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 … ISE 311

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. ISE 311

Random and Constant Errors ISE 311

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. ISE 311

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. ISE 311

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. ISE 311

Developing the Standard Plan the work. Classify the data. Group the elements. Analyze the job. Develop the standard. ISE 311

Curve Fitting To analyze experimental data: Plot the data. Guess several approximate curve shapes. Use a computer to determine the constants for the shapes. Select which equation you want to use. ISE 311

Statistical Concepts Least-squares equation Standard error Coefficient of variation Coefficient of determination Coefficient of correlation Residual ISE 311

Curve Shapes Y independent of X Y = A Determine that Y is independent of X by looking at the SE. ISE 311

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 ISE 311

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 ISE 311

Straight Lines ISE 311

Geometric Curves ISE 311

Exponential Curves ISE 311

Hyperbolas ISE 311

Parabolas or Hyperbolas with a Third Constant ISE 311

Curve Shapes Y depends on X, multiple variables Y = A + BX + CZ Results in a family of curves ISE 311

Example Application: Walk Normal Times (min) .0553 .1105 .1654 .2205 .0590 .1170 .1751 .0550 .1660 .2090 .0521 .1045 .1680 .2200 .0541 .1080 .1625 .2080 .0595 .1200 .1800 .1980 ISE 311

First, plot the data ISE 311

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? r2 = .986 σ = .0073 t =.0054 + .01d ISE 311

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 ISE 311