Which type of data (cross-sectional or time series) is each variable?
a. Value of Standard & Poor’s 500 stock price index at the close of each trading day last year.
b. Closing price of each of the 500 stocks in the S&P 500 index on the last trading day this week.
c. Dividends per share paid by General Electric common stock for the last 20 quarters.
d. Latest price/earnings ratios of 10 stocks in Bob’s retirement portfolio.