After the 1990 Census, the San Jose Mercury News had charted the changes and breakdowns of our diverse area. A few years later, Miranda Ewell wanted to look at what has happened since then in the workplace and in our neighborhoods. After testing a few different measurement tools, I decided to try applying a diversity index to our populations.
I chose the USA Today Index of Ethnic Diversity developed by Philip Meyer of the University of North Carolina at Chapel Hill and Shawn McIntosh of the Dallas Morning News. The USA Today diversity index eliminates the need to analyze the distribution of several factors with one probability-based index.
"The index has a range from 0 to 1, and its value represents the probability that two people chosen at random from the study population will differ along at least one ethnic dimension." (International Journal of Public Opinion Research, Spring 1992).
We chose this index because it seemed to both show trends of diversity and be easy enough to explain to readers in a few paragraphs.
Here's the formula to calculate the Index of Ethnic Diversity which we applied to each Census tract:
Step 1: Probability that two persons chosen from a population at random will be members of the same racial group: P. R = (A2+B2+C2+D2) where A, B, C & D are the proportions in the population of whites, blacks, native Americans, and Asians or Pacific islanders.
Step 2: Probability that two persons chosen from a population at random will either be both Hispanic or both no Hispanic. This is a separate value because Census questionnaires ask Hispanic origin in a different question from race. Therefore it is possible to be both white and Hispanic or black and Hispanic.
P=(H2+N2)
Step 3: Calculate the probability that two randomly chosen persons are the same in both race and Hispanic/non-Hispanic status: PR * PH Subtract the result from 1: 1 - (PR*PH)
We created a spreadsheet with the populations and put the formulas into the spreadsheet. We applied the index to our local county totals, but also took our results by Census tract and mapped them to show the clusters of diverse areas.
We also applied another measure to the counties of a whole over time: the Dissimilarity Index. This is another index from 0 to 1 - the closer to 1 the higher level of segregation in an area. For both Asians and Hispanics, the index has increased. The data also showed decreases for blacks; however, our county has too low a black population for most statistical measures to be accurate.
So why would you want to do any of this instead of general ethnic breakdowns for your area or even mapped for small areas like Census tracts. Those measures don't really show clustering over the mix of different populations. This would show low diversity for areas that are all Asian in our area or mostly white. This index provided a different look at our area. In addition this Index can be applied to other demographic measures, not just race and ethnicity.
To view the on-line version of the Mercury News piece on diversity, go to www.sjmercury.com/news/local/census/index.htm
Technology also changed the way we brought this story to the reader, in addition to showing maps in the newspaper, readers could go on-line, click on their neighborhood and see what the demographic breakdown is. This is something we just couldn't do on paper.
Jennifer LaFleur can be reached at (408) 920-5000 or send e-mail to jenster@sjmercury.com