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Numbers are all around us, especially in the news: A new drug has a 72 percent success rate in treating a disease (but only in patients under 35), while the president enjoys a 48 percent approval rating, even though according to a 2010 poll, almost one in five of the estimated 314 million Americans believe he is Muslim.

We hear statistics all the time, and science studies are often based on them. While some cynics dismiss all statistics as easily manipulated (the famous “there are lies, damned lies and statistics” quote), the truth is that statistics are important and indeed essential to understanding the world around us.

Numbers can be wrong for many reasons, including mistakes, miscalculations, different studies using different definitions, bias in promoting political or social agendas, and, of course, outright fraud. Often, the statistics themselves are correct; it’s how those numbers are interpreted. After all, a glass can be both half full and half empty, depending on how you look at it.

Here are 10 examples of spectacularly flawed statistics that are (or have been) influential and widely believed.

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Worrying about “kids today” is a time-honored tradition. Every generation wrings their hands and laments the wild, immoral and reckless ways of today’s wayward youth. The sky-high rate of teen pregnancy is often cited as a prominent example, along with a list of suspected corrupting influences such as sex-saturated TV shows and music lyrics.

It’s also wrong; the fact is that teen pregnancy is low and has been dropping. Data from the Centers for Disease Control and Prevention’s National Center for Health Statistics found that the birth rate for U.S. teenagers (ages 15 to 19) fell 6 percent in 2009, the lowest level ever recorded in nearly seven decades of tracking teenage childbearing.

The report, “Births: Preliminary Data for 2009” found that the rate for the youngest teenagers, 10-14 years, fell from 0.6 to 0.5 per 1,000, also the lowest level ever reported. The birth rate for teenagers 15-17 years declined 7 percent to 20.1 per 1,000. This rate dropped 9 percent from 2007 (22.1) to 2009, and was 48 percent lower than the rate reported in 1991. In fact, teen pregnancy has dropped 39 percent since its peak in 1990, partly because the most recent studies report that 87 percent of boys and 79 percent of girls use birth control.

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How many homosexual men and women are there in the United States? It’s hard to say. Accurately counting the number of gays is fraught with difficulty for many reasons, including that different researchers use different definitions (Who do we count as gay? Anyone who has sex with someone of the same gender? Only those who self-identify as gay? Bisexuals?), and because sexual activity is private and surveys must rely on often-biased self reports.

Estimates of the percentage of gays by Alfred Kinsey from the 1930s and 1940s concluded that about one in ten American men were more or less exclusively homosexual. This 10 percent estimate, though controversial in some quarters, was widely quoted and circulated for decades.

In his book, “Damned Lies and Statistics,” Joel Best, professor and chair of sociology and criminal justice at the University of Delaware, noted that, “Later surveys, based on more representative samples, have concluded that the one-in-ten estimate exaggerated the amount of homosexuality; typically, they find the 3 to 6 percent of males (and a lower percentage of females) have had significant homosexual experience at some point.... and that the incidence of homosexuality among adults is lower—between 1 and 3 percent.”

A 2011 study by UCLA demographer Gary Gates of the Williams Institute on Sexual Orientation Law and Public Policy concluded that America has approximately 4 million homosexual adults, representing about 1.7 percent of the population.

Gays and the Law: A Bumpy History

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Most of us have, at one time or another, heard someone talk about how our forefathers died so much younger than we do today. Sometimes, for example, it’s used to help explain why many women got married in their teens centuries ago; after all, they had to get started with families early since they’d be dead by 40! According to the National Center for Health Statistics, life expectancy for American men in 1907 was only 45 years, though by 1957 it rose to 66. However, this does not mean that our great-grandfathers rarely lived into their fifties.

In fact maximum human lifespan -- which is not the same as life expectancy -- has remained more or less the same for thousands of years. The inclusion of high infant mortality rates in calculating life expectancy creates the mistaken impression that earlier generations died at a young age. For those with a shaky understanding of statistics, the problem is that giving an average age at which people died tells us almost nothing about the age at which an individual person living at the time might expect to die. The idea that our forefathers routinely died young (say, at age 40) has no basis in historical fact.

