Thursday, August 25, 2016

Consequences of statistical ignorance

In a study performed a few years ago [1], the following problem was proposed to 18 expert consultants for AIDS patients:
Helen has tested positive for AIDS. How likely do you think she is really an AIDS patient? What would you advise her?

The input data are:
1.      The probability of having AIDS, when one belongs to a population without special risk, is 1 in 10,000.
2.      The sensitivity of the AIDS test is 99.9%. In other words, the probability of a false negative is 0.1%.
3.      The specificity of the AIDS test is 99.99%. In other words, the probability of a false positive is 0.01%.

The result of the study was as follows:

·         The 18 experts agreed that the probability that Helen is an AIDS patient is greater than 90%. Most thought that the probability is greater than 99%. Some even claimed that is greater than 99.9%.
·         All experts said that they would advise Helen to inform her family, make everybody test for AIDS, and start taking medication.

Thursday, August 18, 2016

Science or speculation?

Merging of two black holes
In December 2013 several media made reference to an article published in the journal Physical Review Letters, in the field called quantum gravity, a set of mutually incompatible theories that in the last 30 years have scarcely formulated a single testable prediction, although they are usually presented as the latest in physics and give rise to news broadly popularized by the general media. This scientific news was presented by some media with this title: quantum entanglement causes the appearance of wormholes. Some of the reviews contained important mistakes. I’ll cite two:
1.      The group showed that, by creating two black holes intertwined, later separated, a wormhole appeared, a “shortcut”' through the universe, connecting the two distant black holes to one another.
Comment: the group did not show that. It just found some equations that suggest that this might happen (or not, because mathematics is not the same as physics). Moreover, these theoretical speculations are based on string theory, which is just one among several alternative proposals of quantum gravity existing today.

Thursday, August 11, 2016

Happy anniversary

Tomorrow August 12th is the second anniversary of the opening of this blog on popular science. The Spanish version of the blog appeared a little earlier, on January 15th 2014. In these two years I have published over 100 articles, usually one per week, although I have interrupted publication during the summer, and slowed it somewhat in Christmas.
In this anniversary I want to take stock of what has been done so far, and the goals I imposed myself when I started this activity. The decision on whether I have achieved any of these goals is left open to the consideration and critical judgment of the readers.