Supplement
H Measuring Output Rates
1. Work Standards
• Work measurement as a management tool
o Managing processes and supply chains
o How they are used
• Work Standards
1. Developing a Work Standard
2. Methods of Measuring Output Rates
2. Time Study Method
1. Time study is:
a. Steps in a time study Examples H.1 and H.3
• Step 1. Selecting work elements
• Step 2. Timing the elements
• Step 3. Determining sample size
• Step 4. Setting the standard
b. Application H.1: Time Study Method
Lucy and Ethel have repetitive jobs at the candy factory. Management desires to
establish a time standard for this work for which they can be 95% confident to be within
± 6% of the true mean. There are three work elements involved:
Step 1: Selecting work elements.
#1: Pick up wrapper paper and wrap one piece of candy.
#2: Put candy in a box, one at a time.
#3: When the box is full (4 pieces), close it and place on conveyor.
Step 2: Timing the elements.
Select an average trained worker: Lucy will suffice.
Element
Initial Observation Cycle Number, Minutes
Select
Time,
t
Standard
Dev,
1
2
3
4
5
6
7
8
9
Wrap #1:
0.10
0.08
0.08
0.12
0.10
0.10
0.12
0.09
0.11
Pack #2:
0.10
0.08
0.08
0.11
0.06
0.98*
0.17
0.11
0.09
Close #3:
0.27
…
…
…
0.34
…
…
…
0.29
* Lucy had some rare and unusual difficulties; don‘t use this observation.
Step 3: Determining sample size.
First calculate
t
for each element in Step 2. Then determine the sample size,
assuming a 95% confidence interval, with z =1.96. The precision interval of ±
6% of the true mean implies p = 0.06.
Step 4: Setting the standard.
Determine the normal time (NT) for each work element, given the rating
factors in the table. Then determine the normal time for the whole cycle and
then the standard time, assuming an allowance of 18.5%.
Element
Select Time,
t
Frequency
Rating
Factor
Normal
Time
Wrap #1:
1.00
1.2
Pack #2:
1.00
0.9
Close #3:
0.25*
0.8
* Note that for the third element, the frequency is 0.25 because the box is
closed only once every four cycles.
2
2
z
npt
= = =
Determine the normal time for the cycle.
Subjectively determine the proportion of the normal time to be added for
allowance, and then calculate standard time ST. Let the allowances be 18.5% of
the normal time.
c. Overall assessment of time study
3. Elemental Standard Data Method
• Useful for processes with high divergence, but when basic elements of work for different
services and processes are similar.
• The basic approach
4. Predetermined Data Approach
• Break each work element into micromotions: reach, move, disengage, apply pressure, grasp,
position, release, and turn.
• The basic approach
o Step 1: Break each work element into its basic micromotions – reach, move, disengage,
apply pressure, grasp, position, release, and turn.
o Step 2: Find tabular value of time for each micromotion, accounting for mitigating
factors: weight, distance, size, degree of difficulty.
o Step 3: Normal times of micromotions are added for the task.
o Step 4: Adjust for allowances to arrive at the standard time.
• Advantages
• Disadvantages
5. Work Sampling Method
• Results in a proportion of time spent doing an activity, rather than a standard time for the
work.
1. Work Sampling Procedure: Basic approach Example H.4
a. Step 1. Define the activities.
b. Step 2. Design the observation form.
c. Step 3. Determine the length of the study.
d. Step 4. Determine the initial sample size.
e. Step 5. Select random observation times.
f. Step 6. Determine observer schedule.
g. Step 7. Make observations and record data.
h. Step 8. Decide whether further sampling is required.
2. Sample Size
a. Formula:
b. Application H.2: Work Sampling Method
Major League Baseball (MLB) is concerned about excessive game duration. Batters now
spend a lot of time between pitches when they leave the box to check signals with
coaches, and then go through a lengthy routine including stretching and a variety of other
actions. Pitching routines are similarly elaborate. In order to speed up the game, it has
been proposed to prohibit batters from leaving the box and to prohibit pitchers from
leaving the mound after called balls and strikes. MLB estimates the proportion of time
spent in these delays to be 20% of the total game time. Before they institute a rules
change, MLB would like to be 95% confident that the result of a study will show a
proportion of time wasted that is accurate within ±4% of the true proportion.
Steps 1 and 2. Define the activities and design the observation form.
Step 3. Determine the length of the study. Suppose that ten games (or 32 hours) are
appropriate.
Step 4. Determine the initial sample size.
n =
æ
è
ç ö
ø
÷ 2
0.20 1 – 0.20
( )
=
Steps 5 and 6. Determine the observer schedule.
Step 7. Observe the activities and record the data.
Suppose you find 96 unacceptable delays for pitcher and 46 unacceptable delays for
batters.
Step 8. Check to see whether additional sampling is required.
For pitchers:
n =
æ
è
ç ö
ø
÷ 2
( )
1 –
( )
=
For batters:
n =
æ
è
ç ö
ø
÷ 2
( )
1 –
( )
=
Conclusion?
3. Overall assessment of work sampling
a. Advantages
b. Disadvantages
6. Managerial Considerations in Work Measurement
• Consistent with the firm’s competitive priorities
• Technological change
o Increased automation
o
o