Psychology & Science Module 2 PDF

2 Psychology MODULE & Science Photo Credit: © Firefly Productions/Corbis A. Answering Questions...

2 Psychology MODULE & Science Photo Credit: © Firefly Productions/Corbis A. Answering Questions 28 I. Application: Research Concerns 40 B. Surveys 29 Summary Test 42 C. Case Study 30 Critical Thinking 44 D. Cultural Diversity: Use of Placebos 31 Does Binge Drinking Cause Later Health Problems? E. Correlation 32 Links to Learning 45 F. Decisions about Doing Research 34 G. Scientific Method: Experiment 36 Concept Review 38 PowerStudy 4.5™ Complete Module H. Research Focus: ADHD Controversies 39 26  Introduction Blake’s Problem Perhaps the major questions surrounding the use of Ritalin When Blake was 3 years old, he crawled concern whether it is being overprescribed, whether it is What’s wrong into a T. rex display at a museum and the most effective treatment, and how long a child with with Blake’s set off blaring alarms. As a child, ADHD should remain on the drug (Root & Resnick, he was easily bored, couldn’t focus 2003). In addition, Ritalin, especially in larger doses, behavior? on anything for very long, and does have side effects that may include loss of appe- never sat still for more than a second. Blake admits that he tite and problems with sleeping. A related question gets easily bored and is often so desperate to find some- Image not is whether children with ADHD should be kept on thing interesting to do that he goes “full steam ahead avaliable a diet free of artificial dyes, sweeteners, and sugar, without thinking.” One day, to keep himself entertained, which some parents claim worsen the symptoms. he launched rockets (accidentally) into the neighbor’s We’ll answer these questions in this module. swimming pool! Blake’s mother describes him as “exhaust- We’re going to use Blake’s problem with ing” and “off the wall.” “Within minutes, he’d go from ADHD to show how researchers pursue the concocting baking-soda volcanoes to dumping out all the Blake, now a college four goals of psychology that we discussed in Lego and K’nex sets, to emptying out the linen closet in student, was diagnosed Module 1. In Blake’s case, the four goals are with ADHD at age 5. (1) to describe Blake’s symptoms, (2) to explain order to build a tent city,” says his mother (Taylor-Barnes, 2008) (adapted from B. E. S. Taylor, 2007). their causes, (3) to predict their occurrence, and At age 5, Blake was diagnosed with a behavioral problem that (4) to control Blake’s behavior through some behavioral therapy or has been surrounded with controversy. Blake was diagnosed as drug treatment. being hyperactive and inattentive, a problem that is officially called attention-deficit/hyperactivity disorder, or ADHD (American Centipedes and Cough Medicine Psychiatric Association, 2000). One interesting aspect of trying to control Attention-deficit/hyperactivity disorder, or ADHD, is not diagnosed by Can beliefs unwanted symptoms with a drug treatment any medical tests but on the basis of the occurrence of certain behavioral cure like real is that sometimes the drug is not really a problems. A child must have six or more symptoms of inattention, such as medicine? drug because it has no proven medical making careless mistakes in schoolwork, not following instructions, and effects. For example, in many parts of Asia, being easily distracted, and six or more symptoms of hyperactivity, such as people believe powdered tablets made from centipedes are medi- fidgeting, leaving classroom seat, and talking excessively. These symptoms cine for treating a variety of physical problems. Similarly, in the should have been present from an early age, persisted for at least six United States, people spend billions of dollars a year on over-the- months, and contributed to maladaptive development. counter cough medicines, One controversy surrounding ADHD involves diagnosis. Since including cough syrups ADHD is based not on medical tests but rather on the occurrence of and cough drops, even certain behavioral problems, how can parents and teachers distin- though there is no reli- guish children with ADHD from those who are naturally outgoing able scientific evidence and rambunctious (West et al., 2005)? Because of this difficulty, the t hat coug h med icat ions work American Academy of Pediatrics issued guidelines for diagnosing (J. W. Payne, 2006). The use of centipedes ADHD (AAP, 2000; M. Stein & Perrin, 2003). These guidelines and cough medicine, both questionable Can centipedes cure all stressed that, before the diagnosis of ADHD is made, a number medical treatments, raises the interesting kinds of problems? of the symptoms described above should be present for at least six question of how much one’s mind or months. The guidelines focused on children aged 6 to 12 because one’s beliefs contribute to the development or treatment of physical there isn’t sufficient evidence for making the diagnosis of ADHD at symptoms. We’ll discuss methods that researchers use to decide earlier ages. The goal of these guidelines is to prevent merely ram- whether the effectiveness of a treatment is due to a drug’s medical bunctious youngsters from being overmedicated while ensuring that effect or the person’s beliefs. children with ADHD get the help they need (Leslie et al., 2004). Another controversy is how to treat children with ADHD. To What’s Coming help control Blake’s ADHD, he was given a popular drug that is a Our main focus in this module is to explore the methods that relatively powerful stimulant, called Adderall. With the continued researchers use to answer questions, such as how to treat ADHD aid of medication, Blake has become a successful student at the and why placebos work. Specifically, we’ll discuss the advantages