On Doing History: Milk Data, Lies, Damn Lies, & Statistics

milk-jpg_171813I seem to have developed a longstanding interest in the history of milk. Inadvertently. Unintentionally. And not really. Let me explain.

During graduate school, I wrote a seminar paper on the swill milk scandal as reported in the media in 19th-century New York, published, among other places, here. Later, my interest in Barry Commoner’s social and scientific activism provided me with opportunity to investigate the Baby Tooth Survey of the 1950s and 1960s, which tested the amount of Strontium-90 in baby teeth as a result of nuclear fallout. As a means of alerting the public the hazards of radioactive fallout, Commoner and the St. Louis Committee for Nuclear Information engaged in a public study of baby teeth. Strontium-90 was a radioactive and calcium-like by-product of the tests that traced a similar path through the biological food chain. Strontium-90 followed calcium from soil to plants to animals, and into human bodies. And especially young bodies through milk consumption, which has long been known to be good for bones, teeth, and hair. Strontium-90 doesn’t offer the same benefits. Instead, it concentrates itself in bones, exponentially increasing one’s risk of cancer. Reading mothers’ letters accompanying the baby teeth is quite a moving experience (these are housed in the Western Historical Manuscript Collection at the University of Missouri-St. Louis). Imagine discovering that the milk you made your child drink might actually contain radioactive poison; parents were terrified and heavily involved. So, for one reason or another, milk keeps popping up in my work. (Interestingly—or, maybe, not—much of my focus on milk stems from its consumption, when most of my research tends toward production questions). To make matters even worse, I am also supervising a dissertation on cheese, which will be excellent.

This is sort of a by-product of my focus on new technologies developing environmental hazards, and there seems to me to be no greater risk to public health than threats to our food systems. Too: this is likely coloured by my being a father, and the heightened risk to small, developing, vulnerable bodies being especially susceptible to contaminants. Milk, especially, is of vital importance to children’s diets.

At any rate, the above serves as context for my pausing to read through a recent Wall Street Journal article on the decline of milk consumption. Note that I run off on a tangent below and that the WSJ article serves only as a jumping-off point. It’s well worth the read, however, and posits some interesting explanations for the decline of per capita milk consumption. In addition, the decline of milk consumption introduces some intriguing retail dynamics. According to the WSJ, milk products were typically kept at the back of stores and were used as a loss leader, enticing customers to walk through the aisles. But, to me, the premise for the whole article was what caught me:

Per-capita U.S. milk consumption, which peaked around World War II, has fallen almost 30% since 1975.

The historian in me wants to trace this decline and explain it. I must confess to initially putting the cart before the horse; given my interest in the Strontium-90 scare of the late 1950s and early 1960s, I wanted to see if this had any impact on American milk consumption (this doesn’t interest itself in the more recent decline, which the WSJ tries to justify). That is to say, is it possible to link reduced milk consumption to the period surrounding the Baby Tooth Survey? The more dedicated historian would be inclined to investigate this data without any predetermined assumptions about what it might yield, lest s/he find ways to skew the data to generate the desired result. There are, after all, lies, damned lies, and statistics. But this is merely a playful exercise in playing with data and thinking historically about it, so I’ll forge on.

As dates for data analysis, let’s start with 1958 (when the Committee for Nuclear Information initiated the study) and conclude with 1963 and the signing of the Nuclear Test Ban Treaty. It might also be worth watching 1961, when Louise Zibold Reiss published the Baby Tooth Survey’s preliminary data in Science. Here’s the data:

Data collected from http://future.aae.wisc.edu/
Data collected from http://future.aae.wisc.edu/

Caveats: I chose—rightfully or wrongfully—to concentrate just on plain milk. Keep in mind that dairy—butter, cheese, yogurt, flavoured milk, etc—is a much bigger and more complex issue. And complexity is a key feature of doing good history. Also, we might examine the politics of breastfeeding over the past century to fully round out this study. Maybe these are important, maybe not. The historian and the focus of the project would need to determine scope and relevance. But cutting corners by skipping variables can be problematic.

