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Time study topics. What are they?What can you accomplish with them?What methods and equipment do you need?What do data sheets (for recording times) look like?How many observations do you need?How do you calculate allowances and standard times (ST)?. Time Studies. Time studies are: Observations
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1. Chapter 10: Time Studies IE 5511 Human Factors
Prof: Caroline Hayes
2. Time study topics What are they?
What can you accomplish with them?
What methods and equipment do you need?
What do data sheets (for recording times) look like?
How many observations do you need?
How do you calculate allowances and standard times (ST)?
3. Time Studies Time studies are:
Observations of work and the time it takes to perform it.
Method of determining a fair days work.
Frederick Taylor popularized times studies in the late 1800s. Founder of the modern time study.
Work is divided into elements which are timed.
4. Time Study Methods Time studies can be conducted with simply, low-cost equipment:
Stop watch (or other time recording devices: time study board, computer, etc.)
Video and/or audio tape,
Time study forms, and other written notes,
Time study often combined with motion study (e.g. additionally looks at how motions are made)
Early studies analyzed physical work, but many of the principles/methods apply equally well to analysis of cognitive work (e.g. using verbal protocol studies.)
5. Functions of Time Studies Establish work standards: e.g. recommended times in which tasks should be completed by qualified, trained operators, without excessive fatigue,
Set expectations which are fair to both employee and company.
Identify sources of error, difficulties, sub-optimal aspects,
Improve existing processes, tools, or work environments,
6. Functions of Work Standards Establish reasonable productivity targets for experienced workers,
Provide productivity goals for training purposes,
Eliminate waste,
Make processes more consistent,
Reduce variability, improve quality.
7. Establishing Work Standards Need to use work measurement procedures (e.g. time studies) to set accurate work standards.
Data must be specific to a particular
process,
work environment,
tool set and
operator population
Estimates that are not based on data may not be sufficiently accurate for setting standards which have a large impact on company and employees.
8. Preparing for a Time Study The steps in the process studied must already be standardized; e.g. sequences have been determined.
Operator must be fully qualified, trained, and acquainted with standardized process being studied.
Must inform supervisor, union steward, department head.
Make sure all materials are available for the process.
9. Time Study Procedure Select operator(s)
Break task down into elements (before you start study)
Observe operators performing task: record time taken for each element, over several cycles.
Assign appropriate allowances (e.g. allow time for necessary but non-productive activities, such as rest, cleaning eye-glasses, etc.
Determine appropriate work standards.
10. Selecting an Operator Get supervisor to help in identifying appropriate operators,
Ideally, you want someone qualified, trained and very familiar with process (may need to provide training before study) if your goal is to set standards.
Prefer an average or slightly above average operator.
Sometimes you have no choice of operator only one person is available who does the job.
11. Divide Task into Elements Work Element: a group of motions that is relevant to the experimenters study objectives.
(For cognitive work, divide verbal protocol into utterances roughly equivalent to a single thought.)
Watch for several cycles (before study starts) to identify useful work elements for the task.
Look for easily identifiable start and end signals, often auditory or visual. Examples:
The clink of a part being set on the fixture,
Setting a cup on the counter in front of the customer,
The moment when a customers hand touches the credit card as the cashier hands it back.
12. Divide task into elements (cont) This is not so easy to do!
Preparatory observations: Devote a half hour or so to observation of the task: start to identify relevant operations, and practice recording them.
Data sheets: Create a spread sheet or recording scheme to help you record elements quickly and easily.
Work element revisions: new elements may keep popping up over several days! You may also find that two or more elements should really be combined. Example: for cashiers, cleaning and organizing, chatting with co-workers are just different ways of waiting for customers.
Level of abstraction. The size of the divisions between elements depend on what you need to do in the analysis.
