Jackson scale started with a lot and narrowed it down. Can never truly know the true score but we found out anyway. Reliability is the proportion of the variance in observed scores as accounted for by true scores. We have the variance of the obtained scores, and we have the variance of the true score. Of the observed variable (differences we see among people) . 52% of those are due to real differences between them and 48% is due to random error. Gave the observed score and the error score. Use the second version of the equation, but have to figure out the true score. Add extra column and calculate the true score. Obtained score error score = true score (unless it"s an opposite) Now that we have the true scores we do the same thing as before. True score variance divided by true score variance = 1. 1 the error score divided by the obtained score.