less meaningful answers. We have all seen this happen, and we all sit and try not to squirm when it does. Beyond our discomfort, however, is a more important point: there is supposed to be a successful exchange of information and it has not occurred. Similar to writing, we need to communicate effectively. Krumm’s article provides an overview on making that happen. He provides an overview of 3 related topics in doing so.

First, he brings up the issue of understanding the different types of question. Krumm defines 3 types of questions one may see in a scientific setting. (1) The first is the Specific Question. These are questions which require a categorical answer, such as either yes or no, or a factual answer (and for whom the question usually starts with a wh, such as what, who, where, etc.). (2) Second is the Leading Question. This is an open-ended question requiring an element of analysis, synthesis or evaluation, and they require answers with more in-depth analysis and interpretation. (3) Finally, there is the Presupposition Question. These are questions with assumptions behind them, often critical in nature, and often begin with the word why. These often appear to be, and are, confrontational.

He then looks at asking effective questions. He suggests the following. (1) First, think about the question. Identify what it is you wish to know- broad information or specific. (2) Ask a precise question. This does not mean it must be short, but that it is formulated clearly so that the audience and the presenter easily understand it. (3) Stick to the topic at hand. Make sure your question is related to the discussion at hand. Do not introduce tangential topics. (4) Ask 1 question at a time. Too many questions can make it hard for the presenter to know how to answer and for the audience to follow. If you need to, ask if you can ask a follow-up question. (5) Be careful about “why” questions. These are seen as accusatory and put the presenter on the defensive. (6) Ask your question politely. You should never be rude or confrontational. This is also important when a presenter may have given incorrect information. Follow the Golden Rule. (7) Conversely, do not be overly complimentary; there is no need for a constant stream of praise to a presenter.

For those now in position to answer properly asked questions, Krumm suggests this: (1) Rehearse answers to obvious question. You know what you will be presenting, so anticipate the question you will get and be ready to answer them. (2) Clarify the rules (where appropriate). Let people know when and how you will answer questions. (3) Listen to the question and do not interrupt. Listening is a key skill, and don’t barge in out of impatience. (4) Repeat the question. Not everyone will have heard it. (5) Ask for clarification when necessary. You can politely ask when you are unclear as to what you are being asked. (6) Be honest. If you don’t know the answer, say so. (7) Give short and precise answers. Stick to the point, and remember others want to ask questions as well. (8) Don’t be defensive if the questions are hostile. This is hard to remember, but you can best defuse anger with calm. Remain courteous.

Note: I will be gone for much of next week, and will post again upon my return, May 16. Until then.

1. Krumm P. How to ask effective questions and provide effective answers in a public form. AMWA J 2011;26:21-22