Question

which of the following is a threat to external validity?
a. maturation
b. multiple - treatment interface
c. experimental mortality
d. history

Explanation:

To determine the threat to external validity, we analyze each option:

• Option A (Maturation): Threat to internal validity (changes due to time/person's growth), not external.
• Option B (Multiple - treatment interface): Occurs when multiple treatments affect results, threatening external validity as the effect may not generalize to single - treatment contexts.
• Option C (Experimental mortality): Threat to internal validity (participant dropout affecting results), not external.
• Option D (History): Threat to internal validity (external events during study affecting results), not external.

Answer:

B. Multiple - treatment interface