Why is 'internal consistency' a measure of reliability? It looks like a measure of validity instead.
Definitions:
"Internal consistency reflects the extent to which items within an instrument measure various aspects of the same characteristic or construct." (Revicki, 2014)
"Reliability refers to the extent to which a measure yields the same number or score each time it is administered, all other things being equal" (Hays & Revicki, 2005)
Example:
Let's assume I've made a survey A in which all items measure level of physical activity.
First item: I love sport
Second item: I hate sedentary lifestyle
Survey A has high internal consistency.
Let's assume I've made a survey B in which all items measure level of physical activity.
First item: I love sport
Second item: I hate sushi
Survey B has low internal consistency. Hating sushi is a poor measure of physical activity. Therefore, it's the construct validity issue. Reliability, as defined by Hayes & Revicki, won't suffer, because we will expect similar results from similar people.
