lp, excel, and merit – oh my! (w/apologies to frank baum)

LP, Excel, and Merit – Oh My! (w/apologies to Frank Baum)

CIT Research/Teaching Seminar Series (Oct 4, 2007)

John Seydel

No, It’s Not About Getting Back to Kansas!

Here’s the ProblemDeveloping merit evaluations of multiple faculty members

Some are good all around Each is good at something Which “somethings” should be considered more/less

important? How much more/less important?

Why not borrow from Economics: concept of Pareto efficiency?

Identify the efficient set of faculty members Avoid answering the “importance” question

We can use LP (linear programming) with some help from Excel to address thisHence: “LP, Excel, and Merit”

What’s LP?Consider a production planning problem Liva’s Lumber (refer to handout)

3 products 3 constraints 1 objective (maximize weekly profit)

Summary table:

Modelling: LP model and Excel model

Product: CDX AC Form  

How much:  ???  ???  ???  

Profit: $ 5.00 $ 7.00 $ 6.00 Available

Cutting: 2 3 10 54,000

Gluing: 4 7 4 24,000

Finishing; 2 3 7 18,000

Now, the Merit Problem

Typical merit criteria: Teaching Research Service

Consider the teaching criterion Our CoB evaluations have 35 dimensions

associated with the teaching criterion What do we do with all those

There are too many to weight So we just average them; i.e., we treat them as if

they’re all equally important! “Follows syllabus” is important as “explains clearly”

Let’s consider a smaller example (Table 1)

Aggregation of Results

Humans want a single performance measuresTypical schemes Simple average (see Table 2) Focus on “overall effectiveness” question

(e.g., #8) Also, weighted average

Weights determined by whom (committee, administrator, statute, . . . )?

Illustrated by MBO So, what’s wrong with a simple average?

Obscures individual strengths and weaknesses Artificially values minor differences

DEA to the Rescue (?)

We want to evaluate the outcomes of behaviors (decisions) on the basis of Multiple criteria to be considered for the

outcomes No generally acceptable set of weights exists

(and no one is willing to determine such)

This is where DEA (data envelopment analysis) can be usefulConsider each instructor to be a DMU (decision-making unit)Apply the concept of economic efficiency . . .

Efficient Set ConceptSet of entities (DMUs) where no entity performs as well or better on all criteria Graphically: convex hull Consider concept from finance: efficient

portfolio Risk Return

Any entity’s weighted multicriteria score will be the same as the others’ scores, if they all get to choose their own weights These entities are called efficient decision making unitsConsider a simple example (subset from Table 2) . . .

Bicriterion Performance Comparision

  Criterion   Simple Avg Weighted Avg

Instrtuctor Impartial Prepared   Value Rank Value Rank

OBA 4.77 3.78   4.28 1 4.08 2

GJB 3.02 2.83   2.93 6 2.89 5

IAB 2.01 2.20   2.11 7 2.14 7

OVB 3.39 4.24   3.82 3 3.99 3

BFH 3.74 2.35   3.05 5 2.77 6

DEI 2.68 3.58   3.13 4 3.31 4

OLK 4.58 3.96   4.27 2 4.15 1

Weight: 0.30 0.70          

Graphically Identifying the Efficient Frontier

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 1.00 2.00 3.00 4.00 5.00

Preparedness

Imp

arti

alit

yy

OBA

OLK

OVBBFH

IAB

GJBDEI

Some Basic Definitions

Efficiency = Output / InputMaximum possible efficiency is defined as 100% (i.e., 1.00)Output for an instructor is her/his weighted average evaluation scoreInput for all instructors is theoretically the same (100% of time available)This leads to a model (recall the LP model for Liva’s Lumber) . . .

Efficiency ModelChoose a set of criterion weights for a given instructor so as to

Maximize: Instructor’s Output/Input Subject to:

Each other instructor’s Output/Input <= 1 Weight values are positive

Which is the same as Maximize: Instructor’s Weighted Average Score Subject to:

Each other instructor’s Weighted Average Score <= 1 Weight values are positive

Since each instructor’s input is defined to be 1.00Note, however, that the “weighted average” is now scaled to the 0.00 – 1.00 interval

An Example DEA Output Model for Evaluating Faculty Teaching

Let w1 and w2 be the weights to assign to impartiality and preparedness, respectivelyThen, for instructor GJB (for example, the objective is to

    Maximize:   3.02w1 +  2.83w2   (GJB score) 

    ST:            4.77w1 +  3.78w2 ≤ 1.00     (OBA)                        3.02w1 +  2.83w2 ≤ 1.00     (GGB)                        2.01w1 +  2.20w2 ≤ 1.00     (IAB)  . . . 4.58w1 +  3.96w2 ≤ 1.00     (IAB) w1, w2 > 0.00We can use Excel to model and solve this, but we need to reformulate and solve for every instructorThat’s where macro programming comes in . . .

Now, Let’s Apply This to the Data

Consider the model for QVAThen note the summary tableThings of interest Size of efficient set Rank reversals Comparison with simple average

approach (Figure 1)

Where To From Here?

Constraining the weightsRanking the “efficient” instructorsExpand across other criteria in the merit evaluationsOther DEA applications (decsion support) Comparing ecommerce platforms Vendor selection Other . . . ?

Go looking for more “Lions and tigers and bears (oh my)!”

Appendix

The LP Model for Liva’s Lumber

We can model this mathematically:    Let         x1 = number of sheets of CDX to produce weekly         x2 = number of sheets of form plywood to produce weekly        x3 = number of sheets of AC to produce weekly

The objective is to

    Maximize:   5x1 +  7x2 +   6x3                  (Weekly profit) 

    ST:            2x1 +  3x2 + 10x3 ≤ 54000     (Cutting)                        4x1 +  7x2 +  4x3  ≤ 24000     (Gluing)                        2x1 +  3x2 +  7x3  ≤ 36000     (Finishing) Solving is “simply” a matter of determining the best combination of x1, x2, and x3

Enter Excel

Create a spreadsheet table like the summary tableAdd a few formulae

Total profit Total amount of each resource consumed

Solve by trial and error . . . ?Better: use the Solver tool

Find the optimal solution quickly Tinker with parameters and re-solve

Even better: use Solver with a macro button Record macro Call subroutine when editing onClick event for button

Table 1:Example Evaluation Items

Table 2:Example Departmental Summary

DEA Model for Instructor QVL

Results Across Instructors

Figure 1: DEA vs. Simple Averaging