Archive for the ‘Best Practices’ Category

« Older Entries

Google buys Metaweb: Can corporations acquire the halo effect of the underdog?

Monday, July 26th, 2010

Google recently bought Metaweb, a major semantic web company.  The value of Metaweb to Google is obvious — as ReadWriteWeb notes, “For the most part,…Google merely serves up links to Web pages; knowing more about what is behind those links could allow the search giant to provide better, more contextual results.” But what does the purchase mean for Metaweb?

Big companies buy small companies all the time.  Some entrepreneurs create their start-ups with that goal in mind — get something going and then make a killing when Google buys it.  But what do you think of a company when it seems to be doing something different and then is bought by Google?

Metaweb was never a nonprofit, but like Wikipedia, it has had a similar, community-driven vibe.  Freebase, its database of entities, is crowd-sourced, open, and free.  Google promises that Freebase will remain free, but will the community of people who contribute to Freebase feel the same contributing free labor to a mega-corporation?  Is there anything keeping Google from changing its mind in the future about keeping Freebase free?  How will the culture of Metaweb change as its technologies evolve within Google?

This isn’t to say that Metaweb’s goals have necessarily been compromised by its purchase by Google.   Many people feel like this is the best thing that could have happened to the semantic web.

(Though a few feel, “They didn’t make it big. In fact, this means they failed at their mission of better organizing the world’s information so that rich apps could be built around it. They never got to the APPS part. FAIL!”, and at least one person is concerned Google bought Freebase to kill it.)

But what did you think when Google bought the nonprofit Gapminder, of Hans Rosling’s famous TED talk?

Or when eBay bought a 25% stake in Craigslist?

Or outside the tech world, when Unilever bought Ben & Jerry’s?

Can a company or organization maintain any high-minded mission to be driven by principles other than profit when they’re bought by a major publicly held corporation?

This isn’t just an abstract question for us.  One of the biggest reasons why we chose to be a 501(c)(3) nonprofit organization is that we wanted to make sure no one running the Common Data Project would be tempted to sell its greatest asset, the data it hopes to bring together, for short-term profit.  As a nonprofit, CDP is not barred from making profits, but no profits can inure to the benefit of any private individual or shareholder.  Also as a nonprofit, should CDP dissolve, it cannot merely sell its assets to the highest bidder but must transfer them to another nonprofit organization with a similar mission.

We’re still working on understanding the legal distinctions between IRS-recognized tax-exempt organizations and for-profit businesses.  We were surprised when we first found out that Gapminder, a Swedish nonprofit, had been bought by Google.  Swedish nonprofit law may differ from U.S. nonprofit law.  But it appears Hans Rosling did not stand to make a dime.  Google only bought the software and the website, and whatever that was worth went to the organization itself.  So in a way, the experience of Gapminder supports the idea that being a nonprofit does make a difference in restricting the profit motives of individuals.  Alex Selkirk, as the founder and President of CDP, will never make a windfall through CDP.

The fact that CDP is not profit-driven, and will never be profit-driven makes a difference to us.  Does it make a difference to you?

Tags: , , , ,
Posted in Best Practices, Building the Datatrust | No Comments »

In the mix…new organizational structures, giant list of data brokers, governments sharing citizens’ financial data, and what IT security has to do with Lady Gaga

Friday, July 9th, 2010

1) More on new kinds of organizational structures for entities that want to form for philanthropic purposes but not fit into the IRS definition of a nonprofit.

2) CDT shone a spotlight on Spokeo, a data broker last week.  Who are other data brokers? Don’t be shocked, there are A LOT of them.  What they do, they mainly do out of the spotlight shone on companies like Facebook, but with very real effects.  In 2005, ChoicePoint sold data to identity thieves posing as a legitimate business.

