Should the GRO Birth Index year be entered as birth year?

Question

The GRO Index, both the old and new versions, is the cornerstone of genealogy in England and Wales. So much so that for years I have been making certain assumptions based on GRO Index data. For example, I have been using the birth registration year as the birth year in my genealogy database. I am well aware that the year of registration is not necessarily the same as the year of birth, but it was an approximation I was willing to make. From looking at other people's family trees, I am certainly not alone in assuming birth registration year equals birth year.

How much of a mistake is it to make this approximation? Why or why not might this approximation fail? How should birth years be entered in my genealogy software if the only information I have is the quarter and year of birth registration?

Answer 1

Using birth date and birth registration data from my one-place study, I was able to assess how many births occurred in the year they were registered. The data is from all the individuals on the 1939 Register in an East Midland parish, born more than 100 years ago (1916 or earlier). The corresponding GRO birth index entry was located for each 1939 Register entry. I was able to match birth dates with birth index entries for 211 individuals in the parish in 1939.

First, I looked at how many births were registered in the quarter in which they occurred. For example, how many of the January births were registered in March quarter. This is easiest displayed graphically. From this we see the expect trend – births that occurred at the beginning of the quarter were registered in that quarter, while births that occurred near the end of the quarter tended to be registered in the following quarter. From this we can see that, for example, 100% of April births were registered in June quarter, while only 13% of June births were registered in that quarter:

More interesting to look at is the subset that were born in a different year to the registration. Unsurprisingly, these births were those registered in March quarter that correspond to births in Oct-Dec of the previous year. Interestingly, 100% of December births in this dataset were registered the following year, while 33% of November births were also not registered until the following year:

Finally, looking simply at the percentage of births registered per quarter that actually occurred in that quarter:

-------------------------------------------------  
 Quarter | Born in quarter | Born before quarter  
------------------------------------------------- 
 Mar     |       72%       |       28%  
 Jun     |       58%       |       42%
 Sep     |       53%       |       47%
 Dec     |       60%       |       40%

From this we can see that 28% of March quarter births actually occurred the previous year. From this data, I would conclude that it is reasonable to assume that the birth registration year is the same as the birth year only if the birth was registered in either June, September or December quarters. However, there will no doubt be a small number of exceptions where even this assumption fails. For March quarter births there is high likelihood that the birth did not occur that year, and should not be entered into our family trees without some indication that the year is an approximation.

Answer 2

As you suggest the quarter of registration provides direct evidence of that fact only - when that particular registration took place, not of the birth date of the child.

Given that local registrars can register a birth up to 12 months after the event (originally the limit was 6 months), and at any time at all with the permission of the Registrar General and that re-registrations will create a new index entry that can be years after the event then using the registration data as evidence to support a birth date is always going to be a matter of assumption and approximation.

But your analysis does show that in all quarters, using the quarter itself e.g. Jan-Mar 1869 is statistically more likely to be correct than than not, as all the "born in quarter" findings are above 50%.

It would seem to be the best option to use such data, whith a suitable caveat in any published copy.