The phrase "trained observers" refers to people who have been taught and have practice in watching and noticing things accurately. They are skilled at paying attention and noticing important details. Full definition
Because of the cost and prestige factors, in its early days such instruments were generally used by trained observers. (wattsupwiththat.com)
Remember that the modest gain in reliability with virtually no improvement in predictive power took hours of training observers of whom a large portion had to be dismissed. (jaypgreene.com)
Our services include training observers, implementing a common language of instruction, and building the capacity of teachers to use research - based instructional strategies to improve student learning. (marzanoevaluation.com)