Although there are other methods, intellectual development today is most often expressed by the intelligence quotient (IQ). The article briefly explains the history of the use of five different intelligence quotients in both Croatian and global psychological theory and practice. In addition to the two classical IQ measures, Stern’s as a decimal and Terman’s as an integer, which were calculated as the ratio between mental (MA) and chronological (CA) age, three deviation quotients have also been developed. The first was introduced by David Wechsler in 1939 with an arithmetic mean of M=100 and a standard deviation (SD) of 15 units. Raymond Cattell proposed a second solution in 1951, with M=100 and SD of 24 units. Finally, Maud Merrill developed a third form in 1960 with M=100 and SD of 16 units. In Croatia, it is documented that the “decimal” quotient remained in use until the mid-1980s. The EFPA Board of Assessment in the Test Review Model 2025 advocates for using only IQ with a SD of 15 units. Since it will take time for this to be accepted as a single standard and given the current diversity of IQ values, it is necessary to continue to indicate the corresponding standard deviation along with the IQ.

classical or ratio IQ, Stern’s IQ, Terman’s IQ, deviation IQ, Wechsler’s IQ, Cattell’s IQ, Maud Merril’s IQ, the history of IQ in Croatia