We expect to find alternate spellings of our ancestors' names in census and other records. Lately however, I was startled to find another set of records that may have much more wrong than a simple, unintentional name misspelling. I recently read “Going to America” by Terry Coleman, which is available on www.Ancestry.com. This book describes emigration from Britain to North America largely from 1840-1860, a period that encompasses the Great Irish Potato famine. In large part due to the famine, the number of people fleeing Great Britain spiked in the early 1850s.
The problem, as outlined in the book, was that passenger lists were sometimes falsified. According to the laws at the time, the number of passengers allowed on a ship was determined by its size. Unfortunately for the emigrants, unscrupulous passenger brokers and ships' masters often colluded to skirt these regulations. Brokers customarily received a commission for berths sold, but sometimes a broker chartered an entire ship in which case he “packed into that space as many passengers as the law allowed, or really, as many as he could get away with.” 
Government officials were supposed to inspect ships prior to departure to ensure they carried no more than the allowable number of passengers and also to check that sufficient supplies of food and water were on board. However, too many ships, often all leaving on the same tide, and too few inspectors meant that regulations were often meaningless. In case an emigration official did attempt to inspect a ship there were two common ways in which brokers and ships' captains circumvented the Passenger Acts. One was to hide emigrants on board until the inspector left the ship. Another trick was to state that some passengers were children, even when they were not. This strategy was effective because during these years children were allotted one half to two-thirds of the space of an adult. If more passages were sold than space allowed, the ages were simply altered to meet regulations. Among evidence cited by Coleman are statements made by a steward in a complaint against the Harnden shipping company. “The steward saw a decrepit woman of about sixty who said her name was Eliza O'Neil. On the list she had been put down as under fourteen. He asked Harnden's man if he considered her a child, and the man said to say nothing about it and offered the steward a sovereign. Tansley [the steward] said this was one instance out of many. One family called Bateman was put down as numbering four adults, and as entitled to rations for only four adults, but in fact there were thirteen of them, the youngest about twelve years old, and all had paid full fare.” 
To make matters worse, there were too many ships leaving at once and too few officials to inspect them. In 1847 when twice as many emigrants left Great Britain (258,000) as in any single year since at least 1835 the chief emigration officer at Liverpool (the principal port of departure) had only one assistant to account for the majority of the emigrants. By 1850 he had two assistants, but still “had to cope with more than fifteen times as many emigrants as his colleagues at London.”  By 1852, the peak year for emigration from Britain (at least between 1835-1860), 369,000 emigrants left the nation, most of them through Liverpool.  Complicating attempts to account for passengers, emigration was not evenly distributed throughout the year. Traveling to North America during the winter was dangerous due to bad weather and icebergs in the shipping lanes. Those sailing to Canada were forced to wait for the St. Lawrence river to thaw, which often didn't occur until at least April. As a result, most trans-Atlantic travel occurred during the warmer months. So, not only were two or three emigration officers in Liverpool charged with enforcing regulations on ships carrying the majority of the emigrants who left Britain, the bulk of them left, conservatively, during a seven to eight month period.
Based on statements and reports of the chief emigration officers at Liverpool “in the years 1847 to 1851 the Passenger Acts had been enforced at Liverpool only upon vessels sailing to British North America [Canada], that is to say, on one vessel in thirteen. At by far the most important British emigration port, vessels bound for the United States had done as they pleased. The Passenger Acts had been enforced only if the ships' masters had chosen to enforce them themselves. Neither food nor water had been inspected, and the passengers had not been counted.”  Coleman goes on to write “it also follows that the British government figures for emigration from Liverpool for these years, apparently so precisely recorded, are plainly false. They are nothing more than the adding up of the masters' own statements. There is no saying how inaccurate they are. The Blanche was carrying eighty-six passengers in excess of her lawful complement of 386. [when investigated in New Orleans in 1851] . . . It does seem reasonable to suppose that in the years from 1846 to 1851 ships out of Liverpool bound for the United States may have carried 10 percent more passengers than they were allowed. After 1851 the new emigrant officers at Liverpool. . . tried to be more exact, but even then they cannot have succeeded to the letter. . . there were still only four officers, and if eight vessels often left on one tide, they could not possibly have done their duty.” 
One might imagine it should have been a simple process for the government emigration officials to count passengers as they boarded. This was all but impossible even had ships left at different times. Emigration from Liverpool during this period was, in a word, chaotic. The chief emigration officer at Liverpool from 1845-1851 testified before a 1851 parliamentary committee that “he could not count the passengers, because there was no possibility of getting them together.”  Ships' captains didn't want to be bothered with emigrants until all cargo was stowed and then they apparently wanted to depart immediately. Passengers had to literally scramble aboard while the ship was pulling away from the dock. A medical officer stationed at Liverpool described the scene before the 1851 committee. “[Question] And then he [the captain] proceeds to move his vessel out of the dock before the people have time to get onboard? – [Answer] Very often when she gets to the entrance to the dock where it is very narrow, she is detained there for a short time while other vessels are going out, and during that time the passengers are scrambling in; and I have seen 500 or 600 men, women, and children in a state of the greatest confusion, and their screams are fearful.”  “'In consequence of which we sometimes have dreadful scenes; sometimes the passengers have to watch their opportunity, and when the ship gets near the entrance to the dock you may see men, women, and children clambering up the sides of the ship.' Frequently people fell into the water and occasionally they drowned.” 
The bottom line is that between the monetary incentive to carry more passengers than allowed, too few inspectors, too many ships sailing at once and a record number of emigrants the accuracy of ships' passenger lists suffered. The manifests seem to be more about appearing to comply with regulations than about accurately tabulating the passengers. Unfortunately, the emigrants paid the price for this skulduggery in overcrowded conditions and inadequate supplies.
Clearly ship masters also didn't care about the plight of genealogists trying to catch their ancestors crossing the pond. I suspect, but don't quote me on this, that the closer we approach the present day, the more reliable passenger lists become. The accuracy of these lists probably also depends on the port of departure, the number of emigrants passing through and the number of inspectors. I would like to think that in Germany for example, passenger lists were more reliable. I can confirm the stereotypical German attention to rules. When I lived there, no one, and I do mean no one, even crossed the street if the light at the crosswalk was red.
So, if you have ancestors who you believe emigrated from Great Britain between 1840 and 1860 it is important to keep the above information in mind. You may or may not find your relatives in a passenger list. Even if they are there, you might not recognize them if their ages were altered. While women enjoy being thought of as younger than they really are, I'm sure the emigrants would have preferred having the allotted space and supplies instead.
1. Coleman, Terry. Going to America. 1972. Pantheon Books. New York.