The census survived the end of the Roman Republic and the transition to empire, though it receded in importance. Caesar Augustus considered three censuses, in 28 BCE, 8 BCE, and 14 CE, amongst his life’s achievements. The last recorded a count of 4,937,000 people, a number etched upon stone throughout the empire. In the biblical account of Luke 2:1, Mary and Joseph were called to travel from Nazareth to Bethlehem, because “Caesar Augustus issued a decree, that a census should be taken of the entire Roman world.”
Unlike today’s censuses, ancient censuses rarely counted everybody, often including only, for example, men of fighting age. So while they dominate the theological account, Mary and the infant Jesus would probably have been excluded from the administrative record. Indeed Augustus’ empire was far more populous than his census counts suggest, home to perhaps 50 million people. Around the same time, the first truly reliable census of Han China recorded 59,594,978 people, a number remarkably consistent with modern estimates.
Ancient censuses differed from modern ones in another way: They were usually used to establish and maintain individual entitlements or obligations, of taxation or conscription. People did not like being counted: It was often in their interest not to be, and they might avoid it if they could. But when modern states established national censuses in the 18th and 19th centuries, those individual obligations were left behind. Under the influence of “political arithmeticians” and later statisticians, the census became a scientific, statistical instrument. In the United States, it became an instrument fundamental to the operation of representative government.
Over the 19th century, ever more questions were added to the US census. Coupled with a growing population, old methods of counting could no longer keep up. Census taking had become a formidable engineering problem. In 1890, the census saw perhaps its greatest and most influential technological innovation: counting by electric machine. The “Hollerith tabulator,” named for its inventor, a New Yorker named Herman Hollerith, was about the size of a writing desk. A tall cabinet stacked at its rear gave it the overall shape of an upright piano. The cabinet displayed 10 dials arrayed in four rows and 10 columns. Each dial had 100 subdivisions and two hands, like a clock, which together could count up to 10,000.
The machine was operated by a seated clerk. At the clerk’s right, on the desk’s surface, lay a sturdy contraption with a smooth wooden handle, which Hollerith called the press. At the left was a stack of stiff cards, each one representing a person, with round holes punched out to represent different characteristics of that person: black or white, male or female, single or married, literate or not.
The operator placed each card, in turn, on the lower surface of the press and then pulled firmly down on the handle. As the jaws of the press came together, spring-loaded pins pushed down against the card. Some were blocked, while others passed through holes, making contact with cups of mercury below, closing electric circuits and advancing dials corresponding to the holes.
For Frederick H. Wines, a census employee who saw the machine in operation, this process of counting and sorting people by electricity approached a religious experience. “Under the mysterious influence of the electric current running through the machine, they organize themselves, as though possessed of volition … I can compare this current to nothing less intelligent and powerful than the voice of the archangel, which, it is said, will call the dead to life and summon every human soul to face his final doom.”
Census takers have been studying this kind of data for decades, using it, for example, to estimate undercount error in the census. But there are hurdles to using it as a wholesale replacement for survey data. In the past it has been difficult to reliably link records for the same person in disparate sources—for example, tax returns and school records. Many countries, too, have had legal restrictions on this kind of matching, especially when the underlying records are managed by different agencies. But modern computers allow more powerful matching, while better statistical techniques have been developed to minimize the impact of mismatches. Exemptions are increasingly being crafted to allow matching for statistical purposes.
In the United States, the Census Bureau is hoping to use administrative data to reduce the need for in-person nonresponse follow-up on the 2020 census. If COVID-19 continues to delay and disrupt the census field work, the Bureau may have to make much more extensive use of such records than was originally planned. Whether existing administrative records could entirely replace a survey-based census remains something of an open question. In the US, existing government databases simply aren’t designed for this purpose.
In some countries, however, they are. In the 2010 round, 19 European countries used a “population register” to replace some aspects of a traditional enumeration. Several countries outside Europe, including India and Turkey, have also begun to establish population registers. What distinguishes a population register from other administrative databases and makes it a suitable basis for population statistics is that it includes everyone resident in a country, it is kept continuously up to date, and it can be linked to other government databases and surveys.
But to remain accurate for this purpose, a population register requires mandatory reporting when, for example, a person changes their address. In many countries, including the United States, there is a deep reserve of resistance to such reporting mechanisms—a resistance that the traditional census, with its more limited aims, is often spared. Opponents see a slippery slope leading from mandatory registration and national identity cards to laws requiring such cards to be carried at all times and police checkpoints on street corners.
It’s possible that this cultural aversion to registration is weakening. A poll taken in the wake of the September 11 attacks found a slight majority of Americans in favor of “a law requiring all adults in this country to carry a government-issued national identification card.” No such card was introduced, but federal involvement in driver licensing has partially nationalized what was previously a state responsibility. In a world where terrorism, illegal immigration and, now, suddenly, public health remain issues of serious popular concern, it’s not hard to imagine public opinion shifting further in favor of numbers, cards, and registers.
The traditional, decennial census is almost certainly in the early stages of decline. It’s surprising, really, that this curious invention, with its ancient roots, has somehow survived into the 21st century. In most countries, it will probably, eventually, be replaced by more extensive administrative records. Change may be gradual. Statisticians are by nature fairly conservative, and whatever financial or political pressures they face, today’s census takers are keenly aware that they are the custodians of a centuries-old tradition. In some countries, the United States most prominently, the glacial pace of legislative or constitutional reform will ensure the continuation of some sort of traditional census for some time.