Are online petitions effective?

Websites like GetUp and Change.org claim that online petitions can force governments and large corporations to change policies, but is this really true?

Claimed petition victories
Change.org claims responsibility for victories including:
1. Legalising adoption for same sex couples in South Australia
2. Convincing Allianz Insurance to pay out an insurance claim for a man hit by a car
3. Saving the Brunswick Heads picture house from being shut down

GetUp claims responsibility for victories including:
1. A 2010 high court case powered by petitions and crowdfunding that changed electoral laws so that people could enrol to vote after the election was declared allowing an additional 98 138 people to vote.
2. Causing major swings in the 2016 federal election against hardline federal candidates (e.g. Andrew Nikolic).
3. Helping to ensure (some) asylum seekers were allowed to stay in Australia rather than being detained in Nauru.

Were these victories really a result of petitions?
The cynical among us would turn up their noses at these claims - how much can a petition actually achieve on its own? After all, there is no mandated process for the Australian parliament to discuss or debate petitions (unlike the US or UK where the government must officially respond to petitions that reach a critical threshold). What's more, there is almost always broadcast media involvement to amplify the voice of the petitioners. Change doesn't happen in a vacuum so to say petitions are solely responsible for any of these developments is probably incorrect.

So they probably help and can't hurt, right?
I've always approached petitions from the attitude that they are probably not super effective on their own but the cost is minimal and the potential upside is very high. If they don't hurt very much (max a minute of your time to sign a petition) and can help, why wouldn't you do it? It's a bit like Pascal's gambit.

Downsides of petitions
There is some evidence that petitions can actually be harmful. A study by Schumann and Klein (2015) found that people who signed petitions were less likely to subsequently take offline action (e.g. attending a rally). This is a fairly alarming result for petition pushers but it's worth noting that the study is not tremendously rigorous in my opinion. The study from which the authors drew the conclusion that offline participation is less likely after signing petitions only had 76 participants. What's more the petition was designed by the researchers and the participants were university students receiving class credit for participation. As such, it probably does not represent the way people interact with real petitions. It's certainly food for thought but it would need to be followed by solid empirical research on petitions out in the wild.

Reality check - petitions are not enough (and campaigners know that)
I don't think many people would argue that petitions are enough on their own. Pretty much every online petition site encourages petition creators to ask people who sign to do more. Change.org, for example, has a "Tactics Bank" where tactics are divided into "Low commitment, low impact activities " (e.g. sharing a video on Facebook), "Higher commitment, higher impact activities" (e.g. making a donation, calling an MP), and "Highest commitment, highest impact activities" (e.g. attending an in person protest outside an MP's office).

The benefit of platforms like Change.org and GetUp.org is that their campaigners are aware of the tendency towards low impact engagement and try to drive people to higher levels of commitment. If you want to make change, these platforms are a good way to synchronise efforts. One person is easy to ignore but one thousand people acting in concordance is hard to miss.

I'm not likely to hear about a rally if I don't sign up with one of these campaigns. From my perspective, a petition is simply a way of saying "I care about this issue and am open to taking action to try to change it".

Choosing which issues to engage with
Time and energy is finite. I sign a lot of petitions but am not committed to taking action for most of them. For example, the Greens organised a march across the Sydney Harbour Bridge today in solidarity with Indigenous Australians that happened this afternoon. I was vaguely hoping to attend but had also committed to volunteer with the SES today and couldn't make it work. As such, I'm essentially a Slacktivist in this cause. I've signed a few petitions around Indigenous rights but haven't done much more.

I suspect that's probably the reality for most people. Does that mean that signing the petitions was worthless? Is the only meaningful impact to be found by marching on the streets? I don't think it works that way. Any social movement is likely to resemble a pyramid where there is an inverse correlation between level of commitment and number of people at that level of commitment.

Only a few people will devote their lives to a cause. More of them will be willing to attend community meetings, create banners and attend protests. Even more will be willing to chuck in a few dollars and write a letter or two. Most people will engage at a tokenistic level.

But the point is that the movement needs all these levels. If done well, the campaign will energise people to move up the ladder of commitment. Someone who signs a petition might well become the next marcher. But it's rare for someone to go from 0-100. Just like the way "overnight successes" are normally several years in the making, an effective campaign organiser is likely to have contributed in a smaller way in other campaigns.

The sheer number of signatures on a petition does have some impact. If 5000 people sign a petition on a national issue, chances are no-one in power will pay attention. But if 500,000 people do, you can bet there will be some discussion.

TL;DR
Petitions are useless on their own. However, in a well designed campaign, petitions link people to other supporters and empower people to up their commitment and contribute to deeply impactful programs of change. If I think/say I care about an issue but am not willing to sign a petition, I'd better be already taking action at a higher level or else I'm lying to yourself and others. I can't contribute to everything but I can pick one or two issues (climate change for me) to focus intently on and do a little to help with the rest.