Time Study Method
•
•
•
•
Step 1 ...
Step 2 ...
Step 3 ...
Step 4 ...
Selecting Work Elements
Timing the Elements
Determining Sample Size
Setting the Standard
Step 1
Selecting Work Elements
• Definite starting and
stopping points
• Correspond to a standard
work method
Step 2
Timing the Elements
• Analyst times a worker
– Continuous method
– Snap-back method
• “ Irregular occurance “
• Select time (t)
Step 3 ... Determining Sample Size
• Average time estimate close to
1/2
true long range average
• n = [(z/p)(σ/t)]²
–
–
–
–
–
n = required sample size
p = precision of the estimate as a proportion of the true value
t = select time for a work element (w.e.)
σ = standard deviation of representative observed times for a w.e.
z = number of normal standard deviation needed for the desired
confidence
• Fallbeispiel:
Workelement Standard deviation Select Time Sample Size
Get two cartons
0.0305
0.50
5
Put liner in carton
0.0171
0.11
10
Place cups in cart.
0.0226
0.71
10
Seal carton
0.0241
1.10
10
Step 3 ... Determining Sample Size
2/2
Sample size of each Work Element
• Work Element 1
n = [(1.96/0.04) (0.0305/0.500)]²
= 9
n = [(1.96/0.04) (0.0171/0.11)]²
= 58
n = [(1.96/0.04) (0.0226/0.71)]²
= 3
n = [(1.96/0.04) (0.0241/1.10)]²
= 2
• Work Element 2
• Work Element 3
• Work Element 4
Step 4 ... Setting the Standard
1/3
• Normal time for each work element
NT = t(F)(RF)
– Perfomance rating factor (RF)
– Frequency of occurance (F)
• Normal time for the cycle (NTC)
NTC = ΣNT
• Fallbeispiel:
Workelement
Get two cartons
Put liner in carton
Place cups in cart.
Seal carton
t
0.53
0.10
0.75
1.08
F
0.50
1.00
1.00
1.00
RF
1.05
0.95
1.10
0.90
Step 4 ... Setting the Standard
2/3
Normal Times of each Work Element
• Work Element 1
NT1 = 0.53(0.50)(1.05) = 0.28 minute
• Work Element 2
NT2 = 0.10(1.00)(0.95) = 0.10 minute
• Work Element 3
NT3 = 0.75(1.00)(1.10) = 0.83 minute
• Work Element 4
NT4 = 1.08(1.00)(0.90) = 0.97 minute
Total = 2.18 minutes
Step 4 ... Setting the Standard
• Allowance Time:
3/3
ST = NTC(1 + A)
• Standard time for the coffee cup packaging operation
Solution for A = 0.15
ST = 2.18(1 + 0.15) = 2.51 minutes/carton
Production standard for eight-hour day
(480 minutes/day) / (2.51 minutes/day) = 191 cartons/day
• Overall Assessment of Time Study
–
–
–
–
Not useful for tasks that are different each time
Inexperienced persons should not conduct time studies
Subjectivity is involved
BUT: Conducted by experienced observers 
satisfactory tool for setting equitable time standards
3 Methods
• Elemental Standard Data Approach
• Predetermined Data Approach
• Work Sampling
Elemental Standard Data Approach
-- Highlights -• Decreases the number of time studies
• Time studies are saved as elemental standard data in a
database
• Define other job standards
• Job standards before production begins
Elemental Standard Data Approach
-- Attention! --
• Does not eliminate time studies!
• Check new job standards from time to time
(gap between theory an reality).
• Not the best method
Predetermined Data Approach
• No time studies.
• Micromotions instead of work elements
• Time unit for a micromotion is Time
Measurement Unit (TMU)
1 TMU = 0.0006 minute = 36ms
• Get TMUs from public databases (i.e. Methods
Time Measurement (MTM)-databases like MTM1).
Basic micromotions in MTM-1 are
reach, move, position, turn, release,…
Predetermined Data Approach
-- Steps to the job standard -1. Divide each work element into micromotions
2. Find a database for the micromotions’ values
(TMUs, factors,…)
3. Sum up the normal times for each micromotion
(= normal time)
4. Calculate the standard time with the normal
time and the allowances (factors, constant
values).
Predetermined Data Approach
-- Example --
A worker has to move an 18 pound object to
an exact location 20 inches away.
Predetermined Data Approach
-- Table 1 – MTM predetermined Data for the Move Micromotion -Distance Moved
(in.)
A
B
C
Hand in Motion B
3/4 or less
2
2
2
1,7
1
2,5
2,9
3,4
2,3
2
3,6
4,6
5,2
2,9
3
4,9
5,7
6,7
3,6
4
6,1
6,9
8
4,3
5
7,3
8
9,2
5
6
8,1
8,9
10,3
5,7
7
8,9
9,7
11,1
6,5
8
9,7
10,6
11,8
7,2
9
10,5
11,5
12,7
7,9
10
11,3
12,2
13,5
8,6
12
12,9
13,4
15,2
10
Wt. (lb.) Up to
Dynamic Factor
Static Constant (TMU)
14
14,4
14,6
16,9
11,4
2,5
1
0
16
16
15,8
18,7
12,8
7,5
1,06
2,2
18
17,6
17
20,4
14,2
12,5
1,11
3,9
20
19,2
18,2
22,1
15,6
17,5
1,17
5,6
22
20,8
19,4
23,8
17
22,5
1,22
7,4
24
22,4
20,6
25,5
18,4
27,5
1,28
9,1
26
24
21,8
27,3
19,8
32,5
1,33
10,8
28
25,5
23,1
29
21,2
37,5
1,39
12,5
30
27,1
24,3
30,7
22,7
42,5
1,44
14,3
Additional
0,8
0,6
0,85
TMUs per inch 30+
47,5
1,5
16
Case
Description
A
Move object to other hand or against stop
B
Move object to approximate or indefinite location.
