Why Do You Lie? The Perils of Self-Reporting

I am always surprised at how easily, and cheaply, we humans lie.

Have you ever been in a conversation about, say, a particular book and been tempted to say you’ve read it even though you haven’t?

I am guessing the answer is yes. But why would anyone bother to lie in such a low-stakes situation?

The book lie is what you might call a lie of reputation: you are concerned with what other people think of you. Of the many reasons that people lie, I have always thought that the lie of reputation is the most interesting — as opposed to a lie to gain advantage, to avoid trouble, to get out of an obligation, etc.

A new paper by the economists Cesar Martinelli and Susan W. Parker offers some fascinating insights into lies of reputation. It is called “Deception and Misreporting in a Social Program,” and will be published soon in the Journal of the European Economics Association.

Martinelli is a Peruvian-born, U.C.L.A.-educated economic theorist who teaches at I.T.A.M. in Mexico City; Parker is an American-born economist, educated at Yale, who also teaches in Mexico City, at C.I.D.E..

Their paper takes advantage of a remarkably rich data set from Oportunidades, a Mexican welfare program. It records the household goods that people say they have when they are applying for the program and then it also records the household goods that are actually found to be in that household once the recipient’s application has been accepted. Martinelli and Parker worked with data from more than 100,000 applicants, representing 10 percent of the applicants interviewed that year (2002).

It turned out that a lot of people underreported certain items that they thought might exclude them from getting benefits. Below is a list of underreported items followed by the percentage of recipients who owned a certain good but who said they didn’t:

Car (83.10 percent)
Truck (81.71)
Video recorder (79.73)
Satellite TV (73.91)
Gas boiler (73.12)
Phone (73.12)
Washing machine (53.46)

That’s not very surprising: you might expect people to lie to gain the advantage of a welfare benefit. But here’s the surprise. Below is a list of household items that were overreported — i.e., which applicants said they had but in fact did not (again, followed by percentages):

Toilet (39.07 percent)
Tap water (31.76)
Gas stove (28.56)
Concrete floor (25.41)
Refrigerator (12.05)

So 4 out of 10 applicants without a toilet said they had one. Why?

Martinelli and Parker chalk it up to embarrassment, plain and simple. People who were desperately poor were also apparently desperate to not admit to a welfare clerk that they lived without a toilet or running water or even a concrete floor. This is one of the most amazing lies of reputation I can imagine.

It should be noted that there is a lot of incentive to lie to get into the Oportunidades program, for the cash benefit equals about 25 percent of the average applicant household’s expenditures. Furthermore, the penalty for underreporting was not very strong: many of the people found to be underreporting goods like satellite TV’s and trucks were were not kicked out of the program. You could argue that the penalty for overreporting, meanwhile, was greater since it might mean being excluded from the program in the first place — which makes the overreporting even more costly.

The Martinelli-Parker paper may have broad implications for not only poverty programs but any kind of project where the data are self-reported. Think about the typical survey on drug use, sexual behavior, personal hygiene, voting preference, environmental behavior, etc.

Here’s what we once wrote, for instance, in an article about the lack of hand hygiene in hospitals:

In one Australian medical study, doctors self-reported their hand-washing rate at 73 percent, whereas when these same doctors were observed, their actual rate was a paltry 9 percent.

We’ve also written about the subjects that online daters are most likely to lie about, and the risky business of election polling — especially when the issue of race is involved.

But as often as we or anyone else writes about the perils of self-reporting, the Martinelli-Parker paper really gives the whole topic a foundation to stand on. Not only does it deliver a surprising insight into why we lie, but it is also a sobering reminder to naturally distrust self-reported data — at least until some scientists enable us to peer into one another’s minds and see what’s really going on there.

I am interested in hearing from readers what kinds of lies you tell, and why.

[Note: I’ll be discussing this topic early tomorrow (Tues.) morning on the new public-radio program The Takeaway.]


