Erin and Kate are studying depression in older adults. Using the Beck Depression Inventory II, Erin finds that patients in hospice care are more depressed than those who live at home. However, when Kate repeated this study using the Hamilton Rating Scale for Depression she did not find a difference in depression scores between those in hospice care and those who lived at home. What threat to validity may explain the difference in their results?

Possible answers:

interaction of the causal relationship with settings

experimenter bias

treatment diffusion

interaction of the causal relationship with outcomes