3) The U.S. has come to an agreement with Europe on sharing finance data, which the U.S. argues is an essential tool of counterterrorism.  The article doesn’t say exactly how these investigations work, whether specific suspects are targeted or whether large amounts of financial data are combed for suspicious activity.  It does make me wonder, given how data crosses borders more easily than any other resource, how will Fourth Amendment protections in the U.S. (and similar protections in other countries) apply to these international data exchanges?  There is also this pithy quote:

Giving passengers a way to challenge the sharing of their personal data in United States courts is a key demand of privacy advocates in Europe — though it is not clear under what circumstances passengers would learn that their records were being misused or were inaccurate.

4) Don’t mean to focus so much on scary data stuff, but 41% of IT professionals admit to abusing privileges.  In a related vein, it turns out a disgruntled soldier accused of illegally downloading classified data managed to do it by disguising his CDs as Lady Gaga CDs.  Even better,

He was able to avoid detection not because he kept a poker face, they said, but apparently because he hummed and lip-synched to Lady Gaga songs to make it appear that he was using the classified computer’s CD player to listen to music.

The New York Times is definitely getting cheekier.

Tags: , , , , ,
Posted in Best Practices, Protecting Privacy in Meaningful Ways | No Comments »

Who has your data and how can the government get it?

Monday, June 28th, 2010

Who has your data? And how can the government get it?

The questions are more complicated than they might seem.

In the last month, we’ve seen Facebook criticized and scrutinized at every turn for the way they collect and share their users’ data.  Much of that criticism was deserved, but what was missing in that discussion were the companies that have your data without even your knowledge, let alone your consent.

The relationship between a user and Facebook is at least relatively straightforward.  The user knows his or her data has been placed in Facebook, and legislation could be updated relatively easily to protect his or her expectation of privacy in that data.

But what about the data consumer service companies share with third parties?

Pharmacies sell prescription data that includes you; cellphone-related businesses sell data that includes you.

So much of the data economy involves companies and businesses that don’t necessarily have you as a customer, and thus even less incentive to protect your interests.

What about data that’s supposedly de-identified or anonymized?  We know that such data can be combined with another dataset to re-identify people.  Could the government seek that kind of data and avoid getting even a subpoena?  Increasingly, the companies that have data about you aren’t even the companies you initially transacted with.  How will existing privacy laws, even proposed reforms by the Digital Due Process coalition, deal with this reality?

These are all questions that consume us at the Common Data Project for good reason.  As an organization dedicated to enabling the safe disclosure of personal information, we are committed to talking about privacy and anonymity in measurable ways, rather than with vague promises.

If you read a typical privacy policy, you’ll see language that goes something like this,

Google only shares personal information with other companies or individuals outside of Google in the following limited circumstances:…

We have a good faith belief that access, use, preservation or disclosure of such information is reasonably necessary to (a) satisfy any applicable law, regulation, legal process or enforceable governmental request

We think the datatrust needs to be do better than that. We want to know exactly what “enforceable government request” means.  We want to think creatively about what individual privacy rights mean when organizations are sharing information with each other. We’ve written up the aspects that seem most directly relevant to our project here, including 1) a quick overview of federal privacy law; 2) implications for data collectors today; and 3) implications for the datatrust.

We ultimately have more questions than answers.  But we definitely can’t assume we know everything there is to know.  Even at the Supreme Court, where the Justices seem to have some trouble understanding how pagers and text messages work, they understand that the world is changing quickly.  (See City of Ontario v. Quon.)  We all need to be asking questions together.

So take a look.  Let us know if there are issues we’re missing. What are some other questions we should be asking?

Tags: , , , ,
Posted in Best Practices, Protecting Privacy in Meaningful Ways | No Comments »

In the mix…data for coupons, information literacy, most-visited sites

Friday, June 4th, 2010

1) There’s obviously an increasing move to a model of data collection in which the company says, “give us your data and get something in return,” a quid pro quo.  But as Marc Rotenberg at EPIC points out,

The big problem is that these business models are not very stable. Companies set out privacy policies, consumers disclose data, and then the action begins…The business model changes. The companies simply want the data, and the consumer benefit disappears.

