MEAGERMEAGERMEAGERMEAGER

Microsoft ExcelMicrosoft ExcelAutomated GraderAutomated Grader

Applications of MEAGER

• Microsoft Excel courses

• Microsoft Office Apps courses

Purposes

• To reduce the time and effort required in grading assignments

• To grade assignments more accurately and in greater detail compared to hand grading via hard copy

What does MEAGER grade?

• Text labels• Numbers • Formulas• Worksheet names

• Fonts– Face– Size– Style (B/I/U)– Color

What does MEAGER grade? (continued)

• Cell– Alignment (L/R/C)– Fill Color– Indent level– Orientation (tilt)– Number format

• Currency, Percent• Accounting,

Scientific• Etc.

• Borders– Color– Style

• solid broken

– Thickness

• Row Height• Column Width• Merged Ranges

What does MEAGER not grade?

• Charts

• Embedded objects– Pictures– Clip Art– Org charts– Word Art

• Drawing objects– Shapes– Lines– Drop shadows

• Controls– Buttons– List Box– Text Box, etc.

How does MEAGER work?

• MEAGER is a Microsoft Access application

• Attributes are extracted – from Excel workbooks – into Microsoft Access tables:

_Cell _Format _Border _Formula _Row _Col

_Worksheet

Example Workbook

Cell TableWorksheet

Row

Col

Value NumberFormatFontName

FontSize

FontStyle

Seven-Year Plan

1 1 E-Book.com General Book Antiqua

26 Bold

Seven-Year Plan

2 1 Seven-Year Projected Financial Statement

General Book Antiqua

16 Bold

Seven-Year Plan

3 2 2001 General Arial 10 Bold Italic

Seven-Year Plan

4 2 131201647 #,##0_);(#,##0) Arial 10 Bold

Format Table

Worksheet Row Col FType FValue

Seven-Year Plan 2 8 Fill Color Orange

Seven-Year Plan 2 8 Font Color White

Seven-Year Plan 3 2 Alignment Center

Seven-Year Plan 3 2 Orientation 45

Formula Table

Worksheet Row Col Formula

Seven-Year Plan 2 8 =NOW()

Seven-Year Plan 4 2 =B20*(B21/(1-B24))

Seven-Year Plan 4 3 =B4*(1+$B$22)*(1-$B$23)

Seven-Year Plan 13 2 =SUM(B8:B12)

How does MEAGER work? (continued)

• After attributes are extracted from both– instructor’s correct workbook – a student’s workbook

• and placed into tables

• The resulting tables are compared– missing attributes are detected– unequal attributes are found

Marking Errors

• Errors are recorded in an Access tableAND

• Student worksheets are marked– Strike-through format is added to incorrect values

and formulas– Comments are added to cells to describe errors

Example Correct Workbook

Student’s Marked Up Version

ScreenshotsScreenshotsScreenshotsScreenshots

Grade Report

Class Errors Report

Grading Challenges Grading Challenges Grading Challenges Grading Challenges

Corner Sums: An Error?– Assignment instructs bottom right (F8) value

to be sum of column F: =Sum(F3:F7)

– What if student makes F8 the sum of row 8?=Sum(B8:E8)

– Is the answer incorrect?

Corner Sums: An Error? (cont’d)

Note both column F and row 8 are totalsThe sum of column F and row 8 are both equivalent to

=Sum(B3:E7)

=Sum(F3:F7) and =Sum(B8:E8) are not identical, but ARE algebraically equivalent

Similar Equivalent Formulas

• =B9+(10%*B9)

• =SUM(G3:G8)G3 is =3.2% * E3G8 is =3.2% * E9

• =B9*(1+10%)

• =3.2%*E9E9 is =SUM(E3:E8)

Correct Student

Algebraic Simplification Needed

Order of Operations:

f(g(x)) vs g(f(x))

Sum of Products vs Product of Sums

Symbolic CAS(Computer Algebra System)

