A lot of children who refuse to poop in the toilet during training are also constipated—but it's not clear what comes first, the constipation or the training problems. Researchers at the University of Pennsylvania tried to resolve this chicken-or-the-egg debate.

What the researchers wanted to know: Does a child refuse to go because he's constipated, or does he become constipated because he keeps refusing to go?

What they did: Families of 408 consecutive toddlers visiting the office of one of the authors were invited to take part (406 agreed, and 380 went through the study). The researchers monitored the children's progress from the age of 17 months to 19 months until they either refused to defecate in the toilet or finished toilet training (only training for the daytime). The original idea of the study was to test a way to prevent refusal—praising the kid more for pooping, and not being negative about feces—which didn't work. Every two or three months, researchers called the parents and interviewed them again about the child's potty habits and constipation.

What they found: Constipation was much more common in kids who at some time refused to poop in the toilet—70 percent compared with only half of the children who never refused. But which came first? Of those 70 percent, which represents 61 children, 58 were constipated first. So the refusal isn't causing the constipation.

What it means to you: Maybe if the kid's constipation was being treated, he wouldn't be as likely to refuse to go in the toilet.

Caveats: The kids all came from the same pediatric practice. The results depend on parents remembering their children's constipation. And there might be other factors of toilet training that contribute to constipation.

Find out more: The American Academy of Pediatrics offers advice on toilet training.

Some toilet training advice: http://www.motherofallbooks.com/

Read the article: Blum, N.J., Taubman, B., and N. Nemeth. "During Toilet Training, Constipation Occurs Before Stool Toileting Refusal." Pediatrics. June 2004, Vol. 113, No. 6, pp. e520–e522.

Abstract online: http://pediatrics.aappublications.org/