A research idea I had was comparing toilet training ages with the following variables in countries that have diverse, heterogenous populations that allow us to get a representative sample of multiple different demographics:
1. Parental age
2. Number of children in household
3. Household income
4. Religious affiliation
5. Political alignment
6. Family structure: single vs married parents, two incomes vs one income, presence/absence of other family members in the child's life, etc
7. Immigrant vs natural born status of the parents
I hypothesize that earlier toilet training age would be associated with parents who are older, are not considered high income, identify as being more devout in faith, and have other family members present in the life of their child.
People say that when parents have less time on their hands due to working long hours keep their kids in diapers longer, but I think that it depends on their socioeconomic standing. Diapers are EXPENSIVE. A single parent working an ungodly amount of hours at a low earning job has an immense economic pressure to get their child out of diapers as fast as possible, whereas a married couple of high earners who work long hours, like an investment banker married to an emergency physician, would be able to afford to keep their child in diapers for as long as they would like. While daycare may attempt to train a child, if there's no continuity between school and the home, the child will not be trained.
I also feel like religious beliefs play a role here too. For example, Islam is obsessed with cleanliness. This goes beyond people who are devout, practicing Muslims. My (Iranian) family is not religious, but my mom raised me with an obsession on being clean. I was raised to never sit on the ground, put my hands on the ground, eat any food that had fallen on the floor, or share a cup/straw/bottle with anyone. When I went to school and was told to do push ups/sit ups on the blacktop, sit down on the multipurpose room floor during school assemblies, and saw my friends eating stuff that had fallen on the ground, I was aghast. I basically got culture shock in my own country (USA). This obsession over cleanliness extends to toilet training. Diapers are seen as a necessary evil and there's massive societal pressure to get kids into underwear ASAP. I feel bad for all the kids abused in Iran because of their parents' desire to save face in front of the family. Goodnites and their equivalents do not exist in Iran. Heck, pull ups for toilet training didn't exist until the mid 2010s, and that was just because of a desire for families to look Western. The idea of your 12 year old son wearing a diaper to bed because he wets the bed is incomprehensible to Iranians. They blame the child instead. Even in Qatar I couldn't find boys Drynites 8-15 at Carrefour. They had the girls version, but not for boys. I saw a map at the beginning of the pandemic of a study done in Europe asking people if they regularly wash their hands after using the toilet. The Christian countries had shockingly low percentages of yes responses, but Turkey and the Muslim countries in the Balkans had over 99%. I think in the Netherlands half of people said yes and half said no.
I will not comment on the political alignment variable due to forum rules, although I do have a prediction. And no, it's not a dichotomous "left this, right that" prediction.