Know More - Definition of Anthropometry
Anthropometry measures all physical aspects of your body. Simple measurements include height and width. But a more thorough body of measurements is usually needed for Human Factors work. Measurements such as the length from your elbow to the tip of your finger or the circumference of your skull are some examples. In a complete anthropometric survey measurements are taken between every joint and across hinge joints (such as the knee and elbow). Range of motion is also recorded. Thickness or girth is measured as well.
So what can you use this data for? Well, if you need an outfit tailored your all set. But from a Human Factors perspective having anthropometric data for a single individual is only useful if you are designing something specific to that individual, such as a prosthetic limb. The real power comes from a statistical data set for a population.
A statistical data set for a population is basically measurements of a lot of people. If you have data from a statistically significant portion of a population you can extrapolate the data you don't have. So, through statistics, you can measure a few people and have enough knowledge to determine what the rest will be like with a high degree of accuracy. Much the same as an exit poll can tell us who is elected before all the votes are even cast in an election.
The population can be as general as "men", which represents all the males in the world across all races and countries. Or it can be tailored to a tighter demographic such as "Caucasian American Men".
So now you have defined your anthropometric data set. What's it good for? Much like marketing uses a demographic to tailor its message for better sales a Human Factors analysis can use a demographic for a more accurate result. In this case we bring in the percentile.
If you've had children you've used anthropometrics. Every time the pediatrician measures your child they tell you the kid is 80th percentile in height and 75th percentile in weight (or some such number). The percentile means that that percent of the population is that size or smaller for the given measurement. So an 80th percentile in height means that the child is as tall or taller than 80% of the population.
Doctors use these numbers to help determine if the child is growing within established boundaries for the population. If development is in the extremes then the doctor may be concerned and look for any potential health issues causing the abnormal growth.
Every car on the street has been designed to accommodate the largest set of the population based on an anthropometric range so that most people are comfortable in the seat and can reach the radio, for example. Again, there are countless applications for anthropometric data sets but they usually center on designing or evaluating for a range in that data set.
The data set follows a bell curve if plotted by number of occurrences. That means that there are more people at the 50th percentile and only a few at the extremes of 5% and 95% moving almost to nothing for 1% and 99%. In fact, most often the range is set between 5% and 95% because there are so few people within the extremes and the extra variation needed to compensate for that range is not deemed prudent.
In any given population on the planet women are smaller than men, so if the population set is for both men and women then the smallest extreme is the 5th percentile woman with the larger extreme being the 95th percentile male. This is the most common anthropometric range used when "everyone" needs to be able to do whatever is being looked at. If it is not required that "everyone" needs to do it, but only most then the 50th percentile is commonly used meaning that about half of the population is supported.
The 50th percentile is often considered a fallacy within Human Factors. Since it represents half of the population some have termed this the "average" person. However, hardly anybody exists that has all of the individual measurements of the body at or close to the 50th percentile. As such there is no 50th percentile. The average person doesn't exist.