Rudolf Urbschat (1997). "Tendencies in the German Newspaper and Magazine Press Since 1945". Communications. The European Journal of Communication Research. 22 (3): 351. doi:10.1515/comm.1997.22.3.343. S2CID145590766.
Ulrich Kaiser (2002). "Optimal Cover Prices and the Effects of Website Provision on Advertising and Magazine Demand". ZEW Discussion Paper (2–54). doi:10.2139/ssrn.339140. hdl:10419/24590. S2CID167310.
Ulrich Kaiser (2002). "Optimal Cover Prices and the Effects of Website Provision on Advertising and Magazine Demand". ZEW Discussion Paper (2–54). doi:10.2139/ssrn.339140. hdl:10419/24590. S2CID167310.
Rudolf Urbschat (1997). "Tendencies in the German Newspaper and Magazine Press Since 1945". Communications. The European Journal of Communication Research. 22 (3): 351. doi:10.1515/comm.1997.22.3.343. S2CID145590766.
Ulrich Kaiser (2002). "Optimal Cover Prices and the Effects of Website Provision on Advertising and Magazine Demand". ZEW Discussion Paper (2–54). doi:10.2139/ssrn.339140. hdl:10419/24590. S2CID167310.