University of California at Berkeley and written his own memoir. and disadvantages of three major research methods—surveys, case Researchers do not completely understand why stimulant drugs, studies, and experiments. We’ll explain which research procedures such as Adderall or Ritalin, decrease activity in children. But drugs can identify cause-and-effect relationships and which cannot. We to treat ADHD are undeniably popular as spending on these medi- begin with an overview of the three major research methods that cations has reached $3 billion a year (M. Potter, 2006; Scrip, 2006). psychologists use to answer questions. INTRODUCTION 27 A. Answering Questions As you look at the photo of Blake neurological, cultural, and environmental factors (Barkley, How do on the right, you see a mature 2006). Finally, the most popular treatment of ADHD is researchers young adu lt. But, w it hout giving children a stimulant drug. study ADHD? medication, Blake has great In the middle of these controversies are parents like difficulty focusing: “A way you Blake’s mother, who, after dealing with a hyperactive can think about it is if you’re taking a TV remote and and impulsive child from an early age, have little doubt somebody else is just changing it uncontrollably and Image not ADHD exists and stimulant medication decreases your mind is floating from the History Channel to avaliable hyperactivity and impulsivity. At the same time, HBO to the Discovery Channel—it’s like you can’t critics warn that ADHD may be misdiagnosed or really stay concentrated” (B. E. S. Taylor, 2008). overdiagnosed and that, while stimulant medi- Twenty-five years ago, ADHD was a relatively cation may reduce activity, it fails to improve small problem in the United States, while today mental functions such as ignoring distractions it is the most commonly diagnosed behavioral and recalling information needed to reach a goal problem in children. The diagnosis of ADHD is (Coghill, 2007). not straightforward, since it is based on behavioral As researchers work to resolve the controversies symptoms rather than medical tests. The proposed Researchers use three different surrounding ADHD, they are using three research research methods to study ADHD. causes of ADHD are many, including genetic, methods—survey, case study, and experiment. Survey Case Study Experiment Suppose you wish to know how Suppose you wish to know in greater detail about how a Suppose you thought that sugar or many children have ADHD, single child, such as Blake, developed ADHD, performs artificial dyes caused hyperactivity in whether it occurs more in boys in school, makes friends, plays team sports, and deals your child and you wondered if this or girls, which treatment is the with everyday problems. Or suppose you wish to know were true. For example, based on case most popular, and how many about how a family copes with a child who has ADHD. studies and parents’ reports, one chi ldren continue to have For example, one mother said, “Ritalin doesn’t take away researcher thought that certain artifi- problems when they become the problems at all. It just helps him focus on what he’s cial dyes, chemicals, and sweeteners adults. Researchers obtain this doing. You can talk to him; he can get his school work increased the activity and impulsive information with surveys. done. It still takes him a long time to get things done. behavior of children diagnosed with A survey is a way to obtain He’s still behind, emotionally and socially” (San Diego A DHD (Feingold, 1975). W hen information by asking many indi- Tribune, November 27, 1989). When another mother was researchers want to identify a cause- viduals—either person to person, told that sugar doesn’t increase activity, she replied, “I say, and-ef fect relationship, such as by telephone, or by mail —to they’re nuts! Where were they last Christmas when my whether sugar increases activity, they answer a fixed set of questions sons ate candy canes and green frosting for days and never use an experiment. about particular subjects. slept!” (Los Angeles Times, February 9, 1994). Researchers An experiment is a method for identi- T he d i s a d v a nt a ge of a gather in-depth data about a particular individual with a fying cause-and-effect relationships by survey is that such informa- case study. following a set of rules and guidelines that tion can contain errors or be A case study is an in-depth analysis of the thoughts, feel- minimize the possibility of error, bias, and biased because people may not ings, beliefs, experiences, behaviors, or problems of a single chance occurrences. remember accurately or answer individual. A disadvantage of an experiment truthfully. The advantage of a One disadvantage of a case study is that its detailed is that information obtained in one survey is that it is an efficient information about a particular person, such as Blake, experimental situation or labora- way to obtain much informa- may not apply to other children with ADHD. tory setting may not apply to other tion from a large number of One advantage of a case study is that its detailed situations. An experiment’s primary people. information allows greater understanding of a particular advantage is that it has the greatest But if researchers wanted to person’s life. potential for identifying cause-and- know more about a particular But if researchers wanted to establish whether sugar effect relationships with less error person, they would use a case really increases activity in children with ADHD, they and bias than either surveys or case study. would use an experiment. studies. Very often, researchers use all three research methods—survey, case study, and experiment—because each provides Which method a different kind of information. Surveys provide information about fixed questions from a large number of people. is best? Case studies give in-depth information about a single person. Experiments point to cause-and-effect relationships. We’ll discuss the advantages and disadvantages of each of the three methods, beginning with surveys. 