13. Record Significant Information Time Study Observation form provides space for:
Study date
Observer Name
Operator Name
Department,
Study Start Time
Study End Time
Also useful to record:
Machines
Jigs, fixtures
Working conditions
Sketch of work area layout
14. Positioning Observer Stand slightly behind operator, usually easier than sitting easier to follow movements of operator or get out of way).
Try not to distract or interfere with operator.
Avoid distracting conversation that may upset routines.
15. Divide Task into Elements Smallest unit that can be accurately timed is about 0.04 minutes (approx 2 to 3 sec).
Breakpoints: use sound and sight both to identify breakpoints between elements, (e.g. sound of a part clinking in finished bin, sound of a latch clicking shut, etc.)
16. Example Caribou coffee study: Corporate Goals Stated goals: To streamline operations so that employees will have more time to interact with the customers.
Additional benefits: customers will be happier if they do not have to wait as long.
17. Example Caribou coffee study: Analysts Goals To understand how long each activity took,
To identify what typical processes were,
To streamline processes, where possible,
To set work performance standards, and customer expectations,
How long should customers expect to wait for a cup of coffee?
How should performance of stores be assessed?
What performance goals should trainees aim for?
18. Identifying work elements It can take several hours or days of observation to identify all work elements and to come up with a consistent naming.
New elements may keep appearing, over time,
19. Two methods for recording element times Snapback method: after recording the end of an operations, snapback or reset the stopwatch to zero.
Advantages: dont need to compute element duration,
dont need to record delays or foreign elements.
Disadvantages: may loose some time during snapback
Continuous method: Start timer at zero at start of all observations, let it run continuously. Record elapsed time at element breakpoints.
Advantages: all time is recorded, operators and unions like that, makes method easy to sell,
Disadvantages: may take more computational effort
20. Data recording sheets You may need to devise data recording sheets that fit the study goals, the task and the type of data.
You may use the example data recording sheets in the book, but they are not meant to fit all situations,
Examples:
Recording a fixed sequence of operations.
Recording a variable sequence of operations,
Recording arrival and wait times in a line,
22. Examples of Data Recording Sheets: for recording operations that happen in an unpredictable order: custom assembly of one-off products
23. Examples of data recording sheets: for sampling length of time customers wait in a line
24. Other types of data
25. How many cycles should be observed? There are several ways of estimating the number of cycles that should be observed in order to obtain accurate standard:
The statistical method.
The General Electric (G.E.) method,
26. The Statistical Method Estimate numbers of observations required Goal: to limit the error in the estimate for the mean operation time (OT) to plus or minus a given percentage, k.
Equation to estimate n, no# of observations needed:
n = t s
k x
Problem: If you havent taken any observations yet, how can you know x and s ?
You cant. Must estimate them first with a small pilot study.
27. The Statistical Method Estimate numbers of observations required Goal: to limit the error in the estimate for the mean operation time (OT) to plus or minus a given percentage, k.
Equation to estimate n, no# of observations needed:
n = t s
k x
Problem: If you havent taken any observations yet, how can you know x and s ?
You cant. Must estimate them first with a small pilot study.
28. The Statistical Method Estimate numbers of observations required Goal: to limit the error in the estimate for the mean operation time (OT) to plus or minus a given percentage, k.
Equation to estimate n, no# of observations needed:
n = t s
k x
Problem: If you havent taken any observations yet, how can you know x and s ?
You cant. Must estimate them first with a small pilot study.
29. The Statistical Method Estimate numbers of observations required Procedure: it takes two steps to calculate sample size:
Pilot study: Take small set of observations or use historical data to estimate the parameters:
Mean OT: xp (mean operation time observed in the pilot study), use xp as an estimate of x for the full scale study
Sample standard deviation, s.
Full scale study. Use these parameters to calculate sample size of a larger study.
30. Example Estimation of number of Observations Pilot study: you take n = 25 readings for an element. You get 25 readings, x1 through x25: 0.28, 0.24, 0.33, 0.33, etc.
