Chelan-Douglas Trends e-Newsletter

U.S. CENSUS NOW OFFERS STATISTICAL SIGNIFICANCE TEST-

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The American Community Survey (ACS), from the U.S. Census, provides estimates for the nation, as well as all 50 states and all counties across the nation. These estimates include various measures of well-being, income, population, diversity, housing, age and more. These are usually averages but sometimes medians which, are used to keep track of important trends throughout each county.

Each year as every ACS-sourced indicator on the Trends site receives an update, the numbers may show a significant change, a small change, or anything in-between. All ACS indicators are estimates based on a national survey. For large populations, the survey provides annual estimates. For smaller populations, the ACS offer five-year moving averages.

For both population groups, the "More Information" section now includes the results of a statistical significance test, making it easier to determine how significant the change in data is. For the two counties combined and Chelan County, this is a test based on annual data. For Douglas County and the two cities covered in the Trends, the test is based on a non-overlapping set of 5 years.

An algorithm provided by the ACS determines whether the change is statistically significant or not. If the estimate is found to be "statistically significant", it means the most recent estimate is different from that of the base year. This is important because this will show that the trend is changing.

One example of an ACS indicator is the Median Age of the Population, which shows a trend of the median age of the population throughout the region, counties, Wenatchee and East Wenatchee, the state and the nation. For each location, a significance test is performed. If the test results come back as "not statistically significant", it means the median age has not really changed over the time interval measured. On the other hand, if the test results are "statistically significant", it means over time the trend has seen change due to real factors. For example, if the median age of the population has gotten older this could be due to medical advances and a better standard of living.

Most every ACS-sourced indicator allow statistical significance tests but not all. For example, some indicators use a combination of more than one ACS table and as a result, the test cannot be carried out. If test results are offered, the test was able to be performed. If no results are offered, the test was unable to be performed.

With the addition of the statistical significance test results, we can now draw more accurate conclusions than previously available about the estimates offered for each ACS indicator. Knowing if changes are actually significant will help the community better understand what's truly going on around in our two counties.