Introduction

We conduct an extensive empirical study comparing the relative riskiness of two UK equity markets run by the London Stock Exchange: AIM the market for growth companies versus the Main Market, the market for more established companies. AIM has been a considerable success. Even by its survival over 19 years it has succeeded in relation to similar markets in other countries. During that period it has seen rapid growth and has emerged as the market of choice for smaller, newer companies in the UK and increasingly elsewhere. Investors often perceive AIM as riskier than the Main Market for comparable stocks. At a superficial level we find that AIM stocks may seem more risky than comparable Main Market stocks, but as the analysis is refined to ensure that the comparisons focus purely on the effect of being on different markets the difference shrinks and finally disappears. This conclusion concurs with the market practitioner’s view that there is no significant risk differential.