Chapter 10: Time Studies

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Chapter 10 Time Studies

• IE 5511 Human Factors
• Prof Caroline Hayes

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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)?

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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.

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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.)

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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,

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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Positioning Observer

• Stand slightly behind operator, dont sit
  easier to follow movements of operator or get our
  of way).
• Try not to distract or interfere with operator.
• Avoid distracting conversation that may upset
  routines.

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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.)

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Coffee study 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?

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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,

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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

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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,

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Recording a fixed sequence of operations
Repeated cycles of the sequence
Foreign Elements
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Examples of Data Recording Sheetsfor recording
operations that happen in an unpredictable order
custom assembly of one-off products
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Examples of data recording sheets for sampling
length of time customers wait in a line
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Other types of data
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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,

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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.

2
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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.

2
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.

2
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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.

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ExampleEstimation 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.

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ExampleEstimation 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.

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ExampleEstimation 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.

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ExampleEstimation 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 and xp from the pilot study to
  estimates to jump start the calculation for the
  larger study.

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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)

2
2
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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)

2
2
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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)

2
2
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The t-distribution (pg. 701)Look up t-value in
the table (or use the Excel function)
Alpha, a
Degrees of freedom, d.o.f.
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The t-distribution (pg. 701)
Alpha 0.05
Alpha, a
Degrees of freedom, d.o.f.
t 2.064
d.o.f 24
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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)

2
2
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The General Electric (G.E.) Method Assumes more
error in smaller measurements not much
attention to typical variability in the operation
itself)
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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.

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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.

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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)

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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.

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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)

ST Standard Time the time in which you expect
workers to complete an operation. NT Normal
Time time required to complete an operation for
a given operator OT Mean Observed Time to
complete an operation (from time study).
For an experienced operator who works at a 100
rate (R), OT NT, and NT OT x R/100
where R the performance rating of the
operator.
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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.

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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

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Next, identify possible sources of fatigue

• Abnormal posture,
• Muscular force,
• Ventilation,
• Lighting,
• Visual strain
• Mental strain,
• Etc.
• (see check list, Table 11 2).

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Question

• Does it make sense to estimate
• Allowances
• Standard time
• Efficiency
• for a cashier who may spend much time waiting for
  customers to arrive?

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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?

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Class Exercise

• Perform task
• Do a pilot study of 4 observations
• Calculate how many observations for a full scale
  study, a 0.5, k .20
• Pretend that your 4 observations ARE your full
  scale study.
• Calculate ST using Method 1.
• Let allowances 15

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Time Sheet
Date
Study start time

• Operation Start time End time
  Total time
• Average