Quiz. Do random errors accumulate? Name 2 ways to minimize the effect of random error in your data set. Validity. In our last class, we began to discuss some of the ways in which we can assess the quality of our measurements.
Note: Each measurement is 2 points higher than the true value of 10. The errors do no average out.
Note: Even when random error is present, E averages to 0 but S does not. Thus, we have reliable measures that have validity problems.
Note: Method 1 systematically overestimates T whereas Method 2 systematically underestimates T. In combination, however, those systematic errors cancel out.
In this example, we have someone with relatively high self-esteem, but this person systematically rates questions one point higher than he or she should.
If we “reverse key” half of the items, the bias averages out.
Responses to reverse keyed items are counted in the opposite direction.
(4 + 4 + [6-2] + [6-2]) / 4 = 4
(5 + 5 + [6-3] + [6-3]) / 4 = 4
1(strongly disagree) + 5(strongly agree) = 6
** Very tough question to answer! **
(But, we’ll give it a shot in our next class.)