Random irrelevancies in the intervention setting. Any random changes in the setting of the intervention, including location, climate, time, and so on, may affect scores on the outcome measure and make...

Random irrelevancies in the intervention setting. Any random changes in the setting of the intervention, including location, climate, time, and so on, may affect scores on the outcome measure and make an effective intervention appear ineffective. Example: Because the agency was being refurbished, David was forced to change offices several times during the course of his intervention with the Trask family. These changes made the intervention appear less effective than before the disruptions.