DECISION THEORY INTRODUCTION


 

Introduction

       It is a statistical tool or technique which is used to select the best way of doing any work.

       It helps in taking the best decision by subtracting (avoiding/skipping) useless alternative.

 

 

Types of Decision Problems

  1. Decision making under certainty.
  2. Decision making under uncertainty.
  3. Decision making under risk/conflict.

 

NOTE: IT IS ALSO KNOWN AS DECISION MAKING ENVIRONMENT.

 

 

 

METHODS

 



 

 

STEPS IN DECISION MAKING

  1. Determine various approaches or strategies.
  2. To know the effect of decision.
  3. To determine pay off.
  4. Construction of pay off table.

 

States of nature (event)

Alternatives (or payoff)

E1

A1

A2

A3

…..

E2

….

Laplace criterion

 

The following matrix gives the pay off of different strategies (alternatives) S1,S2,S3 and S4 against conditions (events) N1,N2,N3 and N4.

SELECT BEST ALTERNATIVE

N1

N2

N3

N4

S1

1000

1500

750

0

S2

250

2000

3750

3000

S3

-500

1250

3000

4750

S4

-1250

500

2250

4000

 

 

EXPECTED PAY OFF = 

       = no. of events

Let P1, P2, ….., Pn represent the pay off value  of each and every alternative

Calculation of expected pay

EXPECTED PAY OFF = 

now for the 1st strategy S1,

                                                   = 812.5

For S2,

                                                   = 2250

Expected Pay off

Select maximum of the expected pay off

 

812.5

2250

2125

1375

 

 

2250 is the maximum value of the expected pay off which means 2nd alternative will be best alternative.

If in the given question will give cost not pay off then minimum of them will be the best alternative for that case S1 would be the best alternative.

That’s how decision is taken under Laplace criterion.

 

 

OPTIMISM CRITERION

 

A). MAXIMAX CRITERION    (applicable for pay off matrix)

N1

N2

N3

N4

S1

1000

1500

750

0

S2

250

2000

3750

3000

S3

-500

1250

3000

4750

S4

-1250

500

2250

4000

 

 

 


Maximum pay off

Select maximum of the pay off

 
1500

3750

4750

4000

 

Here 4750 is maximum so S3 is the best alternative

 

 

 

B). MINIMIN CRITERION  (applicable for cost matrix)

N1

N2

N3

N4

S1

1000

1500

750

0

S2

250

2000

3750

3000

S3

-500

1250

3000

4750

S4

-1250

500

2250

4000

 


Minimum cost

Select minimum of the cost

 
0

250

-500

-1250

 

Here -1250 is minimum so S4 is the best alternative

 

 

PESSIMISM CRITERION

A). MAXIMIN CRITERION  (applicable for pay off matrix)

N1

N2

N3

N4

S1

1000

1500

750

0

S2

250

2000

3750

3000

S3

-500

1250

3000

4750

S4

-1250

500

2250

4000

 

 


Minimum pay off

Select maximum of the pay off

 
0

250

-500

-1250

 

Here 250 is maximum so S2 is the best alternative

 

 

B). MINIMAX CRITERION    (applicable for cost matrix)

N1

N2

N3

N4

S1

1000

1500

750

0

S2

250

2000

3750

3000

S3

-500

1250

3000

4750

S4

-1250

500

2250

4000

 

 

 


Minimum cost

Select minimum of the cost

 
1500

3750

4750

4000

 

 

 

Here 1500 is minimum so S1 is the best alternative

 

 

 

Question 1.

Pay off table

Strategies

States of nature

N1

N2

N3

S1

7,00,000

3,00,000

1,50,000

S2

5,00,000

4,50,000

0

S3

3,00,000

3,00,000

3,00,000

 

 

Which strategies should we choose on the basis of:

a). Maximin Criterion

B). Maximax Criterion

C). Laplace Criterion

 

 

A). Maximin criterion

Strategies

States of nature

N1

N2

N3

S1

7,00,000

3,00,000

1,50,000

S2

5,00,000

4,50,000

0

S3

3,00,000

3,00,000

3,00,000

 


 


Minimum Pay off

1,50,000

0

3,00,000

 

 


Here 3,00,000 is maximum so S3 is the best alternative

 

 

 

B). Maximax Criterion

Strategies

States of nature

N1

N2

N3

S1

7,00,000

3,00,000

1,50,000

S2

5,00,000

4,50,000

0

S3

3,00,000

3,00,000

3,00,000

 


 


Select maximum of the pay off

 
Maximum  Pay off

7,00,000

5,00,000

3,00,000

 

Here 7,00,000 is maximum so S1 is the best alternative

 

 

c). Laplace Criterion

Strategies

States of nature

N1

N2

N3

S1

7,00,000

3,00,000

1,50,000

S2

5,00,000

4,50,000

0

S3

3,00,000

3,00,000

3,00,000

 

 

EXPECTED PAY OFF = 

For S1,       = 3,83,333.33

For S2,       = 3,16,666.67

For S3,       = 3,00,000


 


Expected Pay off

3,83,333.33

3,16,666.67

3,00,000

 

 

Here 3,83,333.33 is maximum expected pay off so S1 is the best alternative

 

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