saab, a connection, or correlation, does not indicate cause. Cold snowy nights do not cause pregnancies.
On cold snowy nights more couples might stay home. The more couples stay home, the more frequently they might have intercourse. The more often unprotected intercourse occurs, the higher the pregnancy rate. The higher the pregnancy rate, the higher the birth rate.
But, the cause
of pregnancies is sexual intercourse. Increased frequency of sexual intercourse causes
a higher pregnancy rate. A higher pregnancy rate causes
an increase in birth rate.
The weather doesn't cause increases in birth rate any more than the stork brings babies. It simply correlates with an increased birth rate. Conception is still caused by a sperm fertilizing an egg.
That's why we have to be careful when evaluating research results. In a lot of cases they are reporting an "association" or a correlation. But that can be misleading when it comes to knowing if A is actually causing B.
Hm, we have more babies in Sweden than in Italy.
We also have more snow - don´t you think there might be a connection between the cold snowy nights and babies?
Well, suppose we also find that Italians consume significantly more pasta than do Swedes, and Italians have a lower birth rate than Swedes. So, we have a correlation between pasta consumption and birth rate. Should we then conclude that the consumption of pasta causes a decreased birth rate? That something about pasta interferes with conception?
That's the problem with correlations. They may, or may not, be actually connected to causality--whether one thing actually causes another--and they can be misleading.