Finkel (1985,1987),for instance finds that voting and working on a campaign have different effects on individual satisfaction with democracy, but many other studies have opted to collapse different types of political participation into a single index (e.g., Nadeau and Blais, 1993; Espinal, Hartlyn and Kelly, 2006), masking potentially important distinctions between these.
The simultaneity bias issue is again significant here.There is serious reason to believe that individuals dissatisfied with some part of their lives might be more likely to take certain types of political action (such as participating in a protest against a deleterious policy) as compared to individuals with otherwise similar observable characteristics. To the extent that life dissatisfaction goes undetected in a mass survey of the type we analyze here, we will be unable to "control" for it in statistical analysis. This again points to the fact that an experimental design might be necessary to truly identify the causal effect of political participation on life satisfaction.