W. . Rahayu and W. . Hariyanto, “Analysis of Portfolio Expected Returns as a Material Consideration for Investors in Choosing Investments in the Pandemic Period (Formation of Optimal Portfolios Using the Black Litterman Model on Hang Seng Stocks for the 2017-2019 Period): Analisis Penilaian Expected Return Portofolio Sebagai Bahan Pertimbangan Investor dalam Memilih Investasi di Masa Pandemi (Pembentukan Portofolio Optimal Dengan Model Black Litterman pada Saham Hang Seng Periode 2017-2019)”, acopen, vol. 5, p. 10.21070/acopen.5.2021.2149, Dec. 2021.