What about silent lies? For years, my friends would talk about Star Wars, and I would just never speak during these conversations because it was embarrassing to admit I hadn't seen the movies (we're all such nerds). Thus they assumed since I hadn't stated that I hadn't, I had seen them. Is this as much of a lie as telling them outright that yes, I saw the movies?

Re: #16: My height and weight on my driver's license were true when I got it... I hope you won't consider it a lie now, as I'll freely admit I've gained both height and weight. That's just a past truth.


With regards to 26 and others, I believe the way the statistics should be interpreted is that "of the respondents who reported having X item (or NOT having X item) Y% were lying".

They are not percentages of everyone who responded because then you would be right, and there's no way those numbers make sense.

This is a good example of bad writing about statistics (no offense) it can be very difficulty to concisely state the exact premise of a statistic, although to be technically correct, these are parameters, not statistics.


In my work I regularly do 'health assessments' with clients. During these brief interviews it's fairly obvious when someone, for whatever reason, is lying. As if by saying they are well makes them so. Usually I know they are lying when the same question asked later in another way is inconsistent. Perhaps I'm seen as an authority and they routinely lie to authority. But it's for their own benefit this assessment and proving to me they are fine when they are not will one day catch up with them. They didn't want help from me, but then why, why even show up for an assessment?? I guess what I've learned is people are more complex than I ever knew possible.

Matt Weber

Maybe the people who "overreport" toilets and running water are lying, not because they're ashamed, but because they think the readers won't believe they lack such basic amenities...


My favorite lie:
When someone, who I have apparently developed an immediate prejudice against, asks me directions. I respond with "I'm sorry I don't speak English" without making up any funny accent to make it believable.

When I was briefly working in Poland I had memorized something to say, and tried to say it in as unaccented Polish as possible, for the same situation. It went something like this:

I'm sorry but I don't speak a single word of Polish, you might want to find somebody who does.

Funny, that when a fellow passenger on the MTA sought me out and approached me directly in Polish, I chose to struggle through an attempt to help.

A funny experiment that has a connection to this is trying to guess the accent of the person asking for directions and then launching into whatever language you think is their mother tongue. Guessing either right or wrong has pretty interesting results.

On top of this, I feel a tiny bit of an insult when I try to speak Japanese and the locals respond in English. I feel a lot more of an insult when it happens in a European context.

In regards to lies in the service of wooing the opposite sex. I memorized a sentence in Latvian that went:

I am so fertile that just kissing my big toe will bring you twins.

It wasn't a very successful strategy.



I try to hide the pain inside,
I want to confide
But find I've lied.


Self-reported health status is an area that can be a little shaky. Some research suggests (although can't prove) that perhaps one of the reasons for lower labour force participation among people with mild to moderate illness/disability is not due to inability to do the work, discrimination etc. but that those without jobs use their disability to justify their lack of employment.


"I like a look of agony,
Because I know its true."

~Emily Dickinson

michael b

College Students -

In a roundabout way, many college students lie about their "income" (though many college students have none and may well be receiving financial aid from their parents) by over-tipping.

Throwing a few extra dollars down on the bar after ordering a round makes you look like a big-shot.

Its a bit like leasing an expensive car but barely being able to fill its tank with gas - a line used in hip hop lyrics ("got a 1/4 tank of gas in my new E-Class, but that's alright 'cuz I stay fly")


There is a Calvin & Hobbes strip where Calvin spews outrageous lies in a reader survey for the "Chewing" magazine. He explains himself by saying "I love messing with data."

Here is a link to the strip: http://www.s-anand.net/calvinandhobbes.html#19950823

Dan Wylie-Sears

I don't see the point in technically "not lying" when deceiving people. It's still lying, in any way that matters.


# 124

It is funny you are posting to a column about lying when you are either lying about your name or if you are E. Zedillo you had a lot of "tranzar para avanzar" to do to become a President. Just an observation.