It’s not enough to start with compensating consumers for their data.  The persistent, shareable nature of data makes it very different from a transaction involving money, where someone can buy, walk away, and never interact with the company again.  These data-centered companies are creating a network of users whose data are continually used in the business.  Maybe it’s time for a new model of business, where governance plans incorporate ways for users to be involved in decisions about their data.

2) In a related vein, danah boyd argues that transparency should not be an end in itself, and that information literacy needs to developed in conjunction with information access.  A similar argument can be made about the concept of privacy.  In “real life” (i.e., offline life), no one aims for total privacy.  Everyday, we make decisions about what we want to share with whom.  Online, total privacy and “anonymization” are also impossible, no matter the company promises in its privacy policy.  For our datatrust, we’re going to use PINQ, a technology using differential privacy, that acknowledges privacy is not binary, but something one spends.  So perhaps we’ll need to work on privacy and data literacy as well?

3) Google recently released a list of the most visited sites on the Internet. Two questions jump out: a) Where is Google on this list? and b) Could the list be a proxy for the biggest data collectors online?

Tags: , , , , , ,
Posted in Best Practices, Interesting Uses of Data, Protecting Privacy in Meaningful Ways | No Comments »

Mark Zuckerberg: It takes a village to build trust.

Friday, June 4th, 2010

This whole brouhaha over Facebook privacy appears to be stuck revolving around Mark Zuckerberg.

We seem to be stuck in a personal tug-of-war with the CEO of Facebook frustrated that a 26 year-old personally has so much power over so many.

Meanwhile, Mark Z. is personally reassuring us that we can trust Facebook which on some level implies we must trust him.

But should any single individual really be entrusted with so much? Especially “a 26 year-old nervous, sweaty guy who dodges the questions.” Harsh, but not a completely invalid point.

As users of Facebook, we all know that it is the content of all our lives and our relationships to each other that make Facebook special. As a result, we feel a sense of entitlement about Facebook policy-making that we don’t feel about services that are in many ways way more intrusive and/or less disciplined about protecting privacy (e.g. ISPs, cellphone providers, search).

Another way of putting it is, Facebook is not Apple! and as a result, needs a CEO who is a community leader, not a dictator of cool.

So we start asking questions like, why should Facebook make the big bucks at the expense of my privacy? Shouldn’t I get a piece of that?

(Google’s been doing this for over a decade now, but the privacy exposure over at Google is invisible to the end-user.)

At some point, will we decide we would rather pay for a service than feel like we’re being manipulated by companies who know more about us than we do and can decide whether to use that information to help us or hurt us depending on profit margin. Here’s another example.

Or are there other ways to counterbalance the corporate monopoly on personal information? We think so.

In order for us to trust Facebook, Facebook needs to stop feeling like a benevolent dictatorship, albeit one open to feedback, but also one with a dictator who looks like he’s in need of a regent.

Instead Facebook the company should consider adopting some significant community-driven governance reforms that will at least give it the patina of a democracy.

(Even if at the end of the day, it is beholden to its owners and investors.

For some context, this was the sum total of what Mark Z. had to say about how important decisions are made at Facebook:

We’re a company where there’s a lot of open dialogue. We have crazy dialogue and arguments. Every Friday, I have an open Q&A where people can come and ask me whatever questions they want. We try to do what we think is right, but we also listen to feedback and use it to improve. And we look at data about how people are using the site. In response to the most recent changes we made, we innovated, we did what we thought was right about the defaults, and then we listened to the feedback and then we holed up for two weeks to crank out a new privacy system.

Nothing outrageous. About par for your average web service. (But then again, Facebook isn’t your average web service.)

However, this is what should have been the meat of the discussion about how Facebook is going to address privacy concerns: community agency and decision-making, not Mark Z.’s personal vision of an interwebs brimming with serendipitous happenings.

