Why are some indicator values missing in my analyses?
To be statistically valid, field normalized indicators need to be based on a minimum of 50 publications. If your selection has less than 50 verified publications for the analyzed period, no value for these indicators will be shown. If you choose to group the results by year you can analyze the trends of different indicators at the cost of precision.
The smaller the sample the more inaccurate is the calculated indicator, especially for field normalized indicators. For a sample size of 100 publications the yearly variation of the field normalized citation rate has been estimated to about 0.2 units for a stable research environment.