Retrospective appraisals are appraisal reports that are completed as of a prior date or a date in the past.  Historical appraisals of this type are often ordered for litigation or for IRS tax reporting purposes. 

Rent comparability studies or RCS studies, are studies requested from appraisers on both residential and commercial properties.  Usually a client wants to know what the market rental rate is for his real property.  Rental rates become important to owners and tenants when lease options are renewed or when they are intially negotiated. 

Some appraisers offer both appraisals and market feasibility studies (MFAs) as part of their appraisal consulting services.  MFAs are studies of specific markets and they answer the question "will the market support the profitable use of my proposed development?"  If you are going to spend hundreds of thousands or millions of dollars constructing; an elderly care facility, an RV park, an apartment complex, a storage facility or other specialized building improvement you need to know (beyond a guess or cursory analysis) whether success is or is not attainable.