Facebook the organization needs to be trusted. So it might be best if Mark Z. backed out of the limelight and stopped being the lone face of Facebook.

How might have that D8 interview have turned out if he had come on stage with a small group of Facebook users?

What governance changes would make you feel more empowered as a Facebook user?

Tags: , ,
Posted in Best Practices, Protecting Privacy in Meaningful Ways | No Comments »

Governing the Datatrust: Answering the question, “Why should I trust you with my data?”

Thursday, June 3rd, 2010

Progress on defining the datatrust is accelerating–we can almost smell it!

For a refresher, the datatrust is an online service that will allow organizations to open sensitive data to the public and provide researchers, policymakers and application developers with a way to directly query the data, all without compromising individual privacy. Read more.

For the past two years, we’ve been working on figuring out exactly what the datatrust will be, not just in technical terms, but also in policy terms.

We’ve been thinking through what promises the datatrust will make, how those promises will be enforced, and how best we can build a datatrust that is governed, not by the whim of a dictator, but by a healthy synergy between the user community, the staff, and the board.

The policies we’re writing and the infrastructure we’re building are still a work in progress.  But for an overview of the decisions we’ve made and outstanding issues, take a look at “Datatrust Governance and Policies: Questions, Concerns, and Bright Ideas”.

Here’s a short summary of our overall strategy.

  1. Make a clear and enforceable promise around privacy.
  2. Keep the datatrust simple. We will never be all things to all people. The functions it does have will be small enough to be managed and monitored easily by a small staff, the user community, and the board.
  3. Have many decision-makers. It’s more important that we do the right thing than that we do them quickly. We will create a system of checks and balances, in which authority to maintain and monitor the datatrust will be entrusted to several, separate parties, including the staff, the user community, and the board.
  4. Monitor, report and review, regularly. We will regularly review what we’re monitoring and how we’re doing it. Release results to the public.
  5. Provide an escape valve. Develop explicit, enforceable policies on what the datatrust can and can’t do with the data. Prepare a “living will” to safely dispose of the data if the organization can no longer meet its obligations to its user community and the general public.

We definitely have a lot of work to do, but it’s exciting to be narrowing down the issues.  We’d love to hear what you think!

P.S. You can read more about the technical progress we’re making on the datatrust by visiting our Projects page.

Tags:
Posted in Best Practices, Building the Datatrust, CDP Announcements | No Comments »

Measuring the privacy cost of “free” services.

Wednesday, June 2nd, 2010

There was an interesting pair of pieces on this Sunday’s “On The Media.”

The first was “The Cost of Privacy,” a discussion of Facebook’s new privacy settings, which presumably makes it easier for users to clamp down on what’s shared.

A few points that resonated with us:

  1. Privacy is a commodity we all trade for things we want (e.g. celebrity, discounts, free online services).
  2. Going down the path of having us all set privacy controls everywhere we go on internet is impractical and unsustainable.
  3. If no one is willing to share their data, most of the services we love to get for free would disappear. Randall Rothenberg.
  4. The services collecting and using data don’t really care about you the individual, they only care about trends and aggregates. Dr. Paul H. Rubin.

We wish one of the interviewees had gone even farther to make the point that since we all make decisions every day to trade a little bit of privacy in exchange for services, privacy policies really need to be built around notions of buying and paying where what you “buy” are services and how you pay for them are with “units” of privacy risk (as in risk of exposure).

  1. Here’s what you get in exchange for letting us collect data about you.”
  2. Here’s the privacy cost of what you’re getting (in meaningful and quantifiable terms).

(And no, we don’t believe that deleting data after 6 months and/or listing out all the ways your data will be used is an acceptable proxy for calculating “privacy cost.” Besides, such policies inevitably severely limit the utility of data and stifle innovation to boot.)

Gaining clarity around privacy cost is exactly where we’re headed with the datatrust. What’s going to make our privacy policy stand out is not that our privacy “guarantee” will be 100% ironclad.

