CAPCITY:

• STRENGTH:

  • One strength of Jacobs' study is that it has been replicated

  The study is a very old one and early research in psychology often lacked adequate controls.

  For example, some pp digit spans might have been underestimated because they were distracted during testing (confounding variable). Despite this, Jacobs' findings have been confirmed by other, better controlled studies since (e.g. Bopp et al 2005)

  This suggests that Jacobs' study is a valid test of digit span in STM
• LIMITATION:

  One limitation of Miller's research is that he may have overestimated

  STM capacity.

  Cowan (2001) reviewed other research and concluded that the capacity of STM is only about 4+-1 chunks

  This suggests that the lower end of Miller's estimate (five items) is more appropriate than seven items.