The distribution of households living at various levels of poverty has been extensively studied. Similarly, the distribution of households receiving food stamps (enrolled in SNAP) is also well known. Not surprisingly, these populations have considerable overlap; eligibility for SNAP is based largely on income, and therefore, correlates strongly with poverty level. But there are scenarios where a household may live below the poverty line and opt not to apply (or not qualify) for food stamps. Conversely, there are situations where household income raises a family above the 100% poverty level, but due to non-financial factors (e.g., disability, employment status), the household can still receive food stamps.
In the top two maps, I show the raw county data: percentage of households living below the poverty line and percentage of households receiving food stamps. Using subsets of data provided by the Census, I was able to calculate the overlap between the groups – those households that are both below the poverty line and enrolled in SNAP – and mapped the values as percentages of each respective group. The result (bottom two maps) provides the percentage of households below the poverty line that receive food stamps (left), and the percentage of households enrolled in SNAP that are below the poverty line (right).
The top maps show that it is more common for a household to be living below the poverty line than to receive food stamps; this is not surprising, as it is much easier for a household that is below the poverty line not to apply for SNAP than for a family above the poverty line to qualify for SNAP. So, in general, a household is more likely to be below the poverty line than to get food stamps, making the top left map darker than the top right map. Despite these differences, the variables are still well correlated (r^2 = 0.67).
The two calculated percentages, however, have only a weak correlation (r^2 = 0.17). This is where the data show some interesting results. If the trend described in the previous paragraph held true, the bottom right map should typically be darker than the bottom left map; because there are fewer households receiving food stamps than living below the poverty line, there should be a higher percentage of households enrolled in SNAP who are below the poverty line than the percentage of households below the poverty line who are enrolled in SNAP.
As a consequence, any regions where the bottom left map is darker than the bottom right map indicates a region that contradicts the norm. States such as Oregon, Michigan, and Maine, represent regions where a household is more likely to be enrolled in SNAP than living below the poverty line. This suggests that these states have unusually high percentages of households above the poverty line who are receiving food stamps.
Data source: http://factfinder2.census.gov/faces/nav/jsf/pages/index.xhtml (Table S2201)