We can’t guarantee total anonymity. No one can. Instead, what we’re offering is an actual way to “quantify” privacy risk so that we can track and measure the cost of each use of your data and we can “guarantee” that we will never use more than the amount you agreed to.

This in turn is what will allow us to make some measurable guarantees around the “maximum amount of privacy risk” you will be exposed to by having your data in the datatrust.

The second segment on privacy rights and issues of due process vis-a-vis the government and data-mining.

Kevin Bankston from EFF gave a good run-down how ECPA is laughably ill-equipped to protect individuals using modern-day online services from unprincipled government intrusions.

One point that wasn’t made was that unlike search and seizure of physical property, the privacy impact of data-mining is easily several orders of magnitude greater. Like most things in the digital realm, it’s incredibly easy to sift through hundreds of thousands of user accounts whereas it would be impossibly onerous to search 100,000 homes or read 100,000 paper files.

This is why we disagree with the idea that we should apply old standards created for a physical world to the new realities of the digital one.

Instead, we need to look at actual harm and define new standards around limiting the privacy impact of investigative data-mining.

Again, this would require a quantitative approach to measuring privacy risk.

(Just to be clear, I’m not suggesting that we limit the size of the datasets being mined, that would defeat the purpose of data-mining. Rather, I’m talking about process guidelines for how to go about doing low-(privacy) impact data-mining. More to come on this topic.)

Tags: , , , , , ,
Posted in Best Practices, Protecting Privacy in Meaningful Ways, Public Policy, The Future of Advertising and Media | No Comments »

Ten Things We Learned About Communities

Tuesday, June 1st, 2010

After 8 posts and several thousand words on how communities encourage participation, define membership, sustain networks, and govern themselves, what have we learned?

Dimitri Damasceno Creative Commons Attribution ShareAlike 2.0 (Generic)

We started this study because the datatrust we are working to build will depend on an invested and active community.  We want data donors, data borrowers, and data curators to interact as members of a community that are empowered to manage data, monitor the community, and hold the datatrust accountable to its mission.

So here are the findings we think are most relevant to the datatrust:

What motivates high-quality participation?

1. People are motivated to participate by rewards, but also by a desire to enhance their reputations.

Do communities need to have a mission?

2.  A shared ethos, culture, or mission are important if you want members of the community to be invested in the community and its survival as an institution.

3.  A shared ethos, culture, or mission also make it harder to have a very large and diverse community of people with different tastes and goals.

Should we require real identities?

4. People care more about their reputations when their real identities are on the line.

Can a community get too big?

5. If a large social network is to maintain a sense of small-scale community, it needs to reinforce a feeling of smaller communities within the social network.

Does diversity matter, in what way and why?

6. Diversity isn’t necessary for a successful community, but it’s important if the community’s goals require participation from a broad and diverse range of people.

Should you have to “pay to play”?

7.  We have always anticipated instituting a clear quid pro quo in the datatrust community – if you donate data, you get access to data.  Although we value the clarity of that exchange, will it limit our ability to grow?

Do more privacy controls=more control over privacy?

8.  People need to understand intuitively where information is going and to whom for privacy controls to be meaningful.

Is self-governance worth it?

9.  Decentralization of power and transparency can go a long way in helping an organization build trust.

10.  But you will have to put up with people who argue about what color to paint the bike shed.

Tags:
Posted in Best Practices, Building the Datatrust | No Comments »

Building a community: who’s in charge?

Friday, May 28th, 2010

From http://xkcd.com/

We’ve seen so far that for a community to be vibrant and healthy, people have to care about the community and the roles they play in it.  A community doesn’t have to be a simple democracy, one member/one vote on all decisions, but members have to feel some sense of agency and power over what happens in the community.

Of course, agency can mean a lot of things.

On one end of the spectrum are membership-based cooperatives, like credit unions and the Park Slope Food Coop, where members, whether or not they exercise it, have decision-making power built into the infrastructure of the organization.

