Civil Engineering Reference
In-Depth Information
Now Equation (9.15) can be used to calculate the average arm length (acromion to wrist, AW):
m
AW
¼
m
A
m
W
¼
1455
:
75 mm
857
:
1mm
¼
598
:
65 mm
:
According to Equation (9.16), the standard deviation of that arm length is
6
2
9
2
9)
1=2
mm
S
AW
¼
(59
:
þ
37
:
2
0
:
3
59
:
6
37
:
¼
60
:
3mm
:
Example 3: What is the mass of the head of a 75p Japanese female? The mass (weight) of the total body
has a mean of 54.0 kg and a standard deviation of 6.0 kg — see Table 9.5. The estimated mass of the head
is 6.2% of the total body mass (from data compiled by Kroemer et al. 1997). One can assume that the
correlation coefficient between the masses of head and total body to be 1. (That assumption may be
challenged, though.)
The mean head mass is, of course,
Mean mass (m
head
)
¼
0
:
062
54
:
0kg
¼
3
:
35 kg
:
The scaling factor E is, according to Equation (9.2):
E
¼
S
total body
=
m
total body
¼
6
:
0kg
=
54
:
0kg
¼
0
:
11
:
The standard deviation of the head mass is calculated from Equation (9.4):
S
head
¼
3
:
35 kg
0
:
11
¼
0
:
37 kg
:
According to Equation (9.1), the mass of a 75th percentile head is (with k
¼
0
:
67 taken from Table 9.2)
mass
head75
¼
3
:
35 kg
þ
0
:
67
0
:
37 kg
¼
3
:
6kg
:
9.8 The “Normative” Adult versus “Real Persons”
Without formally stating so, even without consciously being aware of it, we commonly design for a group
of “regular” people who are in the 25- to 45-yr age bracket; who are of “normal” anthropometry, that is,
have body dimensions such as stature, hand reach, or weight close to the 50th percentile; who are
“healthy” in their metabolic, circulatory, and respiratory subsystems; whose nervous control, sensory
capabilities, and intelligence are all “near average,” and who are able and willing to perform “normally.”
Thus, by default or for reasons, the normative stereotype of many human factor engineers is the “regular”
adult woman or man. (This prototype seems to be a close relative of the mysterious “average person” who
appears in speeches of politicians, in newspapers, and in some flawed design models.)
This normative adult has become our prototype to which we compare other subgroups, such as chil-
dren, temporarily or permanently impaired persons, women during their pregnancy, or aging people
(Kroemer, 2006). Yet, most individuals and whole population subgroups deviate in size, strength, or
other performance capabilities from the adult norm. In reality, hardly a person exists who is average
in most or all respects; consequently products or processes “designed for the average” fit nobody well
(Kroemer et al., 2001). To achieve ease, efficiency, and safety, it is mandatory to consider the ranges
of, the variations in, and the combinations of physiologic and psychologic traits; the foregoing discus-
sions showed ways to accommodate anthropometric variability.
Search WWH ::
Custom Search