False precision
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Template:Unreferenced 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 10000 kilograms. I weigh 79 kilograms. Therefore, if I sat on Bobo, we would weigh 10079 kilograms.'
- '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.'
- The Wikipedia article Mikoyan-Gurevich MiG-21 once stated this fighter plane's thrust at 69.58 kN and 15,650 lbf. This is a trickier one; just looking at those numbers does not suggest false precision, since both the metric and imperial values are given to the same degree of precision. However, both of these numbers are the result of conversion from an unstated original in units different from either of the ones stated here: 7,100 kilograms-force, which only has two significant digits of precision. Multiplying by 9.8 m/s² converts this figure to 69,580 newtons, and 7,100 kgf multiplied by 2.2046 lbf/kgf yields 15652.66 lbf, rounded slightly but not enough. Note that even if the measurement of the thrust were 7.100 megagrams-force, with both zeros significant, the conversion factor used to convert kgf to kN is not precise enough to get 4 significant digits in the result (the exact conversion factor is 1 kgf = 9.80665 N).
- Normal human body temperature is commonly quoted with false precision as 98.6°F (which equals 37.0 °C) in the United States, but as 36.6 °C (which equals 97.88°F) in Russia. Both numbers appear to be the result of the same classic German study which found the average body temperature of healthy humans to be 36.6 °C. Because of the normal variation in human body temperature, this number is properly rounded to 37 °C. A more proper conversion to Fahrenheit would be 98°F. One commonly cited normal range for human body temperature is 36.4 - 37.1 °C (97.6 - 98.8 °F).