Alerian’s page showing annual distribution growth for the Alerian MLP Index (AMZ) contains their most popular chart (it’s the 4th one down under “Figures and Tables”). It’s no wonder – the steadily growing distributions it portrays should be enough to calm any income seeking, excitement-averse investor. Since it’s their most viewed page, many investors must have drawn comfort from the reliability it presents. The turmoil endured by MLP investors since 2014 appears incongruous when such steady growth in payouts is considered.

Oddly, investors who hold securities linked to the index (such as the JPMorgan Alerian MLP Index ETN: AMJ) have not enjoyed the distribution growth presented by the index. It’s because of Alerian’s curious method of calculation.

The components of the index are updated periodically based on criteria set by Alerian. The growth figure they calculate takes the index members at the end of the year, and looks back to calculate the year-over-year growth rate they experienced. Some of those names may not have been in the index over the prior two years, and perhaps more importantly those names that have been dropped (often because they cut their payout) are excluded.

The distribution growth rate therefore reflects what today’s index members are growing at. This may be useful information, but it’s not the same as calculating the growth rate of distributions received by investors in the index. Moreover, it creates an upward bias to the calculation, because poorly performing names who cut their payouts are dropped while recently IPO’d high fliers are included. During the 2015-16 MLP collapse Alerian relaxed the requirement that any AMZ member cutting their distribution be excluded, probably because it would have led to an overly concentrated index.

“When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean—neither more nor less.” It’s Growth Through the Looking Glass.