The economy constantly goes through periods of boom and bust business cycles. Managers of newly minted Pring Turner Business Cycle ETF (DBIZ) watch these cycles to take advantage of the best investing opportunities in each stage of these cycles. Tom Kopas is CEO of Pring Turner Capital Group, based in Walnut Creek, Calif., and co-manager of the ETF, which launched in December. He also co-wrote "Investing in the Second Lost Decade," published by