AS DESCRIBED in chapter 1, I define an “important” institutional change as one that historians or congressional specialists perceive to have had substantial effects on congressional operations. I operationalize this definition by counting a change as important if five sources each suggest that the institutional change in question had such effects. While reading each source, I recorded all cases of institutional change during the four periods that affected rules and procedures, the committee system, and leadership instruments. I generated a list of changes from each source and then compared the lists.
One issue is what constitutes a single change. This is not a problem for rules changes, which are discrete events. But alterations in leadership instruments and the committee system may result from an accumulation of numerous smaller steps. For example, the development of centralized Senate leadership under William Allison (R-Iowa) and Nelson Aldrich (R-R.I.) resulted from a series of decisions over the course of several years. One could consider each individual step in this process to be a single institutional change and apply the criteria listed above to each of these steps. However, this forces an emphasis on singular events that obscures the potential for institutional change to occur gradually. As a result, I treat a set of related changes as a single case if at least five scholars treat the individual changes as related parts of a single, common change that the scholars identify in specific terms and judge to be important.
I relied on approximately thirty sources for case selection in each period. I sought to use a wide variety of sources, which approach the topic of congressional politics from diverse vantage points. 1 The sources are listed in table A. 1.
Since fewer histories are available for the 1970–89 period, I supplemented the sources listed by using the article entitled “Inside Congress” in each edition of Congress and the Nation, which is published every four years by Congressional Quarterly. Since the “Inside Congress” article typically aims to cover congressional changes comprehensively, I used only the