C
Move object to exact location
22.1 * 1.11 + 3,9 = 28 TMUs
Weight Allowance
Predetermined Data Approach
++
• Job standards before production begins
• Compare work methods without time
studies
• Consistency in setting time standards (i.e.
no recording errors from time studies)
• Biased judgment is eliminated
• No time studies
Predetermined Data Approach
-• Dividing work element into micromotions
• Impractical for products and services with low
repeatability
• Micromotions may not fit exactly to the work
• Not all data are in the databases (i.e. the shape of
an object).
• The sum of the micromotions may not fit to the
time really needed for the job (gap between theory
and reality)
• Misuse of the method
Work Sampling Method
-- Goals/Possibilities --
• Time which is needed for a specific activity
by a worker or machine.
• Effectiveness of machines or workers
• Job content
• Cost of jobs or activities
• Allowance time for the 2 Methods above
(i.e. resting time, fatigue,..)
Work Sampling Method
-- Procedure -1.
2.
3.
4.
5.
6.
7.
8.
Activities (what is going to be measured?)
Observation form
Length of the study
Sample size
Observation times
Observer schedule
Observe the activities and record the data
Additional sampling is required?
Work Sampling Method
-- defining activities -Activities could be …
•
•
•
•
Producing a product or service
Doing paperwork
Waiting for instructions
Being idle
Work Sampling Method
-- sample size -Estimate the proportion of time spent on a specific
activity, which doesn’t differ from the true proportion
by more than an error e.
pe  p  pe
p ...... Sample proportion (number of positive
divided by sample size)
e …… maximum error in the estimate
Work Sampling Method
Binomial distribution of the sampling and a
big sample size
Approximation to a normal distribution to
determine the sample size.
Work Sampling Method
-- sample size -The sample size affects the degree of precision
p  1 - p 
ez
n
z
n   
e
2
 p  1 - p
n …… sample size
z …… number of standard deviations needed to achieve
the desired confidence
Work Sampling Method
-- Example -• Medical records storage and retrieval system
• Determine Advisability of Purchase
• Registered Nurses – RNs
• Licensed Vocational Nurses – LVNs
• Ward staffed by 8 RNs and 4 LVNs
• Proportion of time spent accessing records
Work Sampling Method
-- Example -• Time spent accessing records takes estimated about
20 % of RNs and
5 % of LVNs time
• Requirement:
95 % Confidence
that the estimate falls within
+ 0.03
of true proportion
• Sample size ???
Work Sampling Method
-- Example -Desired
Confidence (%)
90
95
96
97
98
99
• RN:
• LVN:
z
1,65
1,96
2,05
2,17
2,33
2,58
z
n   
e
2
 p  1 - p
2
 1.96 
n
  0.20  0.80  683
 0.03 
2
 1.96 
n
  0.05  0.95  203
 0.03 
Work Sampling Method
-- Example -8 RNs and 4 LVNs can be observed on each trip
RNs:
683
 86 trips
8
203
LVNs: 4  51 trips
 688 observations of RNs
344 observations of LVNs
Work Sampling Method
-- Example -Activity
Accessing
Records
Attending to
Patients
Other support
activities
Idle or
break
Total
observations
124
258
223
83
688
28
251
46
19
344
RN
LVN
Results of the Initial Study
Work Sampling Method
-- Example -• Annual amortization costs for the new system
150.000 $ (estimated)
• System reduces time nurses spend accessing records by
25 % (estimated)
• Total anual salary expense
RNs
3.628.000 $
LVNs 2.375.000 $
• Nurses could use productively time saved by system
Work Sampling Method
-- Example -Additional Sampling required ??
RNs 124  0.1802
LVNs
28  0.0814
Accessing
Records
Total
observations
124
688
28
344
RN
LVN
Original estimates off the mark

2
 1.96 
n
  0.1802  0.8198  631
0
.
03


sample size smaller
FaultTolerance + 0.03  between 0.15 and 0.21
Work Sampling Method
-- Example --
Workgroup
Total
Observation
Activity
Observation
Proportion of
Total
Confidence
Lower
Confidence
Upper
Required
Sample Size
688
124
0,1802
0,1515
0,209
631
344
28
0,0814
0,0525
0,1103
320
RN
LVN
Work Sampling Method
-- Example -• Net Savings:
0.25[(3.628.000$)(0.18) + (2.375.000$)(0.08)]
- 150.000$
= 60.760$
• Worst Case 0.15 (RNs) & 0.05 (LVNs)
• Net Savings
0.25[(3.628.000$)(0.15) + (2.375.000$)(0.05)]
- 150.000$
= 15.737$
The new System appears
to be a good investement !!!
Work Sampling Method
-- Overall Assesment -Advantages:
 No special training required
 No stopwatches needed
 Simultaneous Studies
 activities of groups, rather than individuals
Major Disadvantage
 Large number of brief observations