Much to many believers’ and atheists’ chagrin, there are few things in religion that could provide quantitative evidence about religion’s claims. Christianity does make one claim, though, that I think is quantifiable: the workings of the Holy Spirit.
It all began back on a first-century Pentecost:
When the day of Pentecost came, they were all together in one place. Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them. (Acts 2.1-4)
Most Christians believe that through the power of the Holy Spirit, baptized believers are able to do things they wouldn’t otherwise be able to do. If you look at references to the Holy Spirit in the Bible, it generally seems to be providing peace and wisdom. The Holy Spirit is supposed to dwell within believers, making them new creations and such.
Wouldn’t that have an effect?
Take a country like Poland, where 97% of the population claims Catholicism as their religion, and I’d say closer to 99% have been baptized. If there was any truth to the claim that the Holy Spirit’s indwelling somehow makes a difference, it should show up statistically in a country where 99% of its inhabitants experience that “indwelling.” The crime rate should be lower; corruption should be rarer; evidence of love for fellow humans should be abundant. But that’s not the case. Indeed, the crime rate in Poland is just about the same as any other country in Europe; corruption in Polish politics exceeds the level of other European countries; and Poles clearly show love of fellow humans about as often as any other group of people (read: not very).
Apologists would claim that there are many other factors at work here and rightly point out that there is an element of free will in all humans. However, I’m not expecting the Holy Spirit to create a paradise; I’d be satisfied to see some small statistical difference.