<prompt> Human: Hi guys,For the past two years, my IRA and some of my 401K is currently investing in the SP 500. My IRA is with an ETF, and my 401k in a general index fund. Its gotten me better than average returns so far, especially with the 2017 economy. Ive only been investing the last two years. My question is, from the general advice that Ive received, why do folks generally recommend funds to track the SP 500, and not the DOW or the NASDAQ? Is there something about the former that makes it more desirable?Appreciate any answers and clarification!  <response>: DJIA has only 30 companies and is price-weighted.NASDAQ Composite can only include securities traded on NASDAQ duh. NASDAQ 100 is heavy on tech.SP500 is almost entirely the largest cap weighted and easily traded 500 companies regardless of sectors or what exchange its traded. 