What is more likely?

[Eway]

"About 80% of the UK population has had toxoplasmosis and developed antibodies; this is more likely to be the case the older a woman is."

What does "this" refer to?

[rewboss]

I think "this" refers to having toxoplasmosis and developing antibodies. But it's hard to say for definite; I think the paragraph the sentence is in may be poorly organised. It's especially confusing because of what we know about the real world: we know that the population of a country like the UK is likely to be roughly 50% male and 50% female, but the first clause mentions 80% of the whole population, and the second clause mentions only women.

Do you have the rest of the paragraph for us to see?

[Eway]

Yes. Hope this would be helpful:

"Certain foods can become contaminated and be a risk for pregnant women. Toxoplasmosis can cause miscarriage and is usually contracted by coming into contact with the faeces of infected wild or domestic animals. About 80% of the UK population has had toxoplasmosis and developed antibodies; this is more likely to be the case the older a woman is. Symptoms develop two to three days after infection."

[rewboss]

Hmm. I think this paragraph needs to be re-organised.

I think my original guess was probably right. Let me try to summarize the paragraph:

1. Some foods can become contaminated with toxoplasmosis.
2. Toxoplasmosis can cause miscarriage.
3. After the first time you get toxoplasmosis, you become immune to it.
4. The older a woman is, the more likely she is to be immune to toxoplasmosis.

It's badly written because the focus of attention shifts several times: from pregnant women, to all UK citizens, then to women in general, and finally the progress of the infection.

[MikeNewYork]

Hmm. I think this paragraph needs to be re-organised.

I think my original guess was probably right. Let me try to summarize the paragraph:

1. Some foods can become contaminated with toxoplasmosis.
2. Toxoplasmosis can cause miscarriage.
3. After the first time you get toxoplasmosis, you become immune to it.
4. The older a woman is, the more likely she is to be immune to toxoplasmosis.

It's badly written because the focus of attention shifts several times: from pregnant women, to all UK citizens, then to women in general, and finally the progress of the infection.

It would probably be clearer with more context. Toxoplasmosis is hardly ever a concern in men. The infection is a serious problem in fetuses, so the concern is high in pregnant women. Many women get themselves checked after they find out they are pregnant. At that stage it is impossible to tell if they have the infection or just antibodies from a prior exposure. The paragraoph in question is explaining that the antibody is most likely due to previous exposure and that the likelihood of innocent antibody detection increases with a woman's age.