Visual data provides exciting opportunity to discuss history. And it raises a number of questions. My initial “guess” as to why milk consumption grew so markedly in the 1940s involved the 1946 National School Lunch Act, which explicitly included milk (up to 2 pints per day) as a free school staple. But milk consumption peaked the year before The Act came into effect. In fact, it seems as though the Act precipitated the decline between 1945 and 1950. In the absence of other information, this provides students with the opportunity to infer what happened. Less milk purchased for home consumption? Or were other factors at play? Proper analysis requires developing a better and more nuanced timeline—reading behind the data to understand the social and cultural politics of nutritional science and how and when various dairy associations and councils lobbied more or less effectively. Raw data doesn’t explain this (though it might help tell us where/when to look for clues).

Another interesting feature of the general decline of milk consumption during the 1950s and 1960s is that it coincided with the square containers, which allowed for the more efficient sale of more milk (cartons made it easier to sell greater quantities of milk for less money than bottles). But still people were drinking ever less milk.

Back to my initial curiosity concerning the influence of the Baby Tooth Survey. It would appear as though nuclear fallout played a limited role. Here is the data on a year by year basis from 1945 to 1965:

Data collected from http://future.aae.wisc.edu/
Data collected from http://future.aae.wisc.edu/. Milk consumption measured in lbs.

The Baby Tooth Survey began in 1958. In 1957, per capita milk consumption was 290.4 lbs, down from its all-time high of 347.2 lbs in 1945. Which is to say that a decline had already occurred. Playing causation and correlation, it is interesting to note that after a relative levelling-off of milk consumption between 1948 and 1957, per capita consumption proceeded to drop steadily from roughly 1958 to 1963, the year the Nuclear Test Ban Treaty was signed. This is more evident in the smaller graph. Witness:

Collected from http://future.aae.wisc.edu/
Collected from http://future.aae.wisc.edu/

From a visual perspective, how you measure makes a difference. While the longer time span does not seem to suggest any correlation between the Baby Tooth Survey and milk consumption, a closer, annual look at the data indicates there could be some kind of connection. But the historian needs more data, more information, and more context. Where would you look for more clues?

It’s also easy to lose sight of what it is we’re examining. Note that this decline occurs during the Baby Boom. One feature of the Wall Street Journal‘s account of the contemporary decline in milk consumption involved an aging population. During the post-World War II baby boom, you would think that there would be an increase in milk consumption. But note: we’re looking at data for per capita milk consumption, which is to say: milk consumed per person. And this is where the Wall Street Journal trips up a little. Here’s a summary of milk production and sales over the same period as the first graph:

Collected from http://future.aae.wisc.edu/
Collected from http://future.aae.wisc.edu/

So milk production and sales have been steadily increasing (and, going back to the long-term consumption graph at the top, only post-Baby Boom, by the 1970s, did milk consumption drop below the fairly steady per capita consumption levels of the 1920s and 1930s). We might infer that increased industrialization and wartime expansion might account for the growth in milk sales and consumption (compare with the consumption table above—both note marked growth during the 1940s) during World War II. Of course, US population has grown steadily since World War II, which accounts for the decline in per capita consumption. But this would indicate that the Baby Boom likely did have an overall impact on milk sales. Curiously, though, the 1946 National School Lunch Act has no impact again, though you might expect to see some increase on this graphic. But we could see the influence of milk cartons in the growth in milk sales during the 1950s and 1960s. Perhaps. This is still rather speculative.

Indeed, none of this is designed to be conclusive; this is all more a think piece and brief discussion of how historians might use data, noting some of the prospects and pitfalls that students should keep in mind. In grading my last batch of history exams, I was struck by the number of students who clearly retained lots of course information, but seemed unable to process it and determine what information was important and what was not. As a result, they threw everything at the wall (or question) and hoped that some of it would stick. Without trying to sound condescending, this is unsatisfactory history. For me, the real pleasure in this kind of analysis is the joy of the hunt: trying to prioritize factors that help explain the numbers. History doesn’t stop at trends of increase or decline; instead it begins there. Historians need explain why events took place.

Historians cannot interpret results that the existing data does not support. But we also need to be careful to ensure that what we are looking at is an honest reading of what data tells us. Similarly, we must consider what we are looking for. I’ll follow up on this in the new year with some data on bicycles and bicycling as part of my bike history courses starting in January. It’s easy to get lost in graphs and data—I love looking at all kinds of statistics. But, increasingly, with more and more information available to the historian in the digital age, the onus is on us to ensure that we can not just present the data, but also explain it. That involves looking into and beyond the data sets.

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