IIf you want your research to hold up under criticism, or be accepted in a court of law, you must pay close attention to professional genealogical standards.

First, there are a few definitions and distinctions you should know. In the past, many researchers used the terms “primary source” and “secondary source” to describe record sources and to evaluate their strength as evidence. We now believe that these terms are misleading.

Definitions and distinctions

Instead of asking whether a source is “primary” or “secondary,” now we think it’s better to ask three separate questions.
Is the source “original” or “derivative”?
Is the information in the source “primary” or “secondary”?
Is the evidence provided by the information “direct” or “indirect”?

An original source is the first recording of an event (in other words, this is the first time anyone wrote down the information). A derivative source is any source that gets its information from previously existing sources. There can be many degrees of derivative sources, from the most basic image copy (such as a photocopy) to a collection of information taken from many sources (such as a published family history).

Primary information is information provided by someone who had first-hand knowledge because he or she was there at the time. The person was either a participant or an eyewitness to the event. Secondary information comes from any other source, including hearsay, family tradition, or previously recorded sources. So, for example, primary information about a wedding would come from the bride and groom themselves, or someone who attended the wedding. A cousin who just heard about the wedding by telephone has only secondary information.

Direct evidence is evidence that doesn’t need any interpretation or analysis to answer the question. It is a direct statement of fact. Indirect evidence is relevant, but requires either interpretation and analysis or additional evidence to support or correct it in order to answer the question. So, for example, a church marriage register that says “John Brown, son of George Brown” provides direct evidence that George Brown was John Brown’s father. But if the church register says John Brown married Ann Smith and the witnesses were George Brown and John Smith, we have only an indirect clue as to the relationship between John Brown and George Brown.

In another example, you know that John Brown and Mary Brown were brother and sister, and you find a record that says Mary Brown’s father was George Brown. That record does not provide direct evidence of the relationship between John Brown and George Brown. You have to “put two and two together” to interpret the record. So it is called indirect evidence.

Principles for evaluating evidence

Here is a summary of the principles professional genealogists use to evaluate evidence:

Original sources are usually more reliable than derivative sources.

The more processing a derivative source has gone through, the less you should trust it (for example, if many hand-made copies have been made, there are lots of opportunities for copying mistakes).

A few pieces of good quality evidence are better than many pieces of weak evidence.

Information is more reliable if it is provided by people who have first-hand knowledge.

A record is only as trustworthy as the person who created it.

It is important to know why a record was created, because it could be biased in a way that makes it more or less truthful.

A record made right at the time of the event is better than one made many years later because memory can be faulty.

A carefully created, maintained, and guarded record is generally more trustworthy (because there is less opportunity for someone to change it).

A record made under oath or during a formal ceremony is generally more reliable than a record made casually (because people are taking the situation more seriously).

Direct and indirect evidence can carry equal weight. One is not necessarily better than the other. But you need to be aware of the difference between them so that you can watch out for mistakes in interpreting of indirect evidence.

The Genealogical Proof Standard

Professional genealogists evaluate the quality of family history research according to the Genealogical Proof Standard. Here is a summary of the “GPS”:
Researchers must make a reasonably exhaustive search for relevant sources of information relating to the particular genealogical problem.
It is important to not stop the research as soon as you have found a record that seems to answer your question. You need to check a wide variety of sources, where possible. This is because any one source, even an original source with primary information that provides direct evidence, can be wrong. Your conclusions will be stronger if you base them on several separate sources. Be careful to make sure that each of your sources didn’t get its information from the same person or another record. If you make a reasonably exhaustive search it is less likely that someone else will find a record later that disproves your conclusion.

Source citations have two purposes:
to identify the specific location of each piece of information (so it can be found again and checked, if necessary)
to allow you and others to evaluate the information.
This means you should provide the following minimum information about each source:
the creator(s) of the record,
the date the record was created,
the place it was made,
the title or description of the record and
the format of the record (whether original or derivative, official, printed, electronic, manuscript, microfilmed, oral audio-taped interview, etc.).
When citing published sources, you also need to record the publisher’s name, date and place of publication, and volume, issue, and page numbers.
For manuscript or government sources, you also need to include the name and location of the repository (the library, archives, or house where you found it), the name and reference number of the collection, and the file or document name and number.

You must also record any information that might affect the interpretation or use of the information. For example, if a manuscript has faded so badly that it is difficult to read, you should say so. You should explain whatever you know about the process by which the records were created and/or the reason(s) for which they were created (you only need to do this the first time you cite a particular source). So, for example, you should note the difference between a private personal diary, a journal that the writer planned to publish and a log kept as part of the writer’s job

You must provide citations for each and every piece of information. Don’t just list all your sources at the end of a paragraph that includes a variety of facts, because it won’t be clear which fact came from which source. Only cite the actual source you personally examined, in the format in which you examined it. If you used a derivative source, you should say so. If you know where the original is, you should add this information, but make it clear that you didn’t actually see the original.
Evidence must be based on reliable records, and interpreted correctly.  

In order to accurately interpret the evidence, you must carefully consider each record and piece of information. Sometimes this means you’ll need to have a lot of information. For example, you might need to know:

the history of the time,
how and why the records were created,
who was in charge at the time and place,
where the boundaries of the area were,
how to read the handwriting,
the terms people used to refer to different kinds of relatives,
legal concepts and regulations,
customs of the people and what records are available.

Each time you find a new source, you need to think about the reason it was created and whether the person who created it likely knew what he or she was talking about. Was there any bias? What reasons might the informant have had to lie or record false information?
If the information is secondary, you should try to find out how many times the information was repeated before it was recorded (the fewer, the better).

aren’t allowed to see it), you should try to use exact image duplicates (such as microfilmed records). If you can’t find these, try to find an official copy made at the same time or soon after the original. Finally, if that’s not available, look for other sorts of copies, transcripts, extracts, abstracts and so on.
Conflicting or contradictory information must be resolved or shown to be false.

A clearly reasoned and carefully explained proof argument must be written out.