It is not possible to guarantee a sufficient large power for all values of formula_32 as formula_31 may be very close to 0. The minimum (infimum) value of the power is equal to the confidence level of the test, formula_34 in this example 0.05 . However, it is of no importance to distinguish between formula_35 and small positive values. If it is desirable to have enough power, say at least 0.90, to detect values of formula_36 the required sample size can be calculated approximately: