Three Months Ended Six Months Ended
June 30, June 30,
2013 2012 2013 2012
Income before income taxes
$ 5,779 $ 7,186Income tax expense 950 2,271 1,802 2,861 Net income $ 1,785 $ 3,334 $ 3,977 $ 4,325
Diluted income per common share
Diluted weighted-average common shares outstanding 27,369 27,177 27,456 27,362 Income before income taxes decreased 51% and 20% for the three and six months ended
June 30, 2013, respectively, as compared to the three and six months ended June 30, 2012, respectively. The decrease in income before income taxes for the three and six months ended June 30, 2013was primarily due to an increase in general, administrative, and marketing expenses, partially offset by an increase in product revenues, which increased margins, as discussed above. The Company's effective income tax rate was approximately 35% and 31% for the three and six months ended June 30, 2013, respectively, as compared to 41% and 40% for the three and six months ended June 30, 2012, respectively. The Company's income tax rate for the six months ended June 30, 2013was favorably impacted by the full year 2012 research and development tax credit, which was enacted in January 2013and, therefore, reduced the Company's tax expense during the first quarter of 2013. The Company's income tax rate in 2012 was negatively impacted by the absence of a research and development tax credit, which was not enacted for the 2012 tax year during 2012. Net income and diluted income per common share decreased for the three and six months ended June 30, 2013as compared to the three and six months ended June 30, 2012, primarily due to the decrease in income before income taxes, as discussed above. Diluted income per common share could be unfavorably impacted in future periods by the issuance of additional shares of common stock and favorably impacted by the Company's repurchase of its common stock. Stock repurchases are impacted by many factors, including: stock price, available funds, and competing demands for such funds, and as a result, may be suspended or discontinued at any time.
The Company believes the demand for BioGlue is seasonal, with a decline in demand generally occurring in the third quarter followed by stronger demand in the fourth quarter. Management believes that this trend for BioGlue may be due to the summer holiday season in
Europeand in the U.S. The Company'smarket for BioGlue in Japanis still in a growth phase, however, the Company believes that demand for BioGlue in Japanmay continue to be lowest in the second quarter of each year due to the slower summer holiday season in Japan.