Consider the daily simple returns of Johnson & Johnson stock from January 1998 to December 2008. The data are in the file d-jnj9808.txt or can be obtained from CRSP. Convert the returns into log returns in percentage.

(a) Build a GJR model for the log return series. Write down the fitted model. Is the leverage effect significant at the \(1 \%\) level?

(b) Build a general threshold volatility model for the \(\log\) return series.

(c) Compare the two TGARCH models.