Quote:What readability index did they use to determine it?  It seems like they used the Coleman-Liau Index or possibly SMOG.

Edit: Nevermind.  Read the report.  They used some sort of average.  Though their numbers look a little low in that case.  

Different indices will give you different grading levels.  And grade level doesn't really give you much on how 'intelligent' the lyrics are.

Examples:
Who Let The Dogs Out

Flesch-Kincaid Grade Level 10.7

Gunning-Fog Score 13.5

Coleman-Liau Index 4.8

SMOG Index 3.4

Automated Readability Index 11.6Harper Valley PTAFlesch-Kincaid Grade Level 4.2

Gunning-Fog Score 6.1

Coleman-Liau Index 6.7

SMOG Index 3.8

Automated Readability Index 3

Average Grade Level 4.8Hey You

Flesch-Kincaid Grade Level 3.1

Gunning-Fog Score 5.6

Coleman-Liau Index 5.7

SMOG Index 3.2

Automated Readability Index 2.3Never Ever Getting Back Together

Flesch-Kincaid Grade Level 6.3

Gunning-Fog Score 8.6

Coleman-Liau Index 6.3

SMOG Index 5.3

Automated Readability Index 4.8

Average Grade Level 6.3Bohemian Rhapsody

Flesch-Kincaid Grade Level 3.9

Gunning-Fog Score 6.1

Coleman-Liau Index 5.8

SMOG Index 5.3

Automated Readability Index 0.9Dark Horse

Flesch-Kincaid Grade Level 10

Gunning-Fog Score 12.8

Coleman-Liau Index 4.9

SMOG Index 5.1

Automated Readability Index 10.1Baby

Flesch-Kincaid Grade Level 9

Gunning-Fog Score 10.5

Coleman-Liau Index 5

SMOG Index 4.2

Automated Readability Index 7.4Happy Birthday

Flesch-Kincaid Grade Level 3.4

Gunning-Fog Score 5.7

Coleman-Liau Index 8.3

SMOG Index 4.1

Automated Readability Index 3.1All About that Bass

Flesch-Kincaid Grade Level 20.5

Gunning-Fog Score 23.5

Coleman-Liau Index 4.6

SMOG Index 6

Automated Readability Index 23.7Not Afraid

Flesch-Kincaid Grade Level 34.9

Gunning-Fog Score 38.1

Coleman-Liau Index 5

SMOG Index 9.9

Automated Readability Index 41.8