Adult Lifelines participants completed baseline questions on a broad range of topics, enabling researchers from the University Medical Center Groningen to calculate a gender index.

The gender index can be requested in the Lifelines catalogue or by mail (data@lifelines.nl). When this data has been used in your research, you will have to include a reference to the reference paper listed below.

Ballering A.V., Bonvanie I.J., olde Hartman T.C., Monden R., Rosmalen J.G.M. (2020) Gender and sex independently associate with common somatic symptoms and lifetime prevalence of chronic disease. Social Science & Medicine.

Participants had to meet several participants in order to be included in the calculation of the gender index:

• Participant completed the adult baseline questionnaire
• Participants had their DNA analyzed in GWAS
• Participants with no intersex condition or non-conform gender identity

These selections resulted in a subsample of N=13,321 Lifelines participants to construct the gender index.

Additionally, a variable selection was performed. Where the researchers included all psychological and social variables, as long as they met the following two criteria:

• The variable is not reflecting a momentary emotional state that strongly fluctuates over short time periods
• The variable has less than 40% missing values

The included variables (N=153) cover three of the four gender aspects (gender roles, gender dynamics, and institutionalized gender). More detailed information on the selection process can be found in the reference article.

To construct the gender index, selected variables were entered into an elastic net regularized generalized linear model with sex as dichotomous outcome. The participants were randomly assigned to a trainingset (80%) and a testing set (20%). Where the trainingset was used to estimate coefficients and the testing set was used to calculate the model's predictive accuracy.

Estimates of the coefficients (AUC 92%) obtained through the aforementioned regression ultimately formed the basis of the compisite gender idex that was applied to each adult Lifelines participant.

Derivative variable
The resulting variable from this analysis is the gender index. This variable is a continuum, ranging from 0% to 100%, and represents the probability of individual being a woman (higher gender index = more feminine characteristics). Androgyny is indicated by an index of 50%, where equal levels of feminine and masculine characteristics are present.

• Ballering A.V., Bonvanie I.J., olde Hartman T.C., Monden R., Rosmalen J.G.M. (2020) Gender and sex independently associate with common somatic symptoms and lifetime prevalence of chronic disease. Social Science & Medicine.
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