Cronbach's Alpha, first described by Cronbach Lee in 1951, is widely used as a indicator of results reliability (precision). An alpha value larger than 0.7 indicates results are precise and thus, reliable.
This video describe how it works and how would you increase the alpha of your experiment based on the equation alone.
List of references:
Bland, J. M., & Altman, D. G. (1997). Statistics notes: Cronbach's alpha. Bmj, 314(7080), 572.
Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. psychometrika, 16(3), 297-334.
