Evidence-based Genealogy - part 2: types of evidence

Sunday 10 March 2019 by Fouke Boss

Evidence can be categorized into several types: direct, indirect and negative. These types, and the way Centurial supports them, are the subject of this blog.

Claims

In the first part of this blog, we discussed how information and claims only become evidence when they are correlated to a specific person and research question. There are however more than one ways for these claims to become evidence.

Direct evidence

The most straight forward way to use claims as evidence is called direct evidence. Direct evidence is evidence which answers the research question at hand directly. When researching the birth date of a certain person, say the painter Vincent van Gogh, an obvious example would be to find a record or other type of source that states the birth date to be 30 March 1853:

By entering this claim into the claims editor of the source screen, like so...

... Centurial will, after correlation, use this claim as direct evidence for the birth date:

Indirect evidence

But there is more evidence to be squeezed out of information from sources than just answering certain research questions directly. By combining claims and conclusions, and by using logical reasoning and common sense, we can arrive at new conclusions without having direct evidence to support it. This type of evidence is called indirect evidence.

As an example, let us look closer to the direct evidence for the birth of Vincent van Gogh. The claims in the birth certificate allow us to conclude that the painter was born on 30 march 1853 in the village of Zundert, the Netherlands. Now most of the time, children are born in the village or city where the parents are living at that time. So this birth place and date of Vincent van Gogh are indirect evidence for the residence of the parents:

Now one might argue that we are not at all certain that this indirect evidence is true. Of course this is not certain, but it is important to realize that every kind of evidence might be false. Even direct evidence from an original source might be false, perhaps because the registrar made a typo or some other kind of error. This is exactly why Centurial allows every piece of evidence, direct or indirect, to be marked as 'not plausible'.

In the end it is up to the genealogist to weigh all the available evidence and to come to a conclusion. And it would be very wrong to ignore any available indirect evidence in that process. Perhaps the available indirect evidence might prompt a new search for additional evidence to sort out a certain conclusion.

Claim-based indirect evidence

Centurial also supports a special type of indirect evidence, namely indirect evidence that is based on a single claim. For example, a source might state the age of a person at a certain moment in time, usually on the source date. The birth certificate of Vincent van Gogh claims that his father, Theodorus van Gogh, was 31 years old at date of the creation date of the birth certificate, which is 31 march 1853. Now although this does not state the birth date of Theodorus directly, it does give a clue about when Theodorus was born. So Centurial turns this claim single into indirect evidence for the birth date of Theodorus:

So even if we were never to find any direct evidence for the birth date of Theodorus, we would always have this piece of evidence to at least give us a rough idea. Also, when we do find direct evidence, and it turns out the birth does not fall in the range provided by the indirect evidence, this might be a clue that we found evidence about a different person all together.

Indirect evidence for birth date

Centurial currently (v1.9) supports these types of indirect evidence for birth dates:

Type Reasoning Example from Centurial
From age If we know the age of a person at a certain date, we can deduce a range for the birth date. The original source [15] contains a primary claim that the age is 31 years on 31 March 1853. This is indirect evidence for the birth date to be between April 1821 and March 1822.
From baptism As baptism is usually performed within a week or 2 after birth, we can deduce a date range for the birth date of a person from the baptism date. The baptism date is 2 October 1901 which is indirect evidence for the birth date to be between 18 September 1901 and 2 October 1901.
From children Women can generally only have children between the ages of 15 and 45, although of course exceptions do occur. For men, this range is somewhere between 15 and 65. Based on this observation, the birth dates of the children of a person are evidence for the date range in which the person him/herself was born. On average men have children between the ages of 15 and 65, this is indirect evidence for the birth date to be between 30 March 1787 and 17 May 1852.
From vital status Some sources claim the vital status (alive or deceased) on a certain date. Of course, the birth date is always before that date. The original source [7] contains a primary claim that the vital status is alive on on 19 February 1914. This is indirect evidence for the birth date to be on or before 19 February 1914.

Indirect evidence for death date

Centurial currently supports these types of indirect evidence for death dates:

Type Reasoning Example from Centurial
From burial Humans are usually buried within about 9 days after they die. So from the burial date we can deduce a reasonable range for the death date. The burial date is 2 March 1988 which is indirect evidence for the death date to be between 22 February 1988 and 2 March 1988.
From human life span As humans do generally not get older than 120 years, a maximum death date can be deduced from a perons birth date. Since the maximum life span for humans is about 120 years, the birth date of 9 November 1879 is indirect evidence for the death date to be on or before 9 November 1999.
From vital status A vital status on a certain date is a clue for the death date of a person. The status 'alive' implies a death date after the date of the claim, the status 'deceased' implies a death date before the date of the claim. The original source [6] contains a primary claim that the vital status is alive on on 14 September 1922. This is indirect evidence for the death date to be on or after 14 September 1922.

Indirect evidence for residence

Centurial currently supports these types of indirect evidence for residence:

Type Reasoning Example from Centurial
From birth place As people usually are born in the place where their parents reside at that time, and children usually live with their parents for the first years, the residence of a person can be deduced from his/her birth place and date. The birth date and place are indirect evidence for the residence to be Brunssum on 19 August 1876.
From children As people usually are born in the place where their parents reside at that time, the residence of a person can be deduced from the birth dates and places of his/her children. The birth date and place of child van Gogh, Vincent Willem are indirect evidence for the residence to be Zundert on 30 march 1853.
From death place As many persons die at home or in a facility in their place of residence, the residence of a person van be deduced from his/her death place and date. The death date and place are indirect evidence for the residence to be Auvers-sur-Oise, France on 29 July 1890.
From parents As children usually live with their parents until at least the age of 16, the residence of a person during his/her youth can be deduced from the residence of their parents. Parent Carbentus, Anna Cornelia is known to have lived in Zundert between 30 March 1852 and 18 May 1867. Assuming children live with their parents until at least the age of 16, this is indirect evidence for the residence to be Zundert between 31 march 1853 and 18 May 1867.

Negative evidence

There is a third type of evidence, which is called negative evidence, which is perhaps best defined by an example. If you know persons A and B to be married, and you find a census from a later date stating that only person A is living in a certain house, this is evidence for either a divorce, the death of person B or at least a temporary separation.

Centurial does currently (v1.9) not support negative evidence. This is scheduled for some release later in 2019.

Evidence chains

Indirect evidence can easily create longer chains of evidence. For example, the birth date and place of a person is indirect evidence for the residence of the parents, which in turn becomes indirect evidence for the residence of the older siblings of the person.

This mechanism works quite actively in Centurial, most noticable for residences. By entering only a couple birth places and dates for a family, Centurial deduces the residence for all family members, coming up with a surprisingly complete overview of their whereabouts over the years.

Future and improvements

There are of course more possible reasonings which can be turned into indirect evidence in Centurial, and we will most certainly be looking into that in future releases. Do you have an interesting reasoning of your own, and you would like this reasoning included in Centurial, please contact us!