Missing Data Bias References

Hi there. I am currently writing a university level statistics dissertation. As part of the project I collected data on the personal characteristics ( Gender, Age, Sexual Orientation) of staff in a workplace. The method of collecting this data was issuing questionnaires which were not anonymous, however a guarantee was given in the questionnaire assuring that it would be stored securely and only handled by a select group individuals.
As part of the discussion section in the report I would like to include references to research on the Missing data bias of such data collection (since the questionnaire was not compulsory). In particular if there has been research into the fact that certain groups of individuals may be less likely to disclose information like this (eg the LGBT community) and therefore the results may be skewed one way or another for certain charaterisitcs- eg if 70% of individuals responded, and 5% of these reported being LGBT, is this a conservative estimate of the number of LGBT employees since LGBT individuals are less likely to disclose this information, due to perceived judgement or bullying ect.
Does anyone know of any such articles?
Hope thats makes sense.