When Positives are False and Negatives are Right

Often claims are made in the media about scientific or medical results that we tend to believe, because they are based on statistics and have been published by reputed scientists. But regrettably, the claims can be wrong, because of problems known as false positives and false negatives. Here is one example. You may have heard that there are about 100 deaths every year in the USA attributed to bee stings, which is far fewer than deaths caused by venomous snakes. Statistics don’t lie; at least that is what one is taught and so people believe this is a fact and conclude that bees are more dangerous than snakes, or worse, accept that the bee venom is more potent than that of snakes. However, the fact that more people are likely to die from a bee sting than a snake bite is based on an unequal comparison: far more people get stung by bees (and survive) than are bitten by snakes (and don’t survive). To therefore conclude that bees are more dangerous than snakes is a false positive  –  or at least not the full truth.

Let’s look at a false negative and stay with some insects. Assuming a pest eradication programme to rid a plantation of a species that attacks a particular crop is declared to have been 100% successful: no pest insects are found during the entire summer. The farmer sees the results of the study and is happy: the pest is gone he is told to believe. The scientists explain that no eggs would have been laid at all, because all the adults had been killed and there shouldn’t be any offspring the next year. But in the following year the pest is back. The conclusion was a negative positive, because it hadn’t been considered that some eggs may enter a period of several years of dormancy and could have been laid some years before the eradication programme occurred. Similarly, the conclusion based on thorough searches that some species had become extinct has sometimes been proven wrong: a negative false positive. That a person after a blood test is told s/he is suffering from diabetes can be a false positive, if it is not considered that the tested person might have had a snack some time before the test and forgot to mention that. And how about this: far more men attend demonstrations than women. The conclusion that women are therefore more content, complain less and lead easier lives than men: a false positive or correct result?

It has been shown in a 2015 study by Tajika et al. that in the medical sciences 50% of the reported results could not be replicated and many would be false positives or false negatives. Sometimes false positives and false negatives seem unavoidable in scientific research, because some contributing factors could not be considered, because they were not known. Examining the ratio between male and females of an insect species can be important, but sometimes the results suffer from false positives or negatives. If collections with light traps are made and one catches 80% males and only 20% females and then concludes that four times more males than females occur in the population, one may be quite wrong, not having considered that females may fly less or are less strongly attracted to the light trap. Shaking trees and collecting and sexing the beetles that have dropped is another method to determine sex-ratios. This collecting method may reveal a dominance of females as they seek to protect themselves more readily by dropping down, but the sex ratio may well have been 50:50 as male individuals might cling more tightly to the leaves and don’t drop or have become easier prey of spiders and birds, so that the conclusion that in this species the sex ratio is biased towards females is a false positive.

Where it seems to be more advisable to accept a false negative is in the criminal court. There is always the fear that a false positive leads to a conviction of someone who is actually innocent, and the alternative, namely to find someone not guilty when the person in reality is, is seen as something more easily acceptable. I love ice cream and chocolate and, being slim, I tell myself that their consumption is said to lead to obesity is a false positive, whether right or wrong. You are getting the point, right?

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content. 

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