Speaking of dying by 40...

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This statistic, in wide circulation since the 1980s, is really, really bogus. As the ever-reliable folks at the rumor-debunking website Snopes.com noted, this little nugget first appeared in a June 1986 article in “Newsweek” magazine titled “Too Late for Prince Charming?” which melodramatically (and inaccurately) claimed that women over forty with university degrees are more “likely to be killed by a terrorist: they have a minuscule 2.6 percent probability of tying the knot.”

The 2.6 percent statistic came from a badly flawed 1985 study which, according to Barbara Mikkelson of Snopes.com, “was contradicted by a U.S. Census Bureau report from about that same time which found... that women at age 40 had a 23 percent chance (at marriage), not 2.6%” The original reference to being killed by a terrorist was, of course, a bit of creative hyperbole not meant to be taken literally.

It’s difficult to calculate a precise percentage chance of women over 40 marrying because there are so many factors involved. Women (and career-minded women in particular) are waiting until later in their lives to get married and have children -- to mention that many of them are either happy being single or are in long-term committed relationships and don’t feel the need to legally “legitimize” their relationships with marriage. In any event, women over 40 (college educated or not) are far more likely to marry than be killed by a terrorist.

PHOTOS: Marriage's Bumpy History

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This weird factoid has been around for over a century. Many people believe that humans have souls, and look to science to confirm their religious beliefs. The idea that a human soul could be weighed intrigued many people, including a doctor named Duncan MacDougall of Haverhill, Mass. Not only would weighing the soul seemingly scientifically prove its existence, but it would empirically quantify its weight and perhaps answer a question that puzzled theologians for millennia.

In 1907 MacDougall devised an experiment to measure the soul, weighing six terminally ill patients before and after death. His results varied (and several of the measurements were thrown out as invalid), but in the end he concluded that there was indeed a very slight loss of weight, twenty-one grams on average. The announcement that MacDougall had measured the soul caused quite some controversy, and soon a closer look at his methods revealed fatal flaws. Without getting too morbid, there are several things that happen when a person dies that could potentially lead to a very slight decrease in the body’s weight, including the releasing of bowels and water loss respiration.

MacDougall used a very small sample size and his results were inconsistent. Scales were not correctly adjusted, one-third of the results were thrown out (leaving an untenably tiny sample size of four), one person died too quickly to be correctly measured and so on. Furthermore, because the quality and accuracy of medical devices was very crude in 1907, MacDougall was unable to accurately establish the precise moment of death. Sloppy science is nothing new, but in this case it spawned a weird, bogus factoid that remains widely believed over a century later.

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This is one of the classic, venerable, and fatally flawed (yet widely believed) bogus science statistics of all time. If they ever create a Museum of Spectacularly Skewed Statistics, this one will be the main attraction, behind velvet ropes and under gleaming spotlights.

Many people believe that some scientist somewhere calculated that we only use 10 percent of our brains. For some it implies that psychic powers must be real and simply the result of people who are able to somehow harness the other 90 percent of their brains that the rest of us don’t use. It’s not clear where exactly this amazingly flawed statistic comes from, but it’s not from neuroscience or modern medicine, which shows that we use all of our brains. Brain imaging research techniques such as PET scans (positron emission tomography) and fMRI (functional magnetic resonance imaging) clearly show that the vast majority of the brain does not lie unused, researchers have found.

In the book, “50 Great Myths of Popular Psychology,” psychologist Scott Lilienfeld explains: “The last century has witnessed the advent of increasingly sophisticated technologies for snooping in the brain’s traffic... Despite this detailed mapping, no quiet areas awaiting new assignments have emerged. In fact, even simple tasks generally require contributions of processing areas spread throughout virtually the whole brain.” In other words, you’re using all of your brain, like it or not.

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Parents already uneasy about the safety of the Internet and concerned about the Stranger Danger threat had their fears confirmed in the mid-2000s when a concerning statistic circulated widely in the news media claiming that a study found that one in five children is approached by an online predator. If 20 percent of American kids is really being approached by child molesters, given the amount of time the average kid spends online, this is clearly a very real and troubling threat.

