ABSTRACT
Every investigation with more than two conditions faces two linked hazards: escalation of false alarms and loss of power. Each comparison of two means is an opportunity for false alarm. Four conditions yield six two-mean comparisons—six opportunities for false alarms. Hence the effective α for this family of six comparisons is greater than the α used for each single test—not .05 but .20. This familywise α escalates rapidly with more conditions.
