Some doubt might be cast on the general validity of the results by the following brief description of the experiment being reported here:
"In the study, 40 wallets were sent out in each photograph category as well as 40 containing a card suggesting that the owner had recently made a contribution to charity. A control batch contained no additional item.
All of the wallets were stuffed with the same set of everyday items, including raffle tickets, discount vouchers, and membership cards. None of them contained money, however."
I think that since there was nothing valuable inside, finders might have thought it was not worth the trouble sending the wallets back, while a baby picture is valuable to its owner, so it was worth sending back. If I had found such a wallet, that's the way I would have acted.
I was actually thinking the complete opposite. Since they found nothing of value in the wallets, they were easy to part with and send back. If they found $300 in cash, the finder may have felt more inclined to keep the wallet or at least the money. A good follow up test would be to see how often the money comes back with the wallet.
I was not trying to speculate what people would do if they found a wallet full of money, I was just trying to interpret why they sent back a wallet with a baby picture but did not send back a wallet with nothing of value inside.
That is such a small sample size that the results could be masking underlying probabilities world wide. This study certainly has no meaning to places like Saudi Arabia where it is illegal to touch a dropped wallet unless you are the security staff of the building, the police, or an agent of the owner. Imagine if they did the exact same experiment there.
Note that that's 40 wallets in each of 6 categories; the total number was 240.
If half of all wallets get returned, then the variance of the number returned is on the order of 40 * 1/2 * (1-1/2) = 10, which means a standard deviation on the order of 3 wallets returned, or ~ 8% return rate. So the "puppy" and "family" figures might be out by about that much.
The cute-baby category had a measured return rate of 88%, which means a variance of something like 40 * 0.88 * 0.12~=4.2, for a standard deviation of ~ 2 wallets or about 5% in the return rate.
So if these results are unlucky to the tune of two 2-sigma errors pointing in the "right" direction, the puppy category might really be as good as 69%, and the baby category might really be as bad as 78%.
So, at least as far as simple sampling error goes, the "baby beats puppies" result seems pretty robust.
(No need to tell me about all the oversimplifications in the above. I know.)
I sympathize with what you are trying to do, but you are right when you say oversimplifications abound. I do Market/Business Intelligence for a living. I repeatably see the results of split tests change drastically after 100 results per option come in, I have even seen 1000 samples per option change. Human beings don't always fit into a nice standard deviation. A holiday, or the weather, or unknown variable X will just go ahead and mess everything up for you. Sure, if I had to make a decision based JUST on this data I would keep a baby instead of a puppy, but I wouldn't be nearly as confident as the article writer is.
How do statisticians decide on what a good sample size is?
Certainly they can't use the science of statistics to determine the sample size, since a good statistical study would require using a good sample size.
I don't like the way this article presents the viewpoint of evolutionary psychology. A conception such as morality vs evolution is nothing short of dangerous.
I think this is a probable scenario:
"Oh, look, a wallet. I wonder what's inside... Alright, no money anyway. Some tickets and shit. Should I return it? Can I be bothered? Must be a real hassle for the owner with all these cards of course. - Oh, a picture of a baby. I bet this person is stressed out with the kid as it is. Hey, might as well be a Good Samaritan today..."
Yeah. I love how they ask a professor to tack a completely spurious evolutionary explanation on there. You know, a speculation coming from a professor on the basis of a sound scientific theory is still just a speculation.
On the whole, I wish people didn't feel the need to jazz up empirical results with that kind of pseudo-technical commentary. It muddies the reader's mind about which part actually constitutes the science.
My first thoughts too. Why does everything in psychology/social has to be tied to evolution these days?
Once upon a time, you did it because someone told you too. Then, some god. Later, because you're of a certain class.
Today, we're doing it because it helps the "evolution". This is nice, if you know why the evolution does what it does. Which is turtle all the way down.
Shit, something helps us to last longer as a species? It's the answer. If we know how it helps us.
Heck, I'll throw an evolutionary bias into this research. Why should I help another male? It's my desire that he fails so I can own the offspring-maker. (yes, I'm aware of some studies that show cooperation is better for the group. WITH FISHES).
"For evolutionary reasons" is the new thing on social studies. 3pt14159's comment is spot on http://news.ycombinator.com/item?id=700571 this study has too many random variables to have any credulity.
"Scientists argue that it would be difficult to genetically code for feeling empathy exclusively towards your own child and much easier to code for feeling empathy towards all children."
Aren't there several species that do in fact shun the offspring of other parents?
I think that the different feelings toward different families are based on pheremones, not sight, so it wouldn't really come into play with just a photo.
Those are very, very logically distinct, species and tribe, I mean. You can conceivably have people doing things for the good of the tribe because in a natural environment they're probably related to the other members of the tribe so if the behaviour helps teh sponsoring gene spread, on average it will propagate. "It's good for the species" is never a good explanation for anything, ever. The other members of of a species (of one's own sex) are the competition, the ones you want to fail in comparision to you. Group selection works fine if there's a guiding intelligence behind it, but there are no examples in nature, ttbomk.
While there may be advantages to carrying a photo of someone else's kid in your wallet, the difficult questions and embarrassing situations that are going to come up from that are just not worth it.
I have pictures of my nieces and nephews, and friends babies in my wallet- why would there be any embarrassment or difficult questions as a result of this?
See, if you reach for your wallet to pay for dinner, and your date/business colleague says, "oh, what a cute photo! Is that your kid?," you can just say, "no, that's my nephew," and still beam with pride. I, however, would have to say, "no, that's some kid whose photo I downloaded from Flickr; isn't he adorable?" and the awkward conversation would not end there.
"In the study, 40 wallets were sent out in each photograph category as well as 40 containing a card suggesting that the owner had recently made a contribution to charity. A control batch contained no additional item.
All of the wallets were stuffed with the same set of everyday items, including raffle tickets, discount vouchers, and membership cards. None of them contained money, however."
(Added italics mine.)