Or at least it would be, if it were true. The “one in five statistic” can be traced back to a 2001 Department of Justice study issued by the National Center for Missing and Exploited Children (“The Youth Internet Safety Survey”) that asked 1,501 American teens between 10 and 17 about their online experiences. Among the study’s conclusions: “Almost one in five (19 percent)…received an unwanted sexual solicitation in the past year.” However, “sexual solicitation” was broadly defined as a “request to engage in sexual activities or sexual talk or give personal sexual information that were unwanted or, whether wanted or not, made by an adult.” Using this definition, one teen asking another teen if he or she is a virgin could be considered “sexual solicitation.”

Not a single one of the reported solicitations led to any actual sexual contact or assault. Furthermore, almost half of the “sexual solicitations” came not from “online predators” but from other teens -- in many cases the equivalent of teen flirting. As the study noted, “Much of the offending behavior comes from other youth (and) from females.” Of course online predators are a threat, but they are far less prevalent than this bogus statistic suggests.

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This statistic has been widely quoted for decades, and appears prominently in many feminist books. Gloria Steinem, in her 1993 book on women’s self-esteem, “Revolution from Within,” states that in America alone “about 150,000 females die of anorexia each year.” Steinem’s source for this statistic on the incidence of anorexia was not a published journal study, but instead another feminist book, Naomi Wolf’s 1991 best-seller “The Beauty Myth.” Wolf cites that statistic, and gives as her source a 1988 book, “Fasting Girls: The Emergence of Anorexia as a Modern Disease,” by Joan Jacobs Brumberg. Each writer repeated the statistic without checking its accuracy.

Writer Christina Hoff Sommers traced the origin of this flawed statistic to a misquoted newsletter from now-defunct eating disorder information group that referred to 150,000 anorexia sufferers, not 150,000 anorexia deaths. According to “The Handbook of Eating Disorders,” the most reliable estimates place the prevalence of anorexia nervosa at 0.3 percent for young females, with a crude mortality rate of between 4 percent and 5.9 percent.

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Always beware of precise-sounding statistics, especially when they are applied to the human body and all its glorious variation.

The much-revered 98.6 number is essentially a statistical average, not an accurate “normal” temperature for any given person under any given conditions. There is no single “normal” temperature for the human body; instead, body temperature is influenced by many factors, including what a person is doing and even by time of day: all else being equal, the human body has a lower temperature early in the morning and a higher one in the late afternoon. It also depends on what part of the body you measure; there is no one single correct temperature for the entire body, ranging from the heart to the skin.

In an otherwise healthy person, exercise can obviously influence the body’s temperature, but so can eating, drinking, pregnancy, the weather, and even emotional excitement such as arousal or embarrassment. The normal body temperature of babies, for example, varies considerably more than that of adults - partly because their hypothalamus, which helps control body temperature, is not fully developed.

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The claim that a third of gay teens kill themselves has been around for over a decade, but circulated widely in the wake of the suicide of Rutgers student Tyler Clementi in 2010. It makes sense on the face of it: gays and teenagers are both groups with higher risk for suicide than average. So gay teens, having two independent, elevated risk factors for suicide,- probably increases the likelihood. But does it increase it so much that fully 33 percent of gay teens kill themselves? That seems like an awfully high number.

Joel Best, professor and chair of sociology and criminal justice at the University of Delaware, debunked the statistics behind the gay teen suicide rate in his 2001 book “Damned Lies and Statistics.” Best noted that the one-in-three gay teen suicide statistic was derived from “a chain of bad statistics” using discredited and outdated numbers, dubious assumptions, math errors and arbitrarily selecting the highest numbers in estimates of suicide incidence.

So what is the gay teen suicide rate? No one knows, writes Best. “Coroners, after all, do not record sexual orientation on death certificates... . The final figure depends completely on the assumptions used to make the calculations.”

According to a study by Cornell University’s Ritch Savin-Williams published in the December 2001 Journal of Consulting and Clinical Psychology, “The assertion that sexual-minority youths as a class of individuals are at increased risk for suicide is not warranted."