# Small Multiples – Abortion Data 1980-2003

Jorge used some U.S. Census Bureau data (original Excel file) to visualize the abortion ratio as a small multiples chart.

I like this chart as I am a big fan of small multiples displays. They help us to understand the nature of multi-dimensional data.

Jorge asked for suggestions to improve his chart and I came up with these:

• The abortion ratio is calculated as the number of pregnancies that end in an abortion per 1000 pregnancies. I would put the definition of the ratio in the title or a footnote (Number of abortions per 1,000 live births). Most places where I have seen this data presented tend to do it in this way too, although my preference would be for a % format.
• I think that the data for Race, Marital Status and Age Group are actually 3 different stories. It took me several scans of the whole chart set to realize this. I would add some white space between the Age group charts, the Race and Martial Status charts, to make it clear that are comparing different variables.
• Jorge shows an integrated line chart for Marital State and for Race but a small multiples chart for Age Groups. For a more consistent chart reading I would use small multiples charts for all variables.
• The axes of the Percent Distribution bars are not labeled, and have no scale. This coupled with varying meaning of the color encoding is confusing. The percentage distribution data for the Age < 15 lies around the 1% level and so cannot be seen on this scale even though data does exist. We also cannot encode the way this measure also varies with time over the same period. In fact we miss the fact that for women over 25 years the percentage distribution is actually increasing.
• I’m not sure if you need to show the all age groups in the Age group charts as light Grey lines. I know that you want the reader to compare the current age group in the context of the other age groups but this exactly what the small multiples are for anyway.

I like Jorge’s idea of integrating the abortion ratio and abortion percentages, but I found having another group of small multiples provides a more consistent view. If we don’t have the percentage distribution numbers then we can easily draw the wrong conclusions about the data.

Here my small multiples chart for the Abortion by Age Groups:

Update 6/22/2008: Jon Peltier posted on Re: Abortion Ratios 1980-2003 and Interactive Multiple Line Chart some nice Excel techniques to create interactive charts to analyze the Abortion data set.

## 9 Replies to “Small Multiples – Abortion Data 1980-2003”

1. Andreas, one of the goals of this exercise was to test a way to combine a single data value (a proportion), that can be very low, with a growth rate or a ratio that can be very high but misleading (this is a very common real-world situation, and the media love them…).

Your small multiples chart displays a more complete image but one may argue that proportions in the last years are relatively stable and we may not need to see the whole time series.

This is where chart design meets information assessment and my fundamental argument over the last years: you can learn some tricks, you can memorize some best practices, but if you don’t know what to do with your data that will be seen in each of your charts.

I believe that small exercises like this (Nathan, over FlowingData, had a similar one last week), can raise awareness for better data management and data reporting skills. Let’s do it more often!

2. your preferences for percentages notwithstanding (and percentages of what? i must ask), demographic rates and ratios are generally calculated per 1000 population. presenting the data as a percentage is simply confusing and inconsistent with nearly all published research.

also, you have presented three different – and conflicting – definitions for the abortion ratio. per the CDC, the abortion ratio is the number of abortions per 1000 live births, *not* the number of abortions per 1000 pregnancies (a number which would be difficult to calculate, as many pregnancies end in spontaneous abortion before the woman knows she’s pregnant), or as you alternatively present it, the “number of abortions per 1000 abortions and live births,” which does not account for known pregnancies that end in miscarriage or stillbirth.

the abortion rate is the number of abortions per 1000 women of reproductive age (15-44).

your charts are pretty, but because you have ignored standard definitions, they are meaningless from a general usage standpoint.

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