By: Julia and Krista

iTunes Song Lengths

Background

• Pop– Softer alternative to

rock and roll aimed at youth market

– Began in 1920s– Revolutionized by TV

• MTV• Madonna and Michael

Jackson

Background

• Rock– Blend of black

rhythm-and-blues with white country-and-western

– Originated in late 1940s and early 1950s• United States and

Great Britain• Elvis and the Beatles

Background

• Country– originally found in

the Southern United States and the Appalachian Mountains• Blend of different

styles of music found in these regions

– Began to evolve in the 1920s• Vernon Dalhart

Background

• R&B (Rhythm and Blues)– Originated in 1940s– Term originally used

to describe recordings marketed to urban African Americans

– Louis Jordan

Background

• Hip-Hop– Contains stylistic

elements like rapping, DJing, sampling, scratching and beatboxing

– Originated in South Bronx in New York in 1970s

– DJ Kool Herc• “Godfather” of hip-

hop

Topic and Procedure• Comparing song

length to genre and artist gender– Genres: Pop, Rock,

Country, R&B, Hip-hop

• Data from i tunes– First 30 non-repeating

artists in each genre– Recorded length, genre

and, artist gender

• Put song length in decimal form

Boxplots of Genre vs. Song Length

Genre vs. Song Length Analysis

• Country– Shape

• Slightly left skewed

– Center• Median 3.45 mins

– Spread:• Minimum: 2.583 mins• Maximum: 4.35 mins• No apparent outliers

• Hip-HopShape Slightly right skewed

CenterMedian 3.925 mins

Spread:Minimum: 2.95 minsMaximum: 5.567 minsNo apparent outliers

Genre vs. Song Length Analysis

• Pop– Shape

• Roughly symmetric

– Center• Median 3.684 mins

– Spread:• Minimum: 3.017 mins• Maximum: 4.817 mins• No apparent outliers

• R&BShapeSymmetric

CenterMedian 4.083 mins

Spread:Minimum: 2.433 minsMaximum: 5.533 minsApparent outliers at minimum

and maximum

Genre vs. Song Length Analysis

• Rock– Shape

• Roughly symmetric

– Center• Median 4.017 mins

– Spread:• Minimum: 3.2 mins• Maximum: 5.967 mins• Apparent outliers at

max, 5.933 mins, and 5.917 mins

• Conclusion• Country songs

generally shortest• Rock songs generally

longest• Pop, hip-hop, and R&B,

fall in the middle

Assumptions for 1-Sample T-test

• State1. SRS2. Normal population

or n 30

• Check1.Not SRS but best

sample so we proceeded with test

2. n=30 30

1-Sample T-test for Pop Songs

•We reject the Ho because p-value <

•We have sufficient evidence that the true average length of a pop song is greater than 3.5 minutes.

0044.0)29/806.2(

806.2

5.3:

5.3:

dftPns

xt

Ha

Ho

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1-Sample T-Interval for Pop Song Lengths

We are 99% confident that the mean length of a pop song is between 3.2526 and 3.7474 minutes.

Histograms of Song Length vs. Artist Gender

Song Length vs. Artist Gender Analysis

• Male– Slightly right skewed with center at about 4.4 minutes

• Female– Slightly right skewed with center at about 4.2 minutes

• Both – Uniform with center at approximately 4 minutes

• Conclusion– More male artists than female and mix of both genders– Least amount of mix of both gendered groups – Males had longest song lengths and both groups had

shortest song lengths

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• Check1.Not SRS but best

sample so we proceeded with test

• n=30 30

Assumptions for 1-Sample T-Test

• State1. SRS2. Normal population

or n 30

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1-Sample T-Test for Male Artist Song Lengths

0001.0)115/152.8(

152.8

4.4:

4.4:

dftPns

xt

Ha

Ho

•We reject the Ho because p value <

•We have sufficient evidence that the true average length of a song by a male artist is less than 4.4 minutes.

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1-Sample T-Interval for Male Artist Song Lengths

)0172.4,7715.3()(* nstx

We are 95% confident that the mean length of a song by a male artist is between 3.7715 and 4.0172 minutes.

Bar Chart of Genre vs. Artist Gender

Genre vs. Artist Gender Analysis

• Country had most amount of mixed gender groups, rock had the least with 0

• Rock was only genre with all male artists

• Pop had greatest amount of female artists– Followed by R&B

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• Check1. Not SRS but best

sample so we proceeded with test

2. 30(0.25)=7.5 1030(0.75)=22.5 10 did not pass but we

proceeded with test

3. population 300

1-Proportion Z-Test Assumptions

• State1. SRS

2. np 10

n(1-p) 10

3. Population 10*n

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1-Proportion Z-Test for Female R&B Artists

npp

pp

)1(

ˆ

Ho: p=.25

Ha: p <.25

Z= = -0.634

P(z<-0.634)=0.2635

•We fail to reject the Ho because p-value >

•We have sufficient evidence that the true percent of female R&B artists is equal to 25%.

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1-Proportion Z-Interval for Female R&B Artists

)35848.0,04152.0()ˆ1(ˆ

*ˆ

n

ppzp

We are 97% confident that the true percent of female R&B artists is between 4.152% and 35.848%.

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Application• Population is pop, rock, hip-hop, R&B, and

country songs• We were able to compare the lengths of

songs to each genre as well as the gender of the artist. We were also able to compare the gender of the artist to the each genre– Useful when searching for songs or burning CD’s

• We discovered that most songs are between 3.5 and 4.5 minutes

• Songs by male artists tended to be the longest

• All genres had more male than female artists

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Bias/Error

• Sample could have been better– SRS– Larger size– Repeating artists in different genres

• Only used i-tunes• Rounded for song lengths in decimal

form• Rounded for null hypotheses

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Conclusions• We thought that pop songs would be

shortest and rock songs would be longest– Country had smallest average song length– R&B had largest average song length

• We expected the length of songs by male artists to be shortest and the length of songs by bands of both artists to be longest– Males actually had highest mean song length

and bands of both had the smallest mean song length

Conclusions• We expected pop songs to be by mostly female

artists, hip-hop songs to be by males, and country and R&B songs to be by bands consisting of both– About half of pop was by females– Hip-hop, country, R&B, and rock were mostly by males– Few total song were by band with both genders

• We found that pop songs are between about 3.25 and 3.75 minutes

• The length of songs by male artists are between about 3.77 and 4.02 minutes

• Percentage of female R&B artists is between 4.1% and 35.8%

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