28 MODULE 2 PSYCHOLOGY & SCIENCE  B. Surveys Kind of Information Almost every day the media report some new survey. Although surveys tell us what others believe or how they What do behave, survey questions can be written to bias the answers; moreover, people may not always answer truthfully surveys tell us? (N. Schwartz, 1999). For example, how many people do you think always wash their hands after going to the bathroom? We’ll sample some surveys and then discuss their problems. Do you wash your hands? Do you multitask while driving? How many children are diagnosed with ADHD? Although 92% of the people A survey of Recent telephone surveys of parents report surveyed by telephone said they 1,503 drivers that 5% of U.S. children between 6 and 17 always washed their hands after found that years old are diagnosed with ADHD. Boys using a public bathroom, direct 72% say they are reported to be diagnosed with ADHD observation of 6,076 people in do other twice as often as girls. ADHD is reported four major cities things while to be more common among adolescents found that only 77% driving (use than younger children, and more com- really do and that cell phone, mon among White and African American more women drink, eat). children than Hispanic children (CDC, 2008c). (88%) washed The percentages of people in each age These examples show that surveys provide a great deal their hands group who multitask are 60% for of useful information. However, surveys have potential than men 16–17-year-olds, 78% for 18–30-year- problems with accuracy (as in the hand-washing survey) (66%) (ASM, olds, 80% for 31–44-year-olds, and and, as you’ll see next, with how questions are worded and 2007). 65% for 45–61-year-olds (NMI, 2008). who asks the questions. Disadvantages Advantages How questions are worded While guarding against error and bias, Photo Credits: left, © Jutta Klee/Getty Images; center, © Blend Images/SuperStock; right, © Image Source/Getty Images You may be surprised to learn that surveys may get very different results depending on surveys can be a useful research tool to how questions are worded. Here are two examples: quickly and efficiently collect information on behaviors, beliefs, experiences, and atti- QUESTION: “Would you say that QUESTION: “Would you say that tudes from a large sample of people and industry contributes more or less to traffic contributes more or less to can compare answers from various ethnic, air pollution than traffic?” air pollution than industry?” age, socioeconomic, and cultural groups. Traffic contributes more: 24% Traffic contributes more: 45% For example, surveys suggest that ADHD Industry contributes more: 57% Industry contributes more: 32% interferes with performance in school set- tings, decreases the chances of graduating These two examples indicate that the way questions are phrased and the way the possible from high school, and may lead to conduct answers are ordered can greatly influence people’s responses and, in this case, produce disorder problems in adolescence as well as opposite results (reported in U.S. News & World Report, Dec. 4, 1995, p. 55). continued problems in adulthood (Root & Resnick, 2003). Who asks the questions Because surveys indicate that children You may also be surprised to learn that the sex or race of the questioner can also affect with ADHD have major problems in how people answer the questions. school settings, psychologists are develop- ing methods for improving performance. QUESTION: “The problems faced by Blacks were brought on by Blacks These methods include: teaching ADHD themselves.” children how to organize their work, giving When the interviewer was White, 62% of Whites who were interviewed agreed. them constant feedback on reaching their When the interviewer was Black, 46% of Whites who were interviewed agreed. goals, and starting programs that train teachers and families to work together to These two examples indicate that when asked about sensitive or emotional issues, help ADHD children control their disrup- people take into account the race of the interviewer and tend to give socially acceptable tive behaviors (Hechtman et al., 2004). rather than honest answers (U.S. News & World Report, Dec. 4, 1995, p. 55). Thus, another advantage of surveys is their We can conclude that surveys can be biased because people may not answer questions ability to identify problems and evaluate truthfully, may give socially acceptable answers, or may feel pressured to answer in cer- treatment programs. tain ways. Also, surveys can be biased by how questions are worded and by interviewing However, if researchers wish to focus on a group of people who do not represent the general population (Gravetter & Forzano, a particular individual rather than a group, 2009; S. J. Jackson, 2009). Despite these potential problems, surveys have advantages. they use a case study. B. SURVEYS 29 C. Case Study Kind of Information Sometimes researchers answer (left image). In it, he discusses the challenges he What’s a questions by studying a single faced from early childhood through the present. He case study? individua l in great detail, talks about how he must take his ADHD medica- which is called a case study. tion, keep a daily routine, and make sure to get 9 A case study is an in-depth analysis of the thoughts, hours of sleep at night to keep his ADHD symptoms feelings, beliefs, or behaviors of a single person. Image not from getting out of control. As a result of his moti- We’ve been