While Intercept is not an Amgen (NasdaqGM: AMGN) or Celgene (NasdaqGM: CELG) in terms of market cap heft, its surge Thursday underscores the importance of investors taking even just a few minutes to study their ETFs’ holdings.

The Intercept scenario also highlights the importance of identifying key differences between ETFs that offer exposure to the same sector or industry group. That endeavor is particularly important with biotech ETFs because in a given year, markets may favor large-cap biotechs over their small-cap brethren or vice-versa.

For example, IBB and BBH, both large-cap heavy, were 2013’s best biotech ETFs, but in2012, BBH was the leader while FBT and XBI both outpaced IBB. In 2011, IBB was the best biotech ETF while XBI held top honors in 2008.

SPDR S&P Biotech ETF