Clinimetrics corner: the many faces of "selection bias"

Now, selection and bias are both nouns. Selection is an uncountable noun and a countable noun. Bias is a countable noun. So, can I put "a" before "selection" on the basis of that it is uncountable? Or I will put it on the basis of the second word, bias? (selection) or the second one (bias). Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3101070/

Another thing I want to ask is that if there is a noun phrase containg two words, does the selection of an article depend on the first word of the noun phrase?

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    The fact that "selection" is an uncountable noun in other contexts is irrelevant here, where it simply functions as an "adjective" modifying the "head noun" bias. And that "adjective" might not be present in the first place, so ask yourself if you'd be prepared to write "...the many faces of a bias" (I wouldn't, but I don't really understand what you're trying to say, anyway), Commented Oct 26, 2023 at 11:32
  • ...but I could talk about the many uses of a jug, OR the many uses of a water jug, which looks to me like another "uncountable noun and a countable noun" pairing on a par with yours. Commented Oct 26, 2023 at 11:35
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    My favourite "selection bias" example at the moment: Why are iron levels different in the left and right hands? Commented Oct 26, 2023 at 11:39
  • @AryenduKumar Please provide an example sentence. Commented Oct 26, 2023 at 11:50
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    @FumbleFingers, off topic, but I love the hæmoglobin anecdote. A wonderful cautionary tale for careful reasoning. Commented Oct 26, 2023 at 15:38

1 Answer 1


Selection bias is a compound noun. For compound nouns that are made up only of nouns, only the final noun is ever pluralised, so you can have egg sandwiches, but you can't have eggs sandwich.

The countability of a compound noun is therefore based only on the final noun.

In your example, bias is the final word, and it is normally countable (though, as the link I provided shows, it can also be uncountable), so you can have selection biases or a selection bias.

  • Bias is countable but can I also have no article before 'selection bias' ? Will the justification be - It will give a general meaning. Commented Oct 27, 2023 at 2:42
  • @AryenduKumar my bad, I didn't consider the uncountable usage. Yes, It would relate to bias in general.
    – JavaLatte
    Commented Oct 27, 2023 at 7:16
  • @Then, Mnay time I have seen that sentences like above, second word is singular and countable. and the first word is uncountable and as per the rule there should be 'a' or 'an' but there is no article ... Why ? Commented Oct 27, 2023 at 7:25
  • can you provide examples?
    – JavaLatte
    Commented Oct 27, 2023 at 7:47
  • Do not remeber, please explain from the context of "selection bias" Commented Oct 27, 2023 at 8:16

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