Sunday, April 12, 2015

Some survey data on the public's abortion views

In my earlier post on this subject, I posed the question
For each n = 1, 2, 3, ..., what percentage of Americans would outlaw abortion-on-demand in week n if they could do so? Is there any research on this?
In January, Vox's Sarah Kliff pointed to some partial survey data about this question. Here is the graphic she showed:

This is by trimester, not by week, but the trend is still pretty clear: the later the pregnancy, the more agreement there is that an abortion should be illegal; the earlier the pregnancy, the more agreement there is that an abortion should be legal.

The above data comes from a Gallup Poll that I had missed until now. Here are the raw numbers:

People do love their bar graphs, don't they? Instead, let's look at the data on a scatterplot, since it's really a time-series:

The green circles are the "should be legal" data points, the blue triangles are the "should be illegal" data points, and the black squares show the sum of the two percentages. (To make the graph, I assigned each Gallup data point to the last month in each given trimester.)

There is a lot of blank territory in the region from 0–2 months. One way to estimate those percentages is to fit the data with a logistic curve:

The logistic fit to the data is pretty good, including the "accelerating consensus" effect shown by the u-shaped black curve. (This was to be expected, because the closer you get to the extremes, the less you expect people to dodge the question.)

Here are the extrapolated percentages based on the fit, shown with open circles, open triangles, and open squares:

Based on this exercise, I'd say it's a pretty good estimate that upwards of 80% of Americans want abortion to be legal during the first month of pregnancy. I wonder, then, if abortion rights advocates over the past decade or two have made a mistake by not introducing the time variable more clearly into the abortion debate. In recent years, hundreds of laws have been passed all around the country that make it harder for women to get abortions—regardless of how early they are. It seems to me that this has been a major tactical victory for the 10–15% at the lower left of the diagram.

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