Abstract: We investigate the relative importance of diffusion and jumps in a new jump diffusion model for asset returns. in contrast to the standard modeling of jumps for asset returns. The jump component of our process can display finite or infinite activity, and finite or infinite variation. Empirical investigations of time series indicates that index dynamics are essentially devoid of a diffusion component, while this component may be present in the dynamics of individual stocks. This result leads to the conjecture that the risk-neutral process should be free of a diffusion component for both indices and individual stocks. Empirical investigation of options data tends to confirm this conjecture. We conclude that the statistical and risk-neutral processes for indices and stocks tend to be pure jump processes of infinite activity and finite variation.

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