False precision
From Wikipedia, the free encyclopedia
False precision occurs when numerical data are presented in a manner that implies better precision than is actually the case; since precision is a limit to accuracy, this often leads to overconfidence in the accuracy as well.
In science and engineering, convention dictates that unless a margin of error is explicitly stated, the number of significant figures used in the presentation of data should be limited by the precision of those data. Even outside these disciplines, there is a tendency to assume that all the non-zero digits of a number are meaningful; thus, providing excessive figures may lead the viewer to expect better precision than actually exists.
False precision commonly arises when high-precision and low-precision data are combined, and in conversion of units. Examples:
- “Bobo the Elephant weighs 10 tonnes. I weigh 79 kilograms. Together, Bobo and I weigh 10,079 kg.”
- “There were about two hundred people at the party when it started. Three of them left early, so we should set one hundred and ninety-seven places for dinner.”
- “Two years ago an article was published stating that the dinosaurs died out 65 million years prior, which means the dinosaurs died out 65,000,002 years ago.”
- “European authorities estimated that the bomb used 110 pounds of explosive.” In this example, European authorities, which express measurements in SI units (the metric system), estimated that the bomb used 50 kg of explosives. Such estimates are necessarily subject to great uncertainty. When converted by the American media to pounds, the new value suggests greater accuracy in the estimation of the bomb’s size than actual.
- In the United States, normal human body temperature is commonly quoted with false precision as 98.6 °F (37.0 °C). In Russia, the commonly quoted value is 36.6 °C (97.88 °F). These values appear to be the result of the same classic German study that found the average body temperature of healthy humans is 36.6 °C. Because of the normal variation in human body temperature, this value would properly be rounded to 37 °C or 98 °F. One commonly cited normal range for human body temperature is 36.4 – 37.1 °C (97.5 – 98.8 °F).
