In a second step, they could answer an optional 30-item part (concerning past relationships and preferences for physical features)

The study design was a cross-sectional online survey implemented in the survey software Typeform v2 ( The study was online from . Subjects were told that the survey was about the qualities of their ideal partner(s). Participants younger than 18 were not able to participate in the survey. All participants completed a 14-item section focusing on demographic information and long-term preferences. In a third part, participants could answer questions about potential short-term partners, if they were willing to do so. Ten parallel language versions of the survey were developed: Chinese, Danish, English, French, German, Italian, Footnote 3 Japanese, Portuguese, Russian, and Spanish. Translators were native speakers of their respective languages who were contracted by the menstrual cycle tracking app Clue on a regular basis. A “four eyes” approach (one translator and one proofreader per language) was used. The survey was advertised via email campaigns to the respective user bases, messages within the Clue app, and social media channels.

Exclusion Variables

Exclusion criteria as outlined below were based on the following variables. Gender was measured with a categorical item “Do you identify as…” with response options (a) Woman, (b) Genderqueer/Nonbinary, (c) Man, (d) None of the above, (e) Prefer not to say, and (f) Other. Sexual orientation was measured with a categorical item “How would you describe your current sexual orientation?” with response options (a) Straight/Heterosexual, (b) Lesbian/Gay/Homosexual, (c) Bisexual/Pansexual, (d) Queer, (e) Asexual, (f) Prefer not to say, and (g) Other. Relationship status was based on the item “Select your relationships during the past 3 months” with response options (a) No romantic or sexual relationships during the past 3 months, (b) Short-term (casual) sexual relationship (e.g., hookups or one-night-stands), (c) New (less than 1 month old) romantic and/or sexual relationship, (d) Ongoing (longer than 1 month) uncommitted/nonexclusive romantic and/or sexual relationship, (e) Long-term committed/exclusive sexual relationship with one or more partners, and (f) Other. Multiple options could be chosen. Participants who chose response options (c), (d), (e), and/or (f) were treated as non-single. Seriousness was assessed with the categorical item “We understand that sometimes people fill out questionnaires for fun and give answers that may not be accurate. In the interest of scientific accuracy, we will exclude those responses from our final analysis. Please choose one of the statements below” with response options (a) I took the survey seriously; please use my information in the study, (b) I did not answer seriously; please disregard my information, and (c) I choose not to answer.

Variables Included in Analyses

Age was measured with one item asking “How old are you?” and participants answered with an integer number. Age was not restricted to a certain number; values higher than 100 were set to missing (affecting 15 participants in the raw dataset and 5 participants in the dataset after exclusion). Footnote 4 All other variables and item wordings are listed in Table 2.

All importance items were measured on a scale from 0 = not at all important to 6 = very important. All level items were measured on a scale from (e.g.) 0 = not kind to 6 = very kind. Level of parenting intent was measured on a scale from 0 = does not want to 6 = very much wants. For each attribute, participants were only asked about the desired level if they had indicated an importance of at least 1. This means that participants who had indicated an importance of 0 were not asked about the desired level, implying a smaller sample size for those analyses. For the preference attributes, we calculated five dimensions using the mean of two items: Kind-supportive included the variables kind and supportive (r_importance = .24 [99.5% CI: .22, .26]; r_level = .28 [.26, .30]); Footnote 5 attractiveness included attractive face and attractive body (r_importance = .62 [.61, .64]; r_level = .59 [.57, .60]); financially secure-successful included financially secure and successful/ambitious (r_importance = .34 [.32, .36]; r_level = .35 [.33, .37]); confident-assertive included confident and assertive (r_importance = .29 [.27, .31]; r_level = .32 [.30, .34]); intelligence-educated included intelligence and educated (r_importance = .43 [.41, .45]; r_level = .46 [.44, .48]). We calculated all five dimensions separately for importance and for level ratings.