in measurement is about consistency. If a measure is reliable, it means that if the same measure is applied consistently to the same person, the result will be the same each time
Ie) have you ever had a problem with alcohol in your life? (Not reliable bc change in relationship with alcohol over life)
\-if measures are unreliable, they cannot be trusted to detect patterns and relationships
\- common issue: memory
Ie) how many wine, beer, and liquor drinks have you consumed each day for the last 3 months? (quantitative)- not gonna remember exacts
\-observation data issues= may miss some parts of interaction you observe, observations vary based on things like time and are not very reliable