I'm trying to compare ETFs using etfdb.

I saw two ETFs that track identical indexes, but both have very different returns after 5 years:

[IVW][1] 5-year return was 125.43%, with an expense ratio of 0.18%.

[RPG][2] 5-year return was 183.31%, with an expense ratio of 0.35%.

Both of these ETFs track the S&P 500/Citigroup Pure Growth Index.

I was under the impression that ETFs were passively managed, and therefor two ETFs tracking the same index would have the same return, less expense ratios. Is that an incorrect assumption--are (some) ETFs actively managed?

Is there something else that I'm not accounting for which would justify different returns for ETFS tracking identical indices? 


  [1]: http://etfdb.com/etf/IVW/#fundamentals
  [2]: http://etfdb.com/etf/IVW/#fundamentals