Editing Cronbach's alpha (section)

===Cost to obtain a high level of reliability===
Nunnally's idea was that there is a cost to increasing reliability, so there is no need to try to obtain maximum reliability in every situation.

====Trade-off with validity====
Measurements with perfect reliability lack validity.<ref name = ChoKim/> For example, a person who takes the test with a reliability of one will either receive a perfect score or a zero score, because if they answer one item correctly or incorrectly, they will answer all other items in the same manner. The phenomenon where validity is sacrificed to increase reliability is known as the attenuation paradox.<ref>{{cite journal|first=J.|last=Loevinger|title=The attenuation paradox in test theory|journal=Psychological Bulletin|volume=51|issue=5|pages=493–504|date=1954|doi=10.1002/j.2333-8504.1954.tb00485.x|pmid=13204488}}</ref><ref>{{cite journal|first=L.|last=Humphreys|title=The normal curve and the attenuation paradox in test theory|journal=Psychological Bulletin|volume=53|issue=6|pages=472–6|date=1956|doi=10.1037/h0041091|pmid=13370692}}</ref>

A high value of reliability can conflict with content validity. To achieve high content validity, each item should comprehensively represent the content to be measured. However, a strategy of repeatedly measuring essentially the same question in different ways is often used solely to increase reliability.<ref>{{cite journal|first=G. J.|last=Boyle|title=Does item homogeneity indicate internal consistency or item redundancy in psychometric scales?|journal=Personality and Individual Differences|volume=12|issue=3|pages=291–4|date=1991|doi=10.1016/0191-8869(91)90115-R}}</ref><ref>{{cite journal|first=D. L.|last=Streiner|title=Starting at the beginning: An introduction to coefficient alpha and internal consistency|journal=Journal of Personality Assessment|volume=80|issue=1|pages=99–103|date=2003|doi=10.1207/S15327752JPA8001_18|pmid=12584072|s2cid=3679277}}</ref>

====Trade-off with efficiency====
When the other conditions are equal, reliability increases as the number of items increases. However, the increase in the number of items hinders the efficiency of measurements.