Reliability of sources

Experience shows that information (or evidence) found in genealogical sources can be unreliable. To evaluate reliability of genealogical information one must consider the following: the knowledge, bias and mental state of the informant; the passage of time; the potential for copying and compiling errors; and the type of information.

Knowledge of the informant
The informant is the individual who provided the recorded information. Genealogists must carefully consider who provided the information and what he or she knew. In many cases the informant is identified in the record itself. For example, a death certificate usually has two informants: a physician who provides information about the time and cause of death and a family member who provides the birth date, names of parents etc.

When the informant is not identified, one can sometimes deduce information about the identity of the person by careful examination of the source. One should first consider who was alive (and nearby) when the record was created. When the informant is also the person recording the information, the handwriting can be compared to other handwriting samples.


When a source does not provide clues about the informant, genealogists should treat the source with caution. These sources can be useful if they can be compared with independent sources. For example, a census record by itself cannot be given much weight because the informant is unknown. However, when censuses for several years concur on a piece of information that would not likely be guessed by a neighbor, it is likely that the information in these censuses was provided by a family member or other informed person. On the other hand, information in a single census cannot be confirmed by information in an undocumented compiled genealogy since the genealogy may have used the census record as its source and might therefore be dependent on the same misinformed individual.

Bias and mental state of the informant
Even individuals who had knowledge of the fact, sometimes intentionally or unintentionally provided false or misleading information. A person may lie in order to obtain a government benefit (such as a military pension), avoid taxation, or cover up an embarrassing situation (such as the existence of a non-marital child). A person with a distressed state of mind may not be able to accurately recall information. Many genealogical records were recorded at the time of a loved one's death, and so genealogists should consider the effect that grief may have had on the informant of these records.

The effect of time
The passage of time often affects a person's ability to recall information. Therefore, as a general rule, data recorded soon after the event is usually more reliable than data recorded many years later. However, different types of data are more difficult to recall after many years than others. A data type especially prone to recollection errors is dates. Also the ability to recall is affected by the significance that the event had to the individual. These values may have been affected by cultural or individual preferences.

Copying and compiling errors
Genealogists must consider the effects that copying and compiling errors may have had on the information in a source. For this purpose, sources are generally categorized in two categories: original and derivative. A derivative source is information taken from another source. An original is one that is not based on another source. Each time a source is copied, information about the record may be lost and errors may creep in from the copyist misreading, mistyping, or miswriting the information. Genealogists should consider the number of times information has been copied and the types of derivation a piece of information has undergone. The types of derivatives include: photocopies, transcriptions, abstracts, translations, extractions, and compilations.

In addition to copying errors, compiled sources (such as published genealogies and online pedigree databases) are susceptible to misidentification errors and incorrect conclusions based on circumstantial evidence. Identity errors usually occur when two or more individuals are assumed to be the same person. Circumstantial or indirect is evidence that does not explicitly answer a genealogical question, but either may be used with other sources to answer the question, suggest a probable answer, or eliminate certain possibilities. Compiled sources sometimes draw hasty conclusions from circumstantial evidence without sufficiently examining all available sources, without properly understanding the evidence, and without appropriately indicating the level of uncertainty.