4 ms·

From other sources (https://www.medscape.com/viewarticle/891491 https://www.medscape.com/viewarticle/891491) I was able to find they had a specificity of >99%,

From other sources (https://www.medscape.com/viewarticle/891491 https://www.medscape.com/viewarticle/891491) I was able to find they had a specificity of >99%, with a sensitivity averaging 70% but was as low as 20% on certain cancers (esophageal cancer). With such an excellent specificity this sounds promising as a cheap screening tool, although the sensitivity is too low in some cancer types to be used as a means to rule out cancer.

tischler 9y ago
As a reminder: true positive rate (TPR, a.k.a. hit rate, recall, specificity) TPR = TP / P = TP / (TP + FN) specificity (SPC) or true negative rate SPC = TN / N = TN / (TN + FP)
- kmmlng 9y ago
  You labelled both TPR and TNR as "specificity". True positive rate should be sensitivity.
  - tischler 9y ago
    Oops, thanks. I've always had struggle remembering these terms because they are so confusing. "Specific" means that something only relates to one particular element X in a set of more than one thing. Given that meaning, one would expect specificity to mean "how good is the test at correctly reporting the thing it is designed to report X rather than confusing a different thing (an element from the complement of X) for X", but that is sensitivity. Instead, specificity means that with respect to the complement: "how good is the test at correctly reporting all the other elements in the set ¬X as negative rather than confusing an element from ¬X for X". "Sensitive" has a clearer intuition: For example when you want to detect a weak signal, then if your antenna is more sensitive, you can better pick up the signal, thus you are better at telling whether the signal is really there (you have a better true positive rate). I cannot think of a better name for TNR, though, other than simply sticking with TNR and TPR.
    - kmmlng 9y ago
      Your sensitivity intuition is a fantastic way to remember it. I had to look it up myself, but hopefully this will finally make it stick :)
tansey 9y ago
The problem with the idea of cheap screening tools is Bayes' theorem. If doctors go ordering this for most people since it's just a blood test, and if only 1% of people ever really have cancer when tested then the 1% false positive rate means there's only a 50/50 chance you have cancer given the test is positive.
- rplnt 9y ago
  So that's one "wasted" advanced screening for one where cancer is found. That seems great to me. Also, I assume it would be mostly done on higher risk patients (certain work conditions, certain age, etc..). Only once in couple of years on younger population for example. Or if it's really cheap everyone could get it and then there could be more focused blood screening done next so you don't have to get full body cat scans.
  - vidarh 9y ago
    It's not that simple. If the worst effect was some unnecessary secondary screening, it would be a no-brainer. But first of all you need to account for the negative effects of a false positive, and they are much worse than that. They include anything from stress and psychological effects, cost and risks of all the additional screening, to the much worse issue that you also need to account for the fact that for some cancers in some instances it will be hard enough to determine if the growth is malignant in the sense that some proportion of cancerous growth will never pose a threat to the patient, but once diagnosed there tends to be a strong pressure to treat. As a result too frequent screening will save some, but will also result in a large amount of unnecessary chemo, radiation therapy and/or surgeries - all of which come with risks in addition to the pain and discomfort. Then you need to account for frequency of testing. A 1% false positive rate per test looks distinctly worse if the test is repeated every year for a 10-20 year timespan, for example. Then you'll also want to account for how much it improves outcomes. If the cancers it detects are ones that would generally be detected in time anyway, and/or have low mortality, and where treatment outcomes are good, the incremental improvement would not necessarily be big enough to justify the negatives. For breast cancer, for example, there has in recent years been a push to reduce large scale routine mammogram screening because it's not clear if it does more good than harm for many groups of patients (in large part because it leads to overtreatment). This article goes into some of the issues related to that in some detail (and presents both proponents and detractors of large scale screening): http://www.healthbeatblog.com/2009/04/mammography-screening-a-double-edged-sword/ http://www.healthbeatblog.com/2009/04/mammography-screening-...

tischler 9y ago

As a reminder: true positive rate (TPR, a.k.a. hit rate, recall, specificity) TPR = TP / P = TP / (TP + FN) specificity (SPC) or true negative rate SPC = TN / N = TN / (TN + FP)

kmmlng 9y ago
You labelled both TPR and TNR as "specificity". True positive rate should be sensitivity.
- tischler 9y ago
  Oops, thanks. I've always had struggle remembering these terms because they are so confusing. "Specific" means that something only relates to one particular element X in a set of more than one thing. Given that meaning, one would expect specificity to mean "how good is the test at correctly reporting the thing it is designed to report X rather than confusing a different thing (an element from the complement of X) for X", but that is sensitivity. Instead, specificity means that with respect to the complement: "how good is the test at correctly reporting all the other elements in the set ¬X as negative rather than confusing an element from ¬X for X". "Sensitive" has a clearer intuition: For example when you want to detect a weak signal, then if your antenna is more sensitive, you can better pick up the signal, thus you are better at telling whether the signal is really there (you have a better true positive rate). I cannot think of a better name for TNR, though, other than simply sticking with TNR and TPR.
  - kmmlng 9y ago
    Your sensitivity intuition is a fantastic way to remember it. I had to look it up myself, but hopefully this will finally make it stick :)

tansey 9y ago

The problem with the idea of cheap screening tools is Bayes' theorem. If doctors go ordering this for most people since it's just a blood test, and if only 1% of people ever really have cancer when tested then the 1% false positive rate means there's only a 50/50 chance you have cancer given the test is positive.

rplnt 9y ago
So that's one "wasted" advanced screening for one where cancer is found. That seems great to me. Also, I assume it would be mostly done on higher risk patients (certain work conditions, certain age, etc..). Only once in couple of years on younger population for example. Or if it's really cheap everyone could get it and then there could be more focused blood screening done next so you don't have to get full body cat scans.
- vidarh 9y ago
  It's not that simple. If the worst effect was some unnecessary secondary screening, it would be a no-brainer. But first of all you need to account for the negative effects of a false positive, and they are much worse than that. They include anything from stress and psychological effects, cost and risks of all the additional screening, to the much worse issue that you also need to account for the fact that for some cancers in some instances it will be hard enough to determine if the growth is malignant in the sense that some proportion of cancerous growth will never pose a threat to the patient, but once diagnosed there tends to be a strong pressure to treat. As a result too frequent screening will save some, but will also result in a large amount of unnecessary chemo, radiation therapy and/or surgeries - all of which come with risks in addition to the pain and discomfort. Then you need to account for frequency of testing. A 1% false positive rate per test looks distinctly worse if the test is repeated every year for a 10-20 year timespan, for example. Then you'll also want to account for how much it improves outcomes. If the cancers it detects are ones that would generally be detected in time anyway, and/or have low mortality, and where treatment outcomes are good, the incremental improvement would not necessarily be big enough to justify the negatives. For breast cancer, for example, there has in recent years been a push to reduce large scale routine mammogram screening because it's not clear if it does more good than harm for many groups of patients (in large part because it leads to overtreatment). This article goes into some of the issues related to that in some detail (and presents both proponents and detractors of large scale screening): http://www.healthbeatblog.com/2009/04/mammography-screening-a-double-edged-sword/ http://www.healthbeatblog.com/2009/04/mammography-screening-...