Subjective Scales of Effort and Workload Assessment - Fundamentals and Assessment Tools for Occupational Ergonomics - page 740

Difficulty Level Operator Demand Level Rating

Very easy,
Highly
desirable

Operator mental effort is
minimal and desired
performance is easily
attainable

1

Easy,
desirable

Operator mental effort is
low and desired
performance is attainable

2

Fair, mild
difficult

Acceptable operator
mental effort is required to
attain adequate
system performance

3

Minor but
annoying
difficulty

Moderately high operator
mental effort is required to
attain adequate system
performance

4

Moderately
objectionable
difficulty

High operator mental effort
is required to attain
adequate system
performance

5

Very
objectionable
but tolerable

Maximum operator mental
effort is required to attain
adequate system
performance

6

Major
difficulty

Maximum operator mental
effort is required to bring
errors to moderate level

7

Major
difficulty

Maximum operator mental
effort is required to avoid
large or numerous errors

8

Major
difficulty

Intense operator mental
effort is required to
accomplish task, but
frequent or numerous
errors persist

9

Impossible Instructed task could

not be accomplished
reliably

10

FIGURE 37.2 Modified Cooper-Harper rating scale.

estimates of mental workload. Validation research showed that the MCH scale reflects differences in both
performance and workload, and is sensitive to variations in controls, displays, and aircraft stability
(Rehman, 1995). The MCH was successfully applied to workload evaluation in many flight simulation
experiments (Casali and Wierwille, 1983, 1984; Wierwille et al., 1985; Skipper et al., 1986). The MCH
scale was able to discriminate between the low, moderate, and high communication loads and mental
loads in such tasks as different hazard detection conditions were also observed (Casali and Wierwille,
1984) and navigation dilemmas (Wierwille et al., 1985). Significant increase of MSH ratings with
increased danger conditions (Casali and Wierwille, 1984). The applications of the MCH scale in such
environments as remotely piloted vehicle system (Byers et al., 1988) and generic air defense system
(Bittner et al., 1989) confirmed sensitivity of the scale. It was concluded that the MCH scale provides
consistent and sensitive ratings of workload across a range of tasks (Wierwille et al., 1985; Skipper
et al., 1996). However, some studies showed that the MCH is less sensitive than the NASA TLX or the
overall workload scale (Hill et al., 1992).

37.4.4 Workload Profile
The Workload Profile (WP) is a relatively new multidimensional workload assessment technique (Tsang
and Velazquez, 1996). The workload dimensions assessed by this instrument are based on the resource