Supreme Court RulingsData Science Project by Matthew Girard

Winter 2017

� The database of all supreme court decisions from 1946-2016 was compiled by Professor Spaeth of Washington University Law and covers 200+ variables for each decision and a database codebook

� This dataset was shared on Kaggle earlier this year (Jan 2017) and I wanted to explore the data for more questions and some Rstudioexperience

Context

Description of the dataset

� Dataset contains information on 8,737 Supreme Court decisions between 1946-2016

� Data includes the following for each decision:� Chief Justice who presided the court at the time of the decision� Whether the decision was ‘liberal’ or ‘conservative’� Whether the decision was reached after oral arguments� Whether the decision overturned a prior legal precedent� Number of Majority and Minority votes for the decision� Number of other columns (e.g., lower court that issued prior ruling)

� Overall – the raw data was of moderate quality. For the purpose of my analysis, I excluded a small number of data points that were logically inconsistent (e.g., ‘# of minority votes’ > ‘# of majority votes)

Questions explored:

� Question 1: Over the last 70 years has the supreme court become more polarized / partisan?

� Challenge: hard to quantify / measure degree of polarization or partisanship; data unclean (e.g., majority votes < minority votes)

� Approach: using Rstudio, check for the share of ‘liberal vs. conservative’ decisions and ‘number of split majority vs. supermajority vs. unanimous’ decisions under different Chief Justices

� Question 2: Are there fundamental differences between cases where the ruling is “split majority” vs. “unanimous” decisions?

� Approach: classified the decisions by the type of ruling: split majority, super majority and unanimous and plotted variables like whether the decision was liberal / conservative, whether oral arguments were used and whether the decision overturned a prior legal precedent

Level of polarization in Supreme Court decisions – by size of majority votes, 1946-2016

‘46 – ‘53

Polarized: in these situations a number of other justices

disagreed with the decision / reasoning

Conclusion:Overall, the current court

(under Jus. Roberts) has fewestshare of polarizing decisions

and most unanimous decisions

Not polarized: in these situations all justices agreed with the decision / reasoning

‘53 – ‘69 ‘69– ‘86 ‘86 – ‘05 ‘05 – ’16**present Chief JusticeVariable: chief_justice

Level of polarization in Supreme Court decisions – by decision ideology, 1946-2016

Conclusion:Overall, the current court

(under Jus. Roberts) has close to an even split on decisions

that can be regarded as conservative or liberal^

Influenced by high number of liberal justices appointed by Presidents F.D.R and Truman

(12 in total)

*present Chief Justice^definitions based on a detailed list of guidelines used by the raw file

Conservative^Liberal^

‘46 – ‘53‘53 – ‘69 ‘69– ‘86 ‘86 – ‘05 ‘05 – ’16*

Variable: chief_justice

Level of polarization by decision ideology, 1946-2016

Conclusion:Overall, the decision ideology does not seem to strongly correspond to

the degree of polarization; but there is some weak relationship

More than 2/3rd agreed

^definitions based on a detailed list of guidelines used by the raw file

Conservative^Liberal^

Less than 2/3rd

agreed All agreed

Variable: split

Level of polarization by legal precedent treatment, 1946-2016

Conclusion:Overall legal precedents were overturned only in a very small number of cases. Within this small set, there is more likelihood that the court is split (thin

majority) than unanimously agreed when overturning the precedent

More than 2/3rd agreed

^definitions based on a detailed list of guidelines used by the raw file

No impact on legal precedents^Legal precedent overturned^

Less than 2/3rd

agreed All agreed

Variable: split