Since the FTSE 100 (INDEXFTSE: UKX) was created in 1984, it has risen around sixfold. For many investors, this may seem like a superb return, since it works out as an annualised growth rate of around 5.7%. When dividends are added, it’s clear that buying shares in FTSE 100 companies in 1984 could have led to high-single-digit returns over the last 32.5 years.

However, the fact remains that an investor across the pond would have done much better than his/her UK counterpart since 1984. That’s because the S&P 500 is now trading around 12.7 times higher than it was 32.5 years ago. This works out as an annualised gain of 8.1% and when dividends are added, equates to a double-digit return over the period. As such, buying the S&P 500 has been a much, much better move than buying the FTSE 100 over a very long time period.

Clearly, it could be argued that today such discrepancies in performance are less likely due to globalisation. In other words, with the world’s economies now being more interconnected, the scope for significant outperformance by one major index over another is less likely. Furthermore, with the FTSE 100 and S&P 500 both being made up of mostly international companies, their performance today and in the next 32 or so years should be much more similar.

However, this idea doesn’t appear to have been borne out in recent months and years. For example, since the turn of the year the S&P has outperformed the FTSE 100. And it was the same story in 2015, 2014, 2013 and over the last decade, with the S&P 500 easily beating the FTSE 100.

Tables set to turn?

Of course, the future is never exactly the same as the past and many investors could argue that the tables will now turn, with the FTSE 100 having greater potential than the S&P 500. That’s at least partly because any asset that goes up more than another is likely to become overvalued relative to its comparator.

For example, the S&P 500 has a yield of around 2.2%, while the FTSE 100’s yield currently stands at over 4%. This indicates that the FTSE 100 is much cheaper than its US peer, and so could benefit from a faster upward rerating than the S&P 500 over the coming years. And with the FTSE 100 containing a greater proportion of resources companies than its US peer, a continued surge in the prices of oil and other commodities could help reduce the gap in performance between the two indices.

In terms of their long-term performance, both the S&P 500 and the FTSE 100 continue to offer upbeat growth prospects. However, with the FTSE 100 being so much cheaper than its US counterpart, it may prove to be the winning buy over the coming years. As such, selling the FTSE 100 to buy the S&P 500 doesn’t seem to be a shrewd move at the present time.

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Peter Stephens has no position in any shares mentioned. The Motley Fool UK has no position in any of the shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.