Volunteering builds social capital which leads to stronger, more resilient communities. In addition to satisfaction for the volunteer, individuals who volunteer can help solve community-wide problems and build relationships. Additionally, volunteering has been linked to health benefits such as lower mortality rates and improved mental health.
Louisville currently ranks 14th among its peers in volunteerism with a rate of 26%. The volunteer rate is calculated from American Community Survey data asking respondents if they have volunteered at least once in the past year.
On this metric, Louisville ranks among the bottom tier of its peer cities 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 are a group that lags behind its peers on this indicator.
Louisville’s rate of volunteerism has slowly increased from 2011 to 2014. However, Louisville’s volunteerism rate is still below the 75th percentile of its peers.
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.
