By Charles Seife
If you want to convince the world that a fish can sense your emotions, only one statistical measure will suffice: the p-value.
The p-value is an all-purpose measure that scientists often use to determine whether or not an experimental result is “statistically significant.” Unfortunately, sometimes the test does not work as advertised, and researchers imbue an observation with great significance when in fact it might be a worthless fluke.
Say you’ve performed a scientific experiment testing a new heart attack drug against a placebo. At the end of the trial, you compare the two groups. Lo and behold, the patients who took the drug had fewer heart attacks than those who took the placebo. Success! The drug works!
Well, maybe not. There is a 50 percent chance that even if the drug is completely ineffective, patients taking it will do better than those taking the placebo. (After all, one group has to do better than the other; it’s a toss-up whether the drug group or placebo group will come up on top.)
[...]
The same applies to a well-publicized study that a team of neuroscientists once conducted on a salmon. When they presented the fish with pictures of people expressing emotions, regions of the salmon’s brain lit up. The result was statistically significant with a p-value of less than 0.001; however, as the researchers argued, there are so many possible patterns that a statistically significant result was virtually guaranteed, so the result was totally worthless. p-value notwithstanding, there was no way that the fish could have reacted to human emotions. The salmon in the fMRI happened to be dead.
|