>Is there any evidence to show that signing a petition makes a person more inclined to take additional practical action?
Yes, there is some evidence. In Chapter 3 of Influence: Science and Practice, Robert Cialdini discusses this kind of self-image effect, citing several studies including one in particular about petitions[1]. These kinds of "commitments" (even though they are not actually binding) really do affect our behavior, although the end results are not necessarily particularly issue-focused or predictable.
One thing we can say though with some certainty: if you convince someone to sign their name to a petition that says "stop X", it will take significant mental effort for them to later decide that they actually support X.
Remember, these were innocuous requests from a non-profit group with relatively non-controversial goals. This technique may not produce the same results for more political or more controversial requests.
Yes, there is some evidence. In Chapter 3 of Influence: Science and Practice, Robert Cialdini discusses this kind of self-image effect, citing several studies including one in particular about petitions[1]. These kinds of "commitments" (even though they are not actually binding) really do affect our behavior, although the end results are not necessarily particularly issue-focused or predictable.
One thing we can say though with some certainty: if you convince someone to sign their name to a petition that says "stop X", it will take significant mental effort for them to later decide that they actually support X.
[1] http://psycnet.apa.org/journals/psp/4/2/195/