== Computing dprimes and betas == Dprimes and Betas may be computed in SPSS using the probit function. The UCLA statistics department give [[http://www.linguistics.ucla.edu/faciliti/facilities/statistics/dprime.htm|further details.]] They suggest values upto 2 are typical dprime values. A table showing dprime values for true positives and false alarm combinations [[FAQ/sigdet/effecttab| is available.]] *Also available by typing sigdet at a UNIX prompt *Excel syntax available [[http://psy.ucsd.edu/~kang/sdt/sdt.htm|here]]. [CUT AND PASTE SPSS SYNTAX BELOW INTO A SYNTAX WINDOW AMENDING DATA AS REQUIRED] {{{ * Computes Dprimes and Betas for signal detection theory * amend data input as required SET FORMAT F10.5. DATA LIST FREE / HI FN FP CN. BEGIN DATA 9 1 3 7 6 4 2 8 END DATA. IF (HI EQ 0) HI = 0.5. IF (FN EQ 0) FN = 0.5. IF (FP EQ 0) FP = 0.5. IF (CN EQ 0) CN = 0.5. COMPUTE HIP = HI / (HI + FN). COMPUTE FPP = FP / (FP + CN). COMPUTE DP = PROBIT(HIP) - PROBIT(FPP). COMPUTE BETA = EXP(-0.5*(PROBIT(HIP)**(2))) / EXP(-0.5*(PROBIT(FPP)**(2))). LIST VARIABLES= DP BETA HI FN FP CN. }}} * Multiple invocations of the macro in the same interactive session will produce the following note: >The macro name specified on the DEFINE command duplicates the name of a previously defined macro. This instance will take precedence. This warning does not indicate a problem and may be ignored.