Dylan Thurston

I'm distressed that two previous commenters and Prof. Dubner seem to have failed to read the article to see what the "39.07%" overreporting rate actually means. If you look at Table I on page 6 of the linked PDF, it clearly states that they mean of the 26.92% of applicant households without a toilet, 39.07% lied and said they did have one. For those keeping score, that's 10.51% of all applicants falsely claiming to have a toilet, compared to the 12.11% of all applicants falsely claiming not to have a toilet. From what I gather from previous comments, the original formulation in the article was "So 4 out of 10 applicants who didn't have a toilet said they did", which seems like a fair summary, but has since been incorrected.

Chris S.

I used to live in a poorer neighborhood (eastern NC) where we often had solicitors trying to get us to go to one of the local churches. I told the first couple that I was an atheist (true) which resulted in a full throttle conversion effort that was difficult to end politely.

After that, I began telling church solicitors that I was Jewish. (Eastern NC, remember?) This response always resulted in a stunned pause followed by "Sorry to disturb you" and a hasty exit. I still use this lie to this day.


I find one class of (apparent) lies: intriguing: the number of sexual partners one has had. Heterosexual women report far fewer partners than heterosexual men do. In reality, it is mathematically impossible for this to be the case, since on average both genders must have the same number of partners. Of course, maybe this phenomenon is not based on lying but on a significantly different standard deviation for men and women; I doubt it, however.


I agree with #99. Telling people the truth about myself (books, activities, etc.) makes a conversation more interesting...it wastes less time getting to the interesting stuff.

I'm annoyed when I hear a friend tell a "white lie" about why they did something...I just won't say anything.


Personally, I lie very rarely and only in extreme circumstances. Say 2 or 3 times per year.

I'm not sure if white lies are immoral or unethical per se, but what I do think is that they reflect cowardice and lack of character in most circumstances. If you lie to spare someone's feelings or get out of a conversation, you are not demonstrating the fortitude and integrity to tell them the unpleasant truth to their face.

White lies also have the practical disadvantage that, if you are caught, and if you are lying over and over again to the same people you WILL get caught, your reputation will suffer greatly and you will be branded a liar. Losing people's respect will harm you much in the long run.

Another downside of lying is that you have to keep track of your lies. If you later tell the person that you lied to a statement that is inconsistent with you previous lie, you will, again, get caught, and your reputation will suffer greatly.

In sum, to avoid all this cognitive drain, and also because I consider myself a person of strength, honor and integrity, I only lie when it is absolutely necessary and unavoidable.



For those of you who lie about the books you've read or movies you've seen, don't you worry about being found out? If people mention a book or bring it up, they are likely to then start asking you about specifics of it. I never lie about this sort of thing because I'm not bold enough. I don't get how people do. I'd actually like an explanation. My question isn't rhetorical.

To #12 don't you still worry about being found out? Then you have to continue to say you are a vegetarian around this person, and what if someone else you know comes around and outs your lie, or what if you forget? It sounds risky to me....


Lie? Bwahahaha!

"Actually, dear, your butt does look fat. And I don't particularly like those jeans. I would really rather you wear a skirt and get out to the gym more, but I'm willing to overlook that because we've got a lot of history together I'm not willing to throw away."

Duh, of course we lie.

It's not good to go too far down that road (for anyone) but a lot of untruths are better for the parties concerned. Many questions aren't asked with the expectation of a truthful answer either.

Someone else noted explaining what you do for a living to people who don't understand. Ditto for me, though that tends to happen when people ask about my research (am an academic). I often say "You probably don't want to know. You might think you do, but it'll take an hour to explain it."


I lie about being late. I probably lie about how much I eat.

I used to lie to doctors about how much I drank, ate, exercised, etc. I realized that was self destructive. Now I rigorously try to tell them the truth. It's in my own best interests. I think lots of people lie to their doctors, and it makes a doctor's job much harder.

I also try to tell myself the truth, but it's probably as easy to fool myself as anyone.