I believe both you and parent are correct. What about 1 off situations that remove the standard options for gauging value. The situations I have in mind are IPOs and one-off strange happenings. The particular instances I have in mind are the Facebook IPO and the situations where the markets wake up in the AM to a so-called new world. Situations such as when something big has happened. Companies hit by natural disaster, countries governments disintegrating or wars starting etc. These result in sudden big changes in company fortunes that are reflected in stock markets.