dˈaɪəmənd ænd vˈæn tˈæsəl fˈaʊnd ðætðə dˈɪfɹəns bᵻtwˌiːn ðɪ ɪmplˈaɪd "ɹˈɪsk fɹˈiː" ɹˈeɪt θɹuː bˈɑːks spɹˈɛdz ænd tɹˈɛʒɚɹiz, ɔːɹ sˈɪmɪlɚɹ ɪnvˈɛstmənts ɪn ˈʌðɚ kˈʌntɹiz sˈɛntɹəl bˈæŋks, ɪz ˈeɪ "kənvˈiːnɪəns jˈiːld" fɚðɪ ˈiːz ʌv ɪnvˈɛstmənt ɪnðə sˈɛntɹəl bˈæŋks sᵻkjˈʊɹɹᵻɾiz.
Diamond and van Tassel found that the difference between the implied "risk free" rate through box spreads and Treasuries, or similar investments in other countries' central banks, is a "convenience yield" for the ease of investment in the central bank's securities.