When you summarize your data, you find:
xp = S xi /25 = 0.30, where xp is the average time required
to perform the work element.
s = S (xi xp)2 = [(.28-.30) + (.24-.30) + ]2 = 0.09
v n 1 v 25 1
Use s = 0.09 from the pilot study to estimate s for the larger study.
31. Example Estimation of number of Observations Pilot study: you take n = 25 readings for an element. You get 25 readings, x1 through x25: 0.28, 0.24, 0.33, 0.33, etc.
When you summarize your data, you find:
xp = S xi /25 = 0.30, where xp is the average time required
to perform the work element.
s = S (xi xp)2 = [(.28-.30) + (.24-.30) + ]2 = 0.09
v n 1 v 25 1
Use s = 0.09 from the pilot study to estimate s for the larger study.
32. Example Estimation of number of Observations Pilot study: you take n = 25 readings for an element. You get 25 readings, x1 through x25: 0.28, 0.24, 0.33, 0.33, etc.
When you summarize your data, you find:
xp = S xi /25 = 0.30, where xp is the average time required
s = S (xi xp)2 = [(.28-.30) + (.24-.30) + ]2 = 0.09
v n 1 v 25 1
Use s = 0.09 from the pilot study to estimate s for the larger study.
33. Example Estimation of number of Observations Pilot study: you take n = 25 readings for an element. You get 25 readings, x1 through x25: 0.28, 0.24, 0.33, 0.33, etc.
When you summarize your data, you find:
xp = S xi /25 = 0.30, where xp is the average time required
s = S (xi xp)2 = (.28-.30)2 + (.24-.30)2 + = 0.09
v n 1 v 25 1
Use s = 0.09 and xp from the pilot study to estimates to jump start the calculation for the larger study.
34. Example (continued) Estimation of number of Observations Full scale study: how many observations of an element do you need to take in a larger time study, in order be 95% confident that your measurement of x is within k = 5% of the true value?
k = 5% (acceptable error)
a = 1 confidence level = 1 - .95 = .05
From pilot study we estimated: xp = S xi = 0.30, s =0.09
Now you need to look up t. You can look up t if you know a and the degrees of freedom (d.o.f):
d.o.f. = np - 1 = 25 1 = 24
n = t s = 2.064 x 0.09 = 153.3 observations
k x 0.05 x 0.30 (round up to integer)
35. Example (continued) Estimation of number of Observations Full scale study: how many observations of an element do you need to take in a larger time study, in order be 95% confident that your measurement of x is within k = 5% of the true value?
k = 5% (acceptable error)
a = 1 confidence level = 1 - .95 = .05
From pilot study we estimated: xp = S xi = 0.30, s =0.09
Now you need to look up t. You can look up t if you know a and the degrees of freedom (d.o.f):
d.o.f. = np - 1 = 25 1 = 24
n = t s = 2.064 x 0.09 = 153.3 observations
k x 0.05 x 0.30 (round up to integer)
36. Example (continued) Estimation of number of Observations Full scale study: how many observations of an element do you need to take in a larger time study, in order be 95% confident that your measurement of x is within k = 5% of the true value?
k = 5% (acceptable error)
a = 1 confidence level = 1 - .95 = .05
From pilot study we estimated: xp = S xi = 0.30, s =0.09
Now you need to look up t. You can look up t if you know a and the degrees of freedom (d.o.f):
d.o.f. = np - 1 = 25 1 = 24
n = t s = 2.064 x 0.09 = 153.3 observations
k x 0.05 x 0.30 (round up to integer)
37. The t-distribution (pg. 701) Look up t-value in the table (or use the Excel function)
38. The t-distribution (pg. 701)
39. Example (continued) Estimation of number of Observations Full scale study: how many observations of an element do you need to take in a larger time study, in order be 95% confident that your measurement of x is within k = 5% of the true value?
