Sexually transmitted infections are becoming more common in the U.S. Infections can lead to long-term health issues like recurrent dysfunction, dementia, infertility, and even death. This analysis focuses on chlamydia because it is a common and easily transmitted infection that is often asymptomatic (presents no outward symptoms). Chlamydia is also of particular concern for women because it can lead to infertility.
Louisville currently ranks 6th among its peer cities in the number of newly diagnosed chlamydia cases per 100,000 people.
On this metric, Louisville is in the top tier of its peer group according to a natural breaks algorithm. Cities in green are those that outperform their peers. Cities in yellow represent the middle cluster, and those in red lag behind their peers on this indicator.
Generally, across Louisville’s peer cities, the number of chlamydia cases per 100,000 people has risen steadily over the last two decades. In Louisville, the rate started to plateau toward the beginning of the last decade. It now sits at a rate that is roughly equivalent to the average of all of its peers.
Memphis has seen the greatest increase in its annual number of chlamydia cases per 100,000 people over the last two decades. Cases in Memphis began to decrease toward the beginning of the 2010s but are back on the rise again. The best performer, Grand Rapids, has seen an increase of 200 in its annual number of chlamydia cases per 100,000 people. Louisville has outperformed its peers, on average.
For each indicator, Greater Louisville Project assigns cities into one of three groups (high-performing, middle-of-the-pack, and low-performing) based on how they compare to other cities. The assignment is based on how cities naturally cluster on that indicator. Sometimes, the differences between cities are very small, and the difference between a city ranked 5th and 6th could simply be a matter of the sampling error that arises from using survey data. Thus, rather than always make a division that declares the top 5 to be the top tier, we use a natural breaks algorithm to look for a cluster of cities that is outperforming the rest, a cluster that is about average, and a cluster that is lagging. This clustering gives us a better indication of where Louisville is thriving and where Louisville has room to learn from cities that are doing better.
Z-scores (or standardization) is a way to combine data with different units of measurement into a single index. The z-score is a measure of how far away a city (or census tract, etc.) is from the average city. In order to be comparable across different units of measurement, the z-score is the distance from the mean measured in standard deviations (e.g. if Louisville has a z-score of 1 it means Louisville is 1 standard deviation above the mean of its peer cities).
Data from the Robert Wood Johnson Foundation's County Health Rankings use z-scores and all z-scores are relative to the mean of Louisville's peer cities. (On the County Health Rankings site z-scores are relative to all the counties in each state - thus z-scores reported by GLP will be different, because we are using a different reference group). The Greater Louisville Project also uses z-scores in our multidimensional poverty index, which compares each census tract to the mean of all census tracts in Louisville.
