How to Read an NM-IBIS Indicator Graph
If you go to any NM-IBIS Indicator Report (which you can do from the Indicator Reports A-Z Index) you will see a graph. The typical graph, such as the one below, shows the New Mexico trend over time along with the U.S. trend over time. In epidemiology, we tend to look at "Person, Place and Time." So many of the NM-IBIS indicator graphs will provide indicator data with different graph views for different people (e.g., by sex and age), places (e.g., statewide and by county) and different time periods (e.g., a trend graph).
Please feel free to contact us
with questions or suggestions.
Parts of a GraphBelow is a typical graph from an actual NM-IBIS indicator report. There are different kinds of graphs, such as pie graphs, line graphs, and bar graphs. The graph displayed here is a line graph.
- The Title. The first thing you want to look at is the title. A good title will tell you what the graph is about, as well as the population measured and the measurement period. The graph below is about births to two age groups of teen-aged girls in New Mexico and the U.S., measured from 1990 through 2013.
- The Y-Axis. Next, look at the Y-axis. Graphs are displayed in
2 dimensions (height and width). These are also called, "axes," with a vertical, up and down,
or "Y" axis and a horizontal, left-to-right, or "X" axis. The Y-axis tells the the reader
about the data in the graph. Our graph is showing the number of births per 1,000 girls in
the population, also known as a fertility rate, and commonly called the "Teen Birth Rate."
Looking closer at the Y-axis, you will see numbers (0, 20, 40, 60, etc.) going up the side. These numbers tell the reader about the data values. For instance, the left-most dot on the top (yellow) line has been plotted between 120 and 140. That dot indicates a teen birth rate of about 125 births per 1,000 girls in that population.
- The X-Axis. The X-axis is the horizontal axis. The numbers along
the X-axis on our graph are years, 1990-2013. So this graph shows the trend for teen birth rates
for the time period from 1990 to 2013.
It is also important to note that the X-axis intercepts(crosses) the Y-axis at the value "0." This is not the case with all graphs, but it is will be true for all NM-IBIS graphs.
- The Legend. There are four lines on the graph. The legend tells us that the top (yellow) line represents New Mexico mothers aged 18-19 years. So right away, we can see that teen birth rates are higher for New Mexico 18-19 year olds than for the other groups. Also, from looking at the top line, we can see that the fertility rate for that population group has declined over time, with an increase from 2004 to 2007, but otherwise showing an overall decreasing trend.
- Confidence Intervals. The confidence intervals are represented on the graph by the small vertical lines that run through each data point. They're easiest to see on the top line, and they have not been reported for the two U.S. lines. The confidence interval may be thought of as the range of probable true values for a statistic. In this case, the confidence intervals New Mexico mothers aged 18-19 years do not cross the trend line for the U.S. mothers in that age group. That tells us that the New Mexico teen birth rates for mothers age 18-19 are statistically significantly higher than the U.S. values for that age group.
- Data Notes. You will also want to read the graph footnotes before you make a final interpretation of the data. The Data Note under our Teen Birth Rate graph indicates that the rate includes only live births, and does not include all pregnancies. Often, we refer to "teen pregnancies." But we typically have data for only teen births.