How odds and percentages can sometimes hide the big picture away from our eyes was the topic of an earlier post on Down Syndrome. Today, we continue from where we left off.
The data we analysed were livebirth from 10 states in the united states. That approach has a few issues. First, it included only 10 out of the 50 states. Second, and perhaps more importantly, the data covered only live births. In other words, there could be a survivorship bias to the data. What if children born with Down syndrome from different age-group-mothers have different chances of survival? Can it turn our analyses and insights upside down? Well, we don’t know, but we will find out.
Updated Data Including Stillbirths
Last time we sampled 10 states, 5600 live births and a total of 4.4 million mothers. Here we widen our net to cover 29 states, 12,946 births (live births and stillbirths) and a population of 9.8 million mothers. The messages are:
Women above 40 risk about 12 times higher than those younger than 35 to have babies with Down Syndrome. Yet, 54% of the mothers were 35 years or younger.
Not Done Yet
Is this all before we claim a logically consistent analysis? The answer is an emphatic NO. We still miss a major confounding factor that can potentially lead to a survivorship bias. It is the increased use of prenatal testing and termination of pregnancy for women older than 35. What we see at the end could be biased statistics of the probability distribution. So, the work is not done yet, and we will do more research in another post.