discussing the case of Blake Taylor avaliable vation and self-discipline, Blake enjoys a balanced throughout the module. From the age of 3, Blake college life spent studying, working out, playing has had problems paying attention and complet- music, socializing, volunteering, and, of course, ing tasks. Throughout his childhood, he felt no getting enough sleep (Anwar, 2008; B. E. S. Taylor, one understood the challenges he endured. To help 2007). Sometimes case studies help answer ques- others understand what it’s like to live with ADHD, tions, but case studies can also result in wrong or he wrote his autobiography called ADHD & Me biased answers. Personal Case Study: Testimonial Observations from case studies may be mis- recently, there are testimonials from parents that children with Why did interpreted if the observer has preconceived attention-deficit disorder who ate foods with an artificial sweetener, parents make notions of what to look for. For aspartame (Nutrasweet), showed noticeable Average Ratings of Child Behaviors a mistake? example, beginning in the mid- and Cognitive Functions increases in symptoms. 1970s, parents were told that To test the accuracy of these recent food with artificial additives, dyes, and preservatives Placebo 13.5 testimonials, researchers asked teachers could cause hyperactivity in children (Feingold, and parents to evaluate the behaviors and 1975). Shortly after, parents reported that, yes indeed, cognitive functions of children who were Aspartame 13 artificial additives caused a sudden increase in rest- given a capsule containing either ten times lessness and irritability in their hyperactive children their normal daily intake of aspartame or a (Feingold, 1975). The parents’ reports and beliefs that additives placebo. Neither parent, child, nor teacher knew if the capsule con- cause hyperactivity are examples of another kind of case study, tained aspartame or the placebo. As the graph on the left shows, called a testimonial. there was little or no difference between the effect of aspartame A testimonial is a statement in support of a particular viewpoint based (Nutrasweet) and that of the placebo on the behaviors or cognitive on detailed observations of a person’s own personal experience. functions of children with attention-deficit disorder (B. A. Shay- However, contrary to the parents’ testimonials, researchers have witz et al., 1994). Although testimonials from parents, friends, or generally found that amounts of artificial additives within a nor- peers can be very convincing, we’ll point out two problems that mal range did not affect hyperactivity (Kinsbourne, 1994). More make testimonials especially susceptible to error. Error and Bias One of the major problems with testimonials is that they are based on our personal observations, which What’s the problem have great potential for error and bias. For example, if parents reported that sweeteners increased their son’s with testimonials? activity, we would have to rule out personal beliefs and self-fulfilling prophecies. Personal beliefs. If parents hear that Self-fulfilling prophecy. If parents believe that artificial sweeteners cause problems, artificial sweeteners may cause physi- they may behave in ways—being more strict or less sympathetic—that cause the problems cal or psychological problems, they may to occur. This phenomenon is called a self-fulfilling prophecy. interpret their child’s problems as caused A self-fulfilling prophecy involves having a strong belief or making a statement (prophecy) about by artificial sweeteners. Because of biased a future behavior and then acting, usually unknowingly, to fulfill or carry out the behavior. perceptions, parents may overlook If we strongly believe that something is going to happen, we may unknow- other potential causes, such as frus- ingly behave in such a way as to make it happen (R. Rosenthal, 2003). Self-ful- tration, anger, or changes in the filling prophecies reinforce testimonials and thus keep our biased beliefs alive. child’s environment, and make the The main disadvantage of testimonials is their high potential for error and error of focusing only on artificial bias. But they have the advantage of providing detailed information that may sweeteners. If we believe strongly point to potential answers or lead to future studies. We’ll discuss how case in something, it may bias our Parents mistakenly studies are used in developmental research in Module 18 and clinical research perception and cause us to credit believed that in Module 21. an unrelated treatment or event artificial sweeteners Next, we’ll discuss how testimonials are a popular source of information, caused ADHD. as the reason for some change. especially when we are talking about placebos. 30 MODULE 2 PSYCHOLOGY & SCIENCE  D. Cultural Diversity: Use of Placebos Examples of Mind over Body Psychologists are interested in how the mind gastric ref lux, high blood pressure, headaches) (Begley, 2008b; Have you influences the body, such as happens when some- Christensen, 2001). Because placebos can be effective in treating taken a one takes a pill that happens to be a placebo. different problems, almost 50% of U.S. doctors prescribe placebos placebo? A placebo is some intervention, such as taking a to their patients (Steenhuysen, 2008a). pill, receiving an injection, or undergoing an You may be wondering how it is that placebos can operation, that resembles medical therapy but that, in fact, has no be so effective. Placebos may work because beliefs and medical effects. thoughts are powerful enough to produce the same A placebo effect is a change in the patient’s illness that is relief provided by real drugs (Ariely, 2008; Kluger, attributable to an imagined treatment rather than to a medical 