k = 5% (acceptable error)
a = 1 confidence level = 1 - .95 = .05
From pilot study we estimated: xp = S xi = 0.30, s =0.09
Now you need to look up t. You can look up t if you know a and the degrees of freedom (d.o.f):
d.o.f. = np - 1 = 25 1 = 24. From table: t = 2.064
n = t s = 2.064 x 0.09 = 153.3 observations
k x 0.05 x 0.30 (round up to integer)
40. The General Electric (G.E.) Method Assumes more error in smaller measurements not much attention to typical variability in the operation itself)
41. Using the data from our in-class pilot study Task: collating & stapling 3 sheets of paper
Operations:
Assemble sheets 1, 2, 3
Hand-off/Align/Staple
Can you the data from our in-class pilot study to estimate no# observations needed to insure that we are:
95% confident (a = 0.05) that our answer is within:
10% error (k=.10)
43. Calculate n, sample size needed for operation 1 xp = 5.0
s = 0.71
k = 0.10 (10% error); Let alpha = 0.05
n = t s 2 = ? *0.71 2
k xp .10 * 5.0
What value should we use for t?
44. Calculate n, sample size needed for operation 1 xp = 5.0
s = 0.71
k = 0.10 (10% error); Let alpha = 0.05
n = t s 2 = 2.776 * 0.71 2 = 15.4 obs.
k xp 0.10 * 5.0
What if we decrease k to 5% ?
45. Calculate n, sample size needed for operation 1 xp = 5.0
s = 0.71
k = 0.05 (5% error)
n = t s 2 = 2.776 * 0.71 2 = 62.7 obs.
k xp 0.05 * 5.0
The no# of observations greatly increases!
46. Foreign Elements A foreign element is one that does not explicitly belong in the sequence
Typically one subtracts them from observations (when possible) to get a more true time.
Examples:
Worker has to adjust glasses,
Must speak to supervisor,
Rest break, lunch break,
Equipment search: must find new wrench.
47. Foreign Elements Some foreign elements can be eliminated,
But others cannot or should not be:
Foreign elements can an idea of how much extra time (e.g. allowances) is reasonable to allow in an operation.
48. Allowances Allowances refers to extra time allowed, beyond completion of the task itself
Some allowances are necessary for health and long term efficiency (like rest breaks),
Others are pragmatically necessary, (like time for picking up dropped tools or consulting with supervisor)
49. Computing Standard Times A standard time is a combination of:
The time it takes to complete a task
Allowances.
This approach recognizes that it is not possible to work at top efficiency all day, all the time.
50. Methods for computing standard times Method 1: Add in allowances: compute required rest.
ST = NT + NT x allowance
= NT (1 + allowance)
Method 2: Compute allowances as a % of task time.
ST = NT / (1 allowance)
51. Example: Method 1 Suppose that your time study shows that it takes 3.5 minutes on average to complete a task. Rule of thumb for manual tasks: 15% allowances.
ST = NT + (NT * allowance)
= 3.5 min + (3.5 min * .15)
= 3.5 min + 0.525 min
= 4.03 minutes.
Experienced operators will be expected to complete the task in this time.
52. But how can you estimate allowances? Observe foreign elements what percentage of total time do they comprise?
Chapter 11 outlines many additional methods for calculating allowances:
For personal needs,
For fatigue reduction
53. Next, identify possible sources of fatigue Abnormal posture,
Muscular force,
Ventilation,
Lighting,
Visual strain
Mental strain,
Etc.
(see check list, Table 11 2).
54. Question: Does it make sense to estimate:
Allowances
Standard time
Efficiency
for a cashier who may spend much time waiting for customers to arrive?
55. How should Standard Times be used to Evaluate and Motivate People? What happens when you set up a reward system?
All jobs have same standard time, but some are more difficult,
Busy-time often results in slower production because you are exceeding capacity,
Do you always get the behavior you expect?
56. Time Sheet Operation Start time End time Total time
Average:
