There has been some research into whether people who are “normative” (term used in the studies) consider themselves to identify to a greater or lesser degree “as a man” (if female) or “as a woman” (if male).
Depending on the study, IIRC, between 35 - 40% of subjects did not “feel” 100% “as a woman” (females) or “as a man” (males) 100% of the time.
Some trans activist takes on this are that either:
a) even fleeting, partial “feeling as if the opposite sex” means that a person is trans so there are lots more trans people around than people realise.
(However, this goes completely counter to the usual claims by trans activists that anyone who goes the whole hog but then detransitions was never really trans in the first place.)
b) there is no clear distinction between “trans” and “cis”
(So, arguably, neither descriptor makes much sense.)
From the “Crossdreamers” website:
The Multi-Gender Identity Questionnaire
The study is based on what they call the Multi-Gender Identity Questionnaire (Multi-GIQ). The Multi-GIQ includes a lot of variables relevant to gender identity, including:
“feeling-as-a-woman”
“feeling- as-a-man”
“feeling-as-both-genders”
“feeling-as-neither-gender”
“satisfied-being-a-woman/man”
“wish-to-be-a-man/woman”
“dislike-my-body-due-to-its-female/male-form”
“wish-to-have-the-body-of-the-other-sex”
To give you two examples of the type of questions the respondents were given:
In the past 12 months, have you had the wish or desire to be a man
Always, Often, Sometimes, Rarely, Never, Not relevant
In the past 12 months, have you wished you had the body of the “other” sex?
Always, Often, Sometimes, Rarely, Never
From
”More than one third of non-transgender people have had crossgender dreams and fantasies”
Jan 13th 2019
www.crossdreamers.com/2019/01/more-than-one-third-of-non-transgender.html
The author has also commented on the validity of the study given the population sampled:
”Is it true that 1/3 of non-transgender people fantasize about being the other sex?”
crossdreamers.blogspot.com/2019/01/is-it-true-that-13-of-non-transgender.html
There are links to the original research in the references for both articles.