• Interpreter for symbolic manipulation of mathematical expressions (like Maple but free)

http://www.mb.hs-wismar.de/Mitarbeiter/Pawletta/00Uwe/casE.html

• Accepts identifiers consisting of at least one letter followed by several letters or digits. – All Cell refs from A1 to IV65536 are valid identifiers

• Evaluates functions with same syntax as Excel: SQRT(x),EXP(x),LN(x),SIN(x),COS(x),TAN(x),ASIN(x),

ACOS(x),ATAN(x),SINH(x),COSH(x),ABS(x)

Includes function: Simplify(instr, outstr)

Symbolic CAS(Computer Algebra System)

Shortcomings for Excel formulas

• Does not handle recognize ranges

• Does not recognize many Excel functions, including common ones: Sum & Average

• Does not recognize Excel function symbolslike $ and %

Algorithm to Detect Equivalent Formulas

Given student’s formula SF and correct formula CF

For both formulas: Do Until no replacement SF or CF

Replace Sum/Average functions in SF or CF with +, / opsFor Each cell reference in SF and CF If the cell reference contains another formula Replace cell reference with nested formula

LoopRemove $, percents (shift two decimals), remaining ranges

in CF,SFCreate string to be evaluated: CF || “-(“ || SF || “)”Use Simplify function to determine if result is zero

Challenge #2

Renaming Worksheets

• Problem:– Assignment has multiple worksheets

– Assignment requires three sheets to be renamed: Payroll, AP, AR

– Student does not rename sheets, leaving nonempty sheets: Sheet1, Sheet2, Sheet3

– How does one match worksheets?

Renaming Worksheets

• Possible solutions to matching worksheets– Match by highest percent of matching cell

values• Expensive: every pair of worksheets must be

compared

– Match based on worksheet statistics• Match closest count of nonempty: constants,

formulas, etc.

– Match based on ordinal position

Renaming Worksheets

• MEAGER solution– Match based on worksheet statistics

• Match closest count of nonempty cells (constants and formulas)

– When multiple worksheets have same number of nonempty cells, no rename is performed

How to use MEAGERHow to use MEAGERHow to use MEAGERHow to use MEAGER

Before Using MEAGER• (The hard part) Instructor must gather all

student Excel files

• Files need to have unique names so they can be placed in the same folder

• Copy the student folder for possible grading again– The files are marked up (comments are added,

scores are added at the bottom of the worksheet)

• Correct file should be in a different folder than student file directory

Selecting Files

• User must select the correct worksheet– click on browse file button (or type filename)– navigate to file– select correct excel file

• Next select ANY student file – Use browse button or type filename

Points to Deduct

• 100 point grading scale• Enter number of points to be deducted for

errors– Mistyped/missing labels or numeric constants– Incorrect formulas– Formatting errors

Workbook Grading Rules

• Extraneous values and formats ARE NOT deducted by default

• The same amount is deducted for all types of formatting errors.

• Formats applied to ranges (fill color, borders) are deducted for each cell in the range.

• An incorrect number format applied to a large range would be deducted at each cell

Options: Visible Marking– Displays the Excel window as documents

are being graded– When cells are extracted, nothing changes– When grading comments are added and

error cells are stricken– User can jump between MEAGER and Excel

windows

Options: Skip Format Grading

– Only grades formulas and cell labels/number– Useful with first class assignments– Avoids grading more advanced features

(for example, row height/col width) before being covered in class

– Avoids “error overload”; hides details that might be more easily handled manually

Options: Deduct Extraneous

• To count any extra formatting or cells values against the student

• If student enters name, class, date information, these will marked as incorrect (correct this manually in student grade)

Error Analysis

– Helps discover possible plagiarism

– Considers a pair of students at a time– How many errors do they have in common?

• More errors, more evidence of plagiarism

– What percent of a student A’s errors were also made by student B?

Student Pairs Common Errors

Total Errs (for first file)