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Chapter 30: Standard Data

Reusing previously determined times to predict standard times for new operations. E.g., predict cost of automotive repairs

Can be specialized for a particular industry, company, or process …

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Advantages of Using Standard Data Cost

Time study is expensive. Standard data allows you to use a table or an

equation. Ahead of Production

The operation does not have to be observed. Allows estimates to be made for bids, method

decisions, and scheduling. Consistency

Values come from a bigger database. Random errors tend to cancel over many studies. Consistency is more important than accuracy.

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Random and Constant Errors

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Disadvantages of Standard Data

Imagining the Task The analyst must be very familiar with the task. Analysts may forget rarely done elements.

Database Cost Developing the database costs money. There are training and maintenance costs.

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Motions vs. Elements

Decision is about level of detail. MTM times are at motion level. An element system has a collection of individual

motions. Elements can come from an analysis, time

studies, curve fitting, or a combination.

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Constant vs. Variable

Each element can be considered either constant or variable.

Constant elements either occur or don’t occur. Constant elements tend to have large random

error. Variable elements depend on specifics of the

situation. Variable elements have smaller random error.

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Developing the Standard

Plan the work. Classify the data. Group the elements. Analyze the job. Develop the standard.

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Curve Fitting

To analyze experimental data:1. Plot the data.

2. Guess several approximate curve shapes.

3. Use a computer to determine the constants for the shapes.

4. Select which equation you want to use.

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Statistical Concepts

Least-squares equation Standard error Coefficient of variation Coefficient of determination Coefficient of correlation Residual

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Curve Shapes

Y independent of X Y = A Determine that Y is independent of X by looking

at the SE.

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Y Independent of X If Y is not related to X (is independent of X), then Y=A, where

A is constant.

0 2 4 6 8 10

10

8

6

4

2

[x]

[y]y=4

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Curve Shapes

Y depends on X, 1 variable Y = A + BX Y = AXB

Y = AeBX

Y = A + BXn

Y = X / (A + BX) Y = A + BX + CX2

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Straight Lines

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Geometric Curves

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Exponential Curves

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Hyperbolas

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Parabolas or Hyperbolas with a Third Constant

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Curve Shapes

Y depends on X, multiple variables Y = A + BX + CZ Results in a family of curves

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Example Application: Walk Normal Times (min)

5 m 10 m 15 m 20 m

.0553 .1105 .1654 .2205

.0590 .1170 .1751 .2205

.0550 .1105 .1660 .2090

.0521 .1045 .1680 .2200

.0541 .1080 .1625 .2080

.0595 .1200 .1800 .1980

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First, plot the data

Time vs Distance

0

0.05

0.1

0.15

0.2

0.25

0 5 10 15 20 25

Distance, m

Tim

e, m

in.

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Equations for Walking NOTE: see attached Excel sheet

intercept = ______ slope = _________

r2 = _______ σ = __________

Therefore, Walk time is computed as:

t = __________________

So, if a new task is added that requires walking 7.4 m, how long should be allowed in the standard?

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Equations for Walk Data Set

Walk time h = –.13 + .11 (loge Distance, m)

r2 = .966 σ = .012 h

1/Walk time h = .24 – .96 (1/Distance, m)

r2 = .881 σ = .021 h-1