Time Study Method

• Step 1 ... Selecting Work Elements

• Step 2 ... Timing the Elements

• Step 3 ... Determining Sample Size

• Step 4 ... Setting the Standard

Step 1 Step 2Selecting Work Elements Timing the Elements

• Definite starting and stopping points

• Correspond to a standard work method

• Analyst times a worker– Continuous method

– Snap-back method

• “ Irregular occurance “

• Select time (t)

Step 3 ... Determining Sample Size 1/2

• Average time estimate close to 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 SizeGet two cartons 0.0305 0.50 5Put liner in carton 0.0171 0.11 10Place cups in cart. 0.0226 0.71 10Seal carton 0.0241 1.10 10

Step 3 ... Determining Sample Size 2/2

Sample size of each Work Element

• Work Element 1n = [(1.96/0.04) (0.0305/0.500)]² = 9

• Work Element 2n = [(1.96/0.04) (0.0171/0.11)]² =

58

• Work Element 3n = [(1.96/0.04) (0.0226/0.71)]² = 3

• Work Element 4n = [(1.96/0.04) (0.0241/1.10)]² = 2

Step 4 ... Setting the Standard 1/3

• Normal time for each work elementNT = t(F)(RF)– Perfomance rating factor (RF)– Frequency of occurance (F)

• Normal time for the cycle (NTC)NTC = ΣNT

• Fallbeispiel:Workelement t F RF Get two cartons 0.53 0.50 1.05Put liner in carton 0.10 1.00 0.95Place cups in cart. 0.75 1.00 1.10Seal carton 1.08 1.00 0.90

Step 4 ... Setting the Standard 2/3

Normal Times of each Work Element

• Work Element 1NT1 = 0.53(0.50)(1.05) = 0.28 minute

• Work Element 2NT2 = 0.10(1.00)(0.95) = 0.10 minute

• Work Element 3NT3 = 0.75(1.00)(1.10) = 0.83 minute

• Work Element 4NT4 = 1.08(1.00)(0.90) = 0.97 minute

Total = 2.18 minutes

Step 4 ... Setting the Standard 3/3

• Allowance Time: ST = NTC(1 + A)

• Standard time for the coffee cup packaging operation

Solution for A = 0.15ST = 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 MTM-1).

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

14 14,4 14,6 16,9 11,4

16 16 15,8 18,7 12,8

18 17,6 17 20,4 14,2

20 19,2 18,2 22,1 15,6

22 20,8 19,4 23,8 17

24 22,4 20,6 25,5 18,4

26 24 21,8 27,3 19,8

28 25,5 23,1 29 21,2

30 27,1 24,3 30,7 22,7

Additional 0,8 0,6 0,85 TMUs per inch 30+

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

Weight Allowance

Wt. (lb.) Up to Dynamic Factor Static Constant (TMU)

2,5 1 0

7,5 1,06 2,2

12,5 1,11 3,9

17,5 1,17 5,6

22,5 1,22 7,4

27,5 1,28 9,1

32,5 1,33 10,8

37,5 1,39 12,5

42,5 1,44 14,3

47,5 1,5 16

22.1 * 1.11 + 3,9 = 28 TMUs

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. Activities (what is going to be measured?)

2. Observation form

3. Length of the study

4. Sample size

5. Observation times

6. Observer schedule

7. Observe the activities and record the data

8. 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 ...... Sample proportion (number of positive divided by sample size)

e …… maximum error in the estimate

eppep

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

n …… sample size

z …… number of standard deviations needed to achieve the desired confidence

n

p-1 p z e p-1 p 2

e

z n

n

p-1 p z e

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 about20 % 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 --

• RN:

• LVN:

6830.800.202

03.0

96.1

n

2030.950.052

03.0

96.1

n

p-1 p 2

e

z n

DesiredConfidence (%) z

90 1,6595 1,9696 2,0597 2,1798 2,3399 2,58

Work Sampling Method-- Example --

8 RNs and 4 LVNs can be observed on each trip

RNs: trips

LVNs: trips

688 observations of RNs 344 observations of LVNs

868

683

514

203

Work Sampling Method-- Example --

Results of the Initial Study

Activity

Accessing Records

Attending toPatients

Other supportactivities

Idle orbreak

Totalobservations

RN

124 258 223 83 688

LVN

28 251 46 19 344

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 0.1802LVNs 28 0.0814

Original estimates off the mark

sample size smaller

FaultTolerance + 0.03 between 0.15 and 0.21

Accessing Records

Totalobservations

RN

124 688

LVN

28 344

6310.81980.18022

03.0

96.1

n

Work Sampling Method-- Example --

Workgroup TotalObservation

ActivityObservation

Proportion ofTotal

ConfidenceLower

ConfidenceUpper

RequiredSample Size

RN

688 124 0,1802 0,1515 0,209 631

LVN

344 28 0,0814 0,0525 0,1103 320

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 Savings0.25[(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