Differentiate between reliability types: internal consistency and test-retest.

• A. Internal consistency measures test length; test-retest measures questions' difficulty.
• B. Internal consistency assesses consistency among items in a test; test-retest assesses score stability over time.
• C. Internal consistency is about teacher reliability; test-retest is about student effort.
• D. Internal consistency is not a reliability concept; test-retest is the only valid measure.

Answer: (B)

Reliability types focus on how consistently a measurement works. Internal consistency looks at how well the items on a test work together, essentially whether all the questions are measuring the same underlying construct. When items hang together well, people's answers tend to move in a coordinated way, which shows up as high correlations among items (Cronbach’s alpha is a common way to quantify this).

Test-retest reliability, on the other hand, examines stability over time. If you give the same test to the same people on two different occasions and the scores are similar, that indicates the test yields consistent results across time, assuming the construct hasn’t changed.

So, internal consistency is about coherence among the test items, while test-retest is about score stability across time. The other statements mix up what reliability indexes actually measure (length, difficulty, teacher or student factors), or deny the role of internal consistency as a reliability concept.