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Detection Bias

by Raywat Deonandan, PhD
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    00:00 that we're seeking.

    00:02 The next kind of bias is my personal favorite, that's detection bias, because detection bias results a lot in surveillance studies. This is when the act of looking for an effect erroneously gives you the impression that an effect actually exists or that it is larger than it actually is. So imagine you have a phenomenon and you're looking for that phenomenon, are you going to find it, yes you are, by the very act of looking for it, you're going to find it. That doesn't mean it suddenly arose, it might have been there all along, so your presence there has an effect on how you view the data collection process. So here is an example, let's say doctors are more likely to examine obese patients for diabetes than they do thin patients, we know this to be true because we know that obesity is a risk factor for diabetes, therefore they're more likely to find diabetes amongst obese patients than they are in thinner patients.

    01:00 This gives rise to something called a syndemic. A syndemic is when we have an epidemic that's based on synergy between two different diseases, in this case diabetes and obesity. It might be true, it might not. But it's entirely conceivable that it will give you a skewed impression of the prevalence of a certain kind of condition in a certain kind of person. My personal favorite is this graph that I show all my students. So this shows us the new AIDS cases per year from 1990 till about 2000 in three different regions in the world; Latin America, the Caribbean and North America. In North America the new AIDS cases declined in the early to mid-1990s, we think due to new therapies being introduced and in the Caribbean in the same time period the number of AIDS cases increased dramatically. And I always asked my students, why was that? Why do you think it went up so dramatically in the Caribbean? And I hear all sorts of theories, things like, "Oh! because there are more travelers were coming in from different AIDS endemic areas." or the rate of sex work increased or a variety of different kinds of theories. In truth, what was happening in the Caribbean is we started looking for more AIDS cases, so we found more AIDS cases, it was always high, but we only noticed it in the late 1990s, so that graph has the appearance of an increase, but there wasn't an increase, that's classic detection bias.

    02:28 So what have you learned? You have learned what the typical kinds of information bias


    About the Lecture

    The lecture Detection Bias by Raywat Deonandan, PhD is from the course Statistical Biases.


    Included Quiz Questions

    1. Detection bias
    2. Confirmation bias
    3. Misclassification bias
    4. Response bias
    5. Reporting bias
    1. Reporting bias
    2. Confirmation bias
    3. Misclassification bias
    4. Observer bias
    5. Response bias
    1. Confirmation bias
    2. Reporting bias
    3. Misclassification bias
    4. Observer bias
    5. Response bias

    Author of lecture Detection Bias

     Raywat Deonandan, PhD

    Raywat Deonandan, PhD


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