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Perancangan Eksperimen [1] February 8, 2009

Posted by desrinda in Perancangan Eksperimen.
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Masa perkuliahan di semester kedua diawali dengan kelas Perancangan Eksperimen (DoE, Design of Experiment), diajar oleh Ibu Ir.Isti Surjandari, MT, MA, PhD. Menurut silabus, melalui kuliah ini pesertanya diharapkan akan mampu mengorganisir pengumpulan, pengolahan, dan penganalisaan data dengan baik & benar secara statistik maupun engineering (rekayasa) dalam melakukan rancangan percobaan yang bertujuan untuk pengambilan keputusan.

Textbook: Design and Analysis of Experiments, Douglas C. Montgomery, John Wiley & Sons, 2005.

BASIC PRINCIPLES

Principle of parsimony (statistics) = The scientific principle that things are usually connected in the simplest or most economical way.

KISS = Keep It Statistically Simple, or “Keep it simple, Stupid!”

Any process can be modelled into simple flow chart:

doe-1

X = controllable factors, anything that affect output
Y = uncontrollable factors, should be blocked (can’t be eliminated)

Outputs should be measurable, i.e.
– Quantity of received customer’s complaints (service industry)
– Quantity of rejected item (manufacturing)
– Food taste (in scale from 1 to 5)
– etc.

Point of departure must be set by defining hypothesis to be tested.
Ho = No relationship between controllable factors and outputs
Ha = There is relationship between controllable factors and outputs

Purpose of analysis are vary: For understanding, explanation, prediction, or control. In general, to decide which factors can increase efficiency.

The strategy of experiments:
– Best guess
– One-Factor-at-A-Time (OFAT)
– Statistically designed experiments = DoE, taking summaries of result of interaction between factors

doe-2

Dr. Leonard Lye taught DoE (STAT-EASE, Statistics Made Easy) using DoE golfer as sample. The software was Minitab.

Based on Fisher’s factorial design:
– 2 factors, 2 level each = 2 x 2 = 4 runs
– 3 factors, 2 level each = 2 x 2 x 2 = 8 runs
– and so on
If not all of run is taken into experiment, then it’s called fractional factorial design.

Steps:
1. Statement of problem (e.g. using fishbone diagram)
2. Design of experiment (method, hypothesis, etc.)
3. Analysis

Six Sigma: DMAIC = Define, Measure, Analysis, Improve, Control.

Statistical DoE Principles:

doe-3

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