Universal ratios among correction-to-scaling amplitudes and effective critical exponents

Writing thermodynamic quantities near a critical point as fiAi|t|-i(1+ai|t|), where t=(T-Tc)Tc, we show that to leading order in =4-d one has aiaj=(i-i0)(j-j0), where i0 is the mean-field value of i. This ratio is also equal to (i, eff-i)(j, eff-j), where i, eff is derived from a fit of data with fi|t|-i, eff. Various experiments are analyzed and compared to these predictions.