Pradeep Chhibber and Geetha Murali, "Duvergerian Dynamics in the Indian States: Federalism and the Number of Parties in the State Assembly Elections," Party Politics, 12 (January, 2006), 5-34.

First Paragraph:
Duverger's law predicts that two parties will capture all the votes in districtlevel elections in countries with single-member, simple-plurality rules. Research has shown that, at its heart, Duverger's law relies on the assumption that district-level elections are characterized by strategic voting. Following a standard definition of 'strategic voting' - that voters prefer not to waste their votes if meaningful and potentially consequential votes can be cast - the implication of such an assumption in single-member, simple-plurality elections is that voters prefer to vote for a candidate who has a chance of winning the election, all else being equal.

Figures and Tables:
Figure 1. Effective number of parties in the state assembly elections in India
Table 1. The effect of party type and national influence on the effective number of parties at the district level
Table 2. The effect of party type and national influence on the SF ratio at the district level
Figure 3a. The appropriateness of N (the difference between the vote share of the winner and first loser and the vote share of the second loser [third-placed party]
Figure 3b. Vote share trends for the top three effective parties
Figure 4a. Distribution of effective number of parties in Tamil Nadu
Figure 4b. Distribution of effective number of parties in Tamil Nadu
Figure 4c. Distribution of SF ratios in Tamil Nadu
Figure 5a. Distribution of effective number of parties in Bihar
Figure 5b. Distribution of effective number of parties in Uttar Pradesh
Figure 6a. Distribution of SF ratios in Bihar
Figure 6b. Distribution of SF ratios in Uttar Pradesh
Figure 7. Effective number of parties in Andhra Pradesh
Appendix A. State assembly elections included in analysis dataset
Appendix B. Histograms of effective number of parties and SF ratios
Appendix C. Histograms of the effective number of parties by state
Appendix D. Histograms of SF ratios by state

Last Paragraph:
In this article, we have shown that Duverger's law holds for state assembly elections in India, but there are clear violations of the law. We argued that these violations are more likely to occur in states where more than two national parties or a combination of national and regional parties are competing for votes. Given that in the Indian federal system the national and state governments can exercise some authority in districts, voters may vote for national or regional parties even if those parties are not likely winners in the district. Is this analysis more generally valid? Future research on federal systems like Canada, where Duverger's law is also violated, would provide leverage on developing a more comprehensive answer. In addition, an in-depth analysis of Bihar and Uttar Pradesh may point to the interaction between current ethnic politics and federalism and further expose the socio-economic conditions under which Duverger's law breaks down at the district level.