On the other end are most online communities, like Yelp, Facebook, and MySpace.  Because the communities are all about user-generated content, users clearly have a lot of say in how the community develops.

But generally speaking, users of for-profit online services, even ones that revolve around user-generated content don’t have power to actually govern the community or shape policies.

Yelp, for example, allows more or less anyone to write a review.  But the power to monitor and remove reviews for being shills, rants or otherwise violations of its terms of use is centralized in Yelp’s management and staff.  The editing is done behind closed doors, rather than out in the open with community input.  Given its profit model, it’s not surprising that Yelp has been accused repeatedly of using its editing power as a form of extortion when it tries to sell ads to business owners.

Even if Yelp is innocent, it doesn’t help that the process is not transparent, which is why Yelp has responded by at least revealing which reviews have been removed.

(As for Facebook, the hostility between the company and at least some of its users is obvious.  No need to go there again.)

And then there are communities that are somewhere in between, like Wikipedia.  Wikipedia isn’t a member-based organization in a traditional sense.  Community members elect three, not all, of the board members of Wikimedia.  Each community member does not have the same amount of power as another community member – people who gain greater responsibilities and greater status also have more power.  But many who are actively involved in how Wikipedia is run are volunteers, rather than paid staff, who initially got involved the same way everybody does, as writers and editors of entries.

There are some obvious benefits to a community that largely governs itself.

It’s another way for the community to feel that it belongs to its members, not some outside management structure.  The staff that runs Wikipedia can remain relatively small, because many volunteers are out there reading, editing, and monitoring the site.

Perhaps most importantly, power is decentralized and decisions are by necessity transparent.  Although not all Wikipedia users have access to all pages, there’s an ethos of openness and collaboration.

For example, a controversy recently erupted at Wikipedia.  Wikimedia Commons was accused of holding child pornography.  Jimmy Wales, the founder of Wikipedia, then started deleting images.  A debate ensued within the Wikipedia community about whether this was appropriate, a debate any of us can read.  Ultimately, it was decided that he would no longer have “founder” editing privileges, which had allowed him to delete content without the consent of other editors.  Wikimedia also claims that he never had final editorial control to begin with.  Whether or not Wikimedia is successful, it wants and needs to project a culture of collaboration, rather than personality-driven dictatorship.

It’s hard to imagine Mark Zuckerberg giving up comparable privileges to resolve the current privacy brouhaha at Facebook.

But it’s not all puppies and roses, as anyone who’s actually been a part of such a community knows.

It’s harder to control problems, which is why a blatantly inaccurate entry on Wikipedia once sat around for 123 days.  Some community members tend to get a little too excited telling other members they’re wrong, which can be a problem in any organization, but is multiplied when everyone has the right to monitor.

Some are great at pointing out problems but not so good at taking responsibility for fixing them.

And groups of people together can rathole on insignificant issues (especially on mailing lists), stalling progress because they can’t bring themselves to resolve “What color should we paint the bikeshed?” issues.

Wikipedia has struggled with these challenges over the past ten years.  It now limits access to certain entries in order to control accuracy, but arguably at some cost to the vibrancy of the community.  Wikipedia is trying to open up Wikipedia in new directions, as it tries a redesign in the hope it will encourage more diverse groups to write and edit entries (though personally, it looks a lot like the old one).

Ultimately, someone still has to be in charge.  And when you value democracy over dictatorship, it’s harder but arguably more interesting, to figure out what that looks like.

Tags: , , , , ,
Posted in Best Practices | No Comments »

Recap and Proposal: 95/5, The Statistically Insignificant Privacy Guarantee

Wednesday, May 26th, 2010


Image from: From MATLAB fuzzy logic toolbox documentation.

In our search for a privacy guarantee that is both measurable and meaningful to the general public, we’ve traveled a long way in and out of the nuances of PINQ and differential privacy: A relatively new, quantitative approach to protecting privacy. Here’s a short summary of where we’ve been followed by a proposal built around the notion of statistical significance for where we might want to go.

