I have a doubt about what will be the right way to use or represent categorical variables with only two values like "sex". I have checked it up from different sources, but I was not able to find any solid reference. For example, if I have the variable sex I usually see this in this form:

id sex 1 male 2 female 3 female 4 male

So I found that one can use dummy variables like this: enter image description here


and also in this way:

enter image description here


Therefore, which one would be more adequate way to deal with this variable, for example, in a classification system. I am inclined to go with the dummy variables, but I would like some opinion about it.



2 Answers 2


This case can be simplified with a single boolean feature because the original variable sex is binary: it can only have values male or female.

This implies that the two values are complementary of each other, so there is no need to keep both: $X_1$ contains exactly as much information as keeping both sex_male and sex_female.

Note that this simplification cannot be done as soon as the categorical variable can have more than two values.

Side note: sex is not always a binary variable anymore, many surveys would propose a third options such as "doesn't identify as binary".

  • $\begingroup$ thank you for your reply, please could you expand your last part in which you mention the third option? $\endgroup$
    – Lila
    Commented Jul 19, 2021 at 16:04
  • $\begingroup$ @Lila this is a recent social change, it's not related to data science: surveys often give several choices, for example 'non binary' additionally to male and female. For example the SO survey asks about gender with many choices: man, woman, "gender queer or gender non-conforming", "non-binary". $\endgroup$
    – Erwan
    Commented Jul 19, 2021 at 20:17

There are three encoding options you can utilise for your scenario of sex(gender)

  1. One hot Encoding: Here each category is mapped to binary variable containing either 0 or 1.Widely utilized when features are nominal.
  2. Dummy Encoding: similar to one hot encoding. While one hot encoding utilises N binary variables for N categories in a variable. Dummy encoding uses N-1 features to represent N labels/categories
  3. Effect Encoding: Also known as deviation encoding or sum encoding. Similar to dummy encoding, however 3 values are used(1,0,-1)

Do look into Encoding Categorical Variables

Do note that gender identity is not always binary(0 or 1)

There are many different gender identities, including male, female, transgender, gender neutral, non-binary, agender, pangender, genderqueer, two-spirit, third gender, and all, none or a combination of these.

  • 1
    $\begingroup$ Some of the text looks similar to analyticsvidhya.com/blog/2020/08/…: "Here each category is mapped to binary variable containing either 0 or 1" vs "Each category is mapped with a binary variable containing either 0 or 1."; "Dummy encoding uses N-1 features to represent N labels/categories." Please make sure to provide proper attribution for your sources. $\endgroup$
    – D.W.
    Commented Jan 1, 2022 at 22:38

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