6 ms·
>If a test has 50, 75, 90% false positive rates, as many do What tests are you referring to? I can't find a reference but I highly doubt the FDA would approve
by sigmar 10y ago
>If a test has 50, 75, 90% false positive rates, as many do
What tests are you referring to? I can't find a reference but I highly doubt the FDA would approve of many tests with that high of false-positive rates.
- mikeyouse 10y agoYour doubt is misplaced.. At least at the high end. Pap smears have a false negative rate of ~20% and a false positive rate of ~10%. Many doctors are now recommending less frequent tests; http://www.wsj.com/articles/SB125875596169058039 http://www.wsj.com/articles/SB125875596169058039
- sigmar 10y ago10% false positive rate is significantly lower than the quoted "50, 75, 90%"
- LionessLover 10y agoHow about you read the article the entire discussion is about? You will learn what is meant right there.
- Falell 10y agoI think these statistics are claiming '50-90% of observed positives are false', not '50-90% of all tests return false positives'. Suppose 0.1% of the population has a condition and the test for the condition has a 0.5% false positive rate. If administered blindly, most positive tests will be false positives.
- fisherjeff 10y agoI think this is the crux of the article's argument - more people testing more frequently and "blindly" means a whole lot more positive results, most of which will be false.
- sigmar 10y ago>'50-90% of observed positives are false' if ^ is what he means, he should write that. The term "false-positive" has a very clear definition in medical statistics.
- brianwawok 10y agoFair enough. But the more rare a condition, the more observed positives will be false.
- Houshalter 10y agoSuch a test would still be very useful, when combined with other independent weak tests. If 5 weak tests in a row confirm you have cancer, then you should worry. And anyway just report the numbers to the doctor and the patient. "This test has a 5:1 likelihood ratio, so if the odds of you having the disease were 1 to 100, it's now 5 : 100 or 1 to 20." Everyone needs to get a better grasp on probability.
- dragonwriter 10y agoWhich doesn't mean it's not a good test to rule out the tested condition if there are symptoms that might indicate the condition. Sometimes it's clinically valuable to rule out a condition, particularly if the appropriate treatment for another possible condition would be drifter if the tested-for condition might be present. There are people whose training makes them, in principle, the appropriate experts to decide when these tests are needed and worthwhile, they're called physicians.
- deleted 10y ago[deleted]
- pak 10y agoThere's a difference between false positive rate and positive predictive value: https://en.wikipedia.org/wiki/False_positive_rate https://en.wikipedia.org/wiki/False_positive_rate https://en.wikipedia.org/wiki/Positive_and_negative_predictive_values https://en.wikipedia.org/wiki/Positive_and_negative_predicti... The latter depends on the prevalence of the test condition in the population, which is one of the major points of the OP. A test can have a low false positive rate but still have a low positive predictive value if the test condition is sufficiently rare (as it is for most diseases). brianwawok was probably referring to tests with a low positive predictive value.
- sigmar 10y agoAll very true. Perhaps he mistyped, not sure. I'm just pointing out what was written and factually inaccurate.
- tokenadult 10y agoIf you read the fine article, you will see a very clear example of how a highly accurate test can still be misleading for clinical practice if the clinician is deciding whether or not to treat for a low-base-rate condition. Examples like this have been in books about statistical reasoning for medical decision-making over and over and over again since the turn of the century.