This article provides a detailed table containing estimations of how many observations are needed to obtain an increased reliability coefficient for situations such as observational data collection in the classroom. A SPSS program is provided for users to analyze situations where an initial reliability value is obtained and the user wants to determine how many more observations are needed to reach a required level of reliability.
Walker, David A.
"Estimating How Many Observations are Needed to Obtain a Required Level of Reliability,"
Journal of Modern Applied Statistical Methods: Vol. 7
, Article 12.
Available at: http://digitalcommons.wayne.edu/jmasm/vol7/iss1/12