Frank B. Cross & James F. Spriggs Ii, the Most Important (and Best) Supreme Court Opinions and Justices

• Jurisdiction: United States,Federal
• Publication year: 2010
• Citation: Vol. 60 No. 2

THE MOST IMPORTANT (AND BEST) SUPREME COURT OPINIONS AND JUSTICES

Frank B. Cross^*

James F. Spriggs II^**

INTRODUCTION .............................................................................................. 409

I. CRITERIA FOR IDENTIFYING THE MOST IMPORTANT SUPREME

COURT OPINIONS ................................................................................ 412

A. Citation Measures for Important Cases ..................................... 415

B. Validity of Citation Use .............................................................. 420

II. QUANTIFYING THE MOST IMPORTANT SUPREME COURT DECISIONS .. 430

A. Data ............................................................................................ 430

B. Leading Cases by Different Metrics ........................................... 431

C. Change in Importance over Time ............................................... 442

D. Overrated and Underrated Opinions ......................................... 446

III. DETERMINANTS OF AN OPINION'S LEGAL IMPORTANCE .................... 449

A. Case Characteristics .................................................................. 450

1. Issue Area of Opinion ........................................................... 451

2. Legal Area of Opinion .......................................................... 453

3. Legal Complexity .................................................................. 455

B. Age of Opinion ............................................................................ 456

C. Ideological Factors .................................................................... 457

1. Ideological Direction of Decision ........................................ 460

2. Ideological Composition of Court Coalitions ...................... 462

3. Ideological Distance from Citing Court ............................... 463

D. Opinion Characteristics ............................................................. 464

1. Nature of Majority Coalition ................................................ 465

2. Citations in Opinion ............................................................. 467

3. Length of Opinion ................................................................. 469

4. Footnote Ratio of Opinion .................................................... 472

E. Additional Controls .................................................................... 474

F. Result .......................................................................................... 475

1. Case Characteristics ............................................................ 478

2. Age ........................................................................................ 478

3. Ideological Factors .............................................................. 479

4. Opinion Characteristics ....................................................... 479

5. Controls ................................................................................ 481

G. Substantive Import ...................................................................... 482

IV. INDIVIDUAL JUSTICES ......................................................................... 486

V. ARE THESE THE BEST CASES IN THE SUPREME COURT'S HISTORY? ... 498

CONCLUSION .................................................................................................. 500

INTRODUCTION

Identifying the most important cases decided by the Supreme Court is more than an interesting parlor game; the process illuminates the function of the law. The Court issues scores of opinions annually, some of which go on to assume great importance in future years, while many others languish in desuetude. Some opinions may appear to be important (e.g., they are commonly found in constitutional law casebooks), when in fact they have little real impact on the nation's law. For purposes of this Article, we define importance in legal terms-opinions with greater legal importance are more relevant for deciding legal disputes and thus helping to structure legal outcomes.

The identification of key cases has practical significance for judicial research. When researchers study Supreme Court cases empirically, they commonly treat each case as an equally important data point. In reality, though, one single Supreme Court decision may be vastly more significant than numerous other small cases.¹There is reason to believe that the dynamics of decision making in especially salient cases may be different than for cases of lesser practical significance.²The "lack of a valid, well-accepted, and

'ready' measure of salience" has resulted in significant "voids in our knowledge" of Supreme Court decisions.³

We enter this void with a study of the citations to past Supreme Court opinions. Citation analysis is "growing mainly because it enables rigorous quantitative analysis of elusive but important social phenomena," including stare decisis.⁴Considerable quantitative research has been done on the outcomes of Supreme Court decisions, but the content of opinions has not been much studied. This is a serious limitation because it is the opinion-not the mere outcome-that is the Court's salient product.⁵Past research "focused too narrowly on the disposition of the case."⁶Studies of case outcomes without consideration of opinion content can lead to very misleading conclusions.⁷

This Article studies one aspect of opinion content to determine which opinions are most important, and seeks to ascertain why they are so important.

Identifying the most important opinions and the determinants of such importance has considerable legal significance. If the ideology of the Justices drives opinion importance, that fact has implications for decisions about the composition of the Court. If some feature of the opinion itself drives importance, that fact is crucial to our evaluation of the Justices, or Court norms and procedures. Perhaps a larger majority makes an opinion more important. Perhaps the use of more citations in an opinion gives it greater future impact. Perhaps some Justices are simply better at writing opinions of significance. Ascertaining such determinants is central to the evaluation of the Court and its members.

This Article embarks upon the project of identifying which Supreme Court opinions have proved the most legally significant and exploring why. We employ an analysis of citations to opinions. Other legal authors have used citation studies to assess the importance or value of opinions or judges.⁸We build upon these existing analyses with more sophisticated measures and a focus on what makes Supreme Court opinions more or less important in the law.

The first Part of the Article sets out our criteria for identifying the most important Supreme Court opinions: the frequency of citation by subsequent judges and Justices. Citations are a facially clear measure of the importance of opinions, at least within the law itself. They are commonly used in research and offer an available measure for quantitative analysis. Like any empirical proxy used to represent a concept of interest, the use of citations to study discrete aspects of law is imperfect, but the primary criticisms of their use, such as the "settled law" phenomenon, do not invalidate the measure.⁹Our analyses, for example, show that our measures of case importance correspond to perceptions of case importance.

In the second Part, we quantify the most important Supreme Court opinions. We identify the opinions with the most citations at the Supreme Court, circuit court, and district court levels. This produces very different lists, revealing different dimensions of importance depending on the level of the judiciary. We also provide an additional list for the Supreme Court using a more sophisticated measure of importance available from analysis of the full network of citations at the Court. This enables us to identify the most overrated and underrated opinions of the Court.

Having various measures at different levels of the judiciary to assess importance, the third Part of this Article analyzes what makes an opinion more or less important. We analyze the role of characteristics of the case itself, the age of the precedent, the role of ideological factors, various opinion characteristics, and control variables. Through multiple regression analysis, we discover that all these characteristics are relevant for understanding importance, though particular results are not always as expected according to prevailing theories. Features of the opinion itself that appear to matter include, for instance, its length and the number of citations it contains.

The fourth Part examines the associations of opinion importance and the Justice who authored the opinion. With the ability to control for specific case characteristics from the preceding Part, we examine whether opinions authored by different Justices have greater future citation power, whether at the Supreme Court or lower court levels. Our analysis shows that a few Justices appear to author particularly influential opinions.

The fifth and final Part assesses whether the importance of the Supreme Court's opinion, significant in itself, may also be considered a measure for the best opinions. While the notion of the "best" opinion is inevitably a subjective one, our quantitative empirical analysis provides a reasonable guide for opinion quality. While no study can provide conclusive answers in itself, we provide the first quantitative analysis of opinion importance and quality, upon which we hope others will build.

I. CRITERIA FOR IDENTIFYING THE MOST IMPORTANT SUPREME COURT

OPINIONS

Some efforts have been made to identify the most important opinions of the Supreme Court. The Oxford Guide to Supreme Court Decisions summarizes those considered to be the most important (the "Oxford list").¹⁰Congressional Quarterly publishes a Guide to the U.S. Supreme Court that lists cases it considers to be of landmark status.¹¹These rankings of case importance are based on the...