Which of the following statements about gender and migration are correct?

1. De facto female-headed households occur when men migrate for work, leaving women in charge but often with limited resources.
2. De jure female-headed households emerge primarily due to widowhood, separation, or being unmarried, compelling women to migrate for survival.
3. Intersectionality in migration research solely examines the economic factors influencing migration.
4. Gender selective migration can lead to an increase in female-headed households in urban areas.