Saturday, January 21, 2006

Some Recent BLS Trends Charts

Here are some recent trend charts and links that are worth some study.

1. BLS - Consumer Price Index - this is one of 5 charts from the BLS MLR Editor's Desk posted on Friday January 20th. These show up in the weekly BLS Update. The next two charts come that source as well. This uses the year over year percent change which produces some smoothing of the raw data.

I like the longer time period. I also like the fact that the BLS also provides a link to the data for this one factor that is moderately easy to use for further analysis and reporting for those who might be interested. In my experience, including the data is pretty rare with charts on the internet these days, so my hat is off to the folks at BLS for this nice feature.

I also like the fact that they used the unadjusted data. When doing the year over year calculation, the seasonal adjustment often just adds complication and possible confusion.

What do you see when you look at this graph? What recent trends stand out?

2. BLS Produce Price Index - Here is a second chart from the BLS MLR Editor's Desk for the past week. It has the same good features as the previous one - long time interval, year over year percentage change for smooth, not seasonally adjusted, and a link to the data in a moderately easy to use format.

What trends to you see at work? How does this chart complement the previous one for CPI?

3. Real average weekly earnings, December 2004 – December 2005 - here is a third chart from this week's BLS MLR Editor's desk. This one tells a pretty clear story, but it's not nearly as good as the previous two charts.

Some things I liked:

3.a. the use of a full year of data for each data point rather than focusing on change of the most recent month as is so often the case in reporting on these metrics.

3.b the inclusion of the data set (albeit only 5 data points)

Here are some things I find weaker on this chart than on the previous two charts:

3.c. The shorter time period only covering 2001-2005 rather than 1996-2005 - this would double the number of data points. For showing only yearly data, an even longer period and more data points might well be a useful thing to consider.

3.d the use of yearly data rather showing the 12 month change on a month by month basis as the other two charts do. If a longer period of 1996-2005 had been shown and monthly data used, we would have had 120 data points in the series rather than just the 5 that were used.

3.e the use of seasonally adjusted data rather then using year over year for smoothing. With monthly data showing year over year change, there is likely no need to invoke the complicating step of seasonally adjustment.

3.f the lack of mention on the chart itself that tells the viewer it is seasonally adjusted data. The information is in the text of the brief article at the link address, but could easily be overlooked.

BLS publishes their update every week. I find it worth taking a regular look. Looking at these three charts together gives some degree of multi-dimensionality but far less than I think is called for if we wish to understand CPI, PPI, or real average weekly earnings. Each of these could use a treatment that included the top 10 related factors - all shown on the same time scale.

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