The “Differential Privacy” Privacy Guarantee

Differential privacy guarantees that no matter what questions are asked and how answers to those questions are crossed with outside data, your individual record will remain “almost indiscernible” in a data set protected by differential privacy. (The corollary to that is that the impact of your individual record on the answers given out by differential privacy will be “negligeable.”)

For a “quantitative” approach to protecting privacy, the differential privacy guarantee is remarkably NOT quantitative.

So I began by proposing the idea that the probability of a single record being present in a data set should equal the probability of that single record not being present in that data set (50/50).

I introduced the idea of worst-case scenario where a nosy neighbor asks a pointed question that essentially reduces to a “Yes or no? Is my neighbor in this data set?” sort of question and I proposed that the nosy neighbor should get an equivocal (50/50) answer: “Maybe yes, but then again, (equally) maybe no.”

(In other words, “almost indiscernible” is hard to quantify. But completely indiscernible is easy to quantify.)

We took this 50/50 definition and tried to bring it to bear on the reality of how differential privacy applies noise to “real answers” to produce identity-obfuscating “noisy aswers.”

I quickly discovered that no matter what, differential privacy’s noisy answers always imply that one answer is more likely than another.

My latest post was a last gasp explaining why there really is no way to deliver on the completely invisible, completely non-discernible 50/50 privacy guarantee (even if we abandoned Laplace).

(But I haven’t given up on quantifying the privacy guarantee.)

Now we’re looking at statistical significance as a way to draw a quantitative boundary around a differential privacy guarantee.

Below is a proposal that we’re looking for feedback on. We’re also curious to know if anyone else tried to come up with a way to quantify the differential privacy guarantee?

What is Statistical Significance? Is it appropriate for our privacy guarantee?

In statistics, a result is called statistically significant if it is unlikely to have occurred by chance. Applied to our privacy guarantee, you might ask the question this way: When you get an answer about a protected data set, are the implications of that “differentially private” answer (as in implications about what the “real answer” might be) significant or are they simply the product of chance?

Is this an appropriate way to define a quantifiable privacy guarantee, we’re not sure.

Thought Experiment: Tossing a Weighted Coin

You have a coin. You know that one side is heavier than the other side. You have only 1 chance to spin the coin and draw a conclusion about which side is heavier.

At what weight distribution split does the result of that 1 coin spin start to be statistically significant?

Well, if you take the “conventional” definition of statistical significance where results start to be statistically significant when you have less than a 5% chance of being wrong, the boundary in our weighted coin example would be 95/5 where 95% of the weight is on one side of the coin and 5% is on the other.

What does this have to do with differential privacy?

Mapped onto differential privacy, the weight distribution split is the moral equivalent of the probability split between two possible “real answers.”

The 1 coin toss is the moral equivalent of being able to ask 1 question of the data set.

With a sample size of 1 question, the probability split between two possible, adjacent “real answers” would need to be at least 95/5 before the result of that 1 question was statistically significant.

That in turn means that at 95/5, the presence or absence of a single individual’s record in a data set won’t have a statistically significant impact on the noisy answer given out through differential privacy.

(Still 95% certainty doesn’t sound very good.)

Postscript Obviously, we don’t want to be a situation where asking just 1 question of a data set brings it to the brink of violating the privacy guarantee. However, thinking in terms of 1 question is helpful way to figure out the “total” amount of privacy risk the system can tolerate. And since the whole point of differential privacy is that it offers a quantitative way to track privacy risk, we can take that “total” amount and divide it by the number of questions we want to be able to dole out per data set and arrive at a per-question risk threshold.

Tags: , ,
Posted in Best Practices, Protecting Privacy in Meaningful Ways | No Comments »

« Older Entries
Get Adobe Flash playerPlugin by wpburn.com wordpress themes