MYP Design Anthropometric Data and Percentiles Notes

Anthropometric Data: Numbers Instead of Guesswork

1. Anthropometric data is a table of body measurements taken from thousands of real people, so you can look up a number instead of guessing from the one body you know best, your own.
2. A typical table lists stature (standing height), sitting height, shoulder breadth, elbow height, hand length, grip diameter and eye height, usually split by sex and age group.
3. Every measurement comes with a spread, because adult stature runs from roughly 1450 mm to over 1950 mm once you include the whole population.
4. Skipping the data is how you end up with a shelf at 1900 mm that half the class cannot reach and a chair that leaves shorter students' feet swinging.

Static and dynamic measurements

1. Static data is measured with the body still, such as shoulder breadth, hand length and hip width.
2. Dynamic data is measured while the body moves, such as how far an arm sweeps across a desk or how much floor space someone needs to turn a wheelchair.
3. A car dashboard needs dynamic data, because the driver is strapped into a seat and twisting, not standing relaxed against a wall.

Where Designers Actually Get the Numbers

1. Nobody runs their own national survey, so designers pull figures from published sources such as the standard BS EN ISO 7250, which sets out how each body measurement should be taken.
2. National data sets differ, and Dutch male stature sits well above Japanese male stature at the same percentile, so the country the table came from matters.
3. For a school project you can measure your own user group: 30 students measured with a metre rule, a set square and a tape gives you a real sample for a classroom product.
4. Write down exactly how you measured, because hand length taken from the wrist crease and from the base of the palm give different numbers and the two cannot be mixed in one table.

Percentiles Rank People, They Do Not Average Them

1. Line up 100 people by height with the shortest at one end, and the 5th person along marks the 5th percentile for that group.
2. So a 5th percentile stature means 5 per cent of people are shorter and 95 per cent are taller, and the figure is a boundary line drawn through the group.
3. The 50th percentile is the middle person in that line, which sits close to the mean but is not the same calculation.
4. Each measurement gets its own percentile, so a 95th percentile shoulder breadth does not arrive attached to a 95th percentile leg length.

The 5th, 50th and 95th in practice

1. UK adult female stature sits near 1505 mm at the 5th percentile and near 1610 mm at the 50th.
2. UK adult male stature sits near 1740 mm at the 50th percentile and near 1855 mm at the 95th.
3. Working between the 5th percentile female and the 95th percentile male covers roughly 90 per cent of adults, which is the usual target for a general product.
4. Stretching to the 1st and 99th percentiles costs space, material and money, so it is saved for cases where being excluded is dangerous, such as an emergency exit or a fire door handle.

Designing for the Average Fits Almost Nobody

1. Take the 50th percentile of ten different measurements and hardly any real person matches all ten at once.
2. A chair built to average seat height, average seat depth and average backrest height only fits the person who is average in all three, and that person is rare.
3. The average also hides the two tails, so a bench at average knee height leaves short users with feet dangling and tall users with knees pushed up.
4. The working method is to design for a range, then decide for each single dimension which end of that range sets the limit.
5. A range never means sizing everything for the biggest person, because a seat deep enough for a 95th percentile thigh presses into the back of a 5th percentile user's knee.

Clearance, Reach and Adjustability: Three Different Rules

1. Clearance is space the body has to pass through or sit inside, like a doorway, the legroom under a desk or the gap in a climbing frame.
2. Size clearance on the largest user, normally the 95th percentile, because once the biggest person fits everyone smaller fits as well.
3. Reach is the distance to something the user must touch, like a shelf, a light switch or a brake lever on a bike.
4. Size reach on the smallest user, normally the 5th percentile, because a shorter arm that reaches guarantees every longer arm does.
5. Adjustability covers the cases where no single fixed size works, and the travel of the adjustment runs from the 5th percentile need to the 95th percentile need.
6. Every adjustment adds cost, extra parts and one more thing to snap, so put it where fit genuinely changes how the product works rather than on every dimension.

Worked Examples: A Door, A Seat and A Handle

1. A standard UK internal door is 1981 mm high, which clears a 95th percentile male stature of about 1855 mm with room left for shoes, hair and the bounce of a walking stride.
2. That is a clearance dimension, sized on the tallest user, and nobody shorter ever complains that the door is too high.
3. Seat height is set by popliteal height, the distance from the floor to the back of the knee, so the shorter user keeps their feet flat on the floor.
4. A fixed classroom chair at around 430 mm suits mid-range secondary students, while an office chair adjusts from about 400 mm to 510 mm because the 5th and 95th percentile popliteal heights are roughly 100 mm apart.
5. For a tool handle held in a full power grip, a diameter of about 30 mm to 40 mm lets the fingers close far enough to overlap the thumb, which is where grip force peaks.
6. Push the handle out to 60 mm and a small hand can no longer wrap it, so grip force drops and the wrist ends up taking the load.