Help With Viewing Birth Defect Information
Map shading
Different classification schemes can be used to group data on for display on a thematic map (a map which focus on a single theme). There is no single best data classification method; each has advantages and disadvantages. When creating a thematic map, the user should consider the purpose of the map, the data distribution (if known), and the knowledge level (i.e., mapping and statistical awareness) of the intended audience.
Equal interval classification
A thematic map classification scheme where the data are divided by the desired number of data classes, so that the data ranges in each classes is the same (e.g. 10-20, 20-30, 30-40, etc.). The major advantage of Equal interval classification is that the equal intervals are easy to interpret. The major disadvantage of this method is that the data distribution is not considered when determining class breaks for the intervals (only the lower and upper data values are used). This method can be adapted to deal with outliers by truncating the ranges at the upper and lower end of the distributions. Most appropriate with a sequential color scheme.
Percent difference from the mean classification
A thematic map classification scheme where the scheme the data are grouped into intervals by the percent increase and decrease from the middle range, typically the mean. The major advantage of this classification method is that by using the mean as a dividing point, a contrast of values above and below the mean is easily seen. Most appropriate with a divergent color scheme.
Prevalence
The total number of cases of a disorder in a population at a specific point in time or time period, divided by the total number of individuals in that population at that time. This estimate is typically multiplied by some value, such as 10,000, so that the final estimate is the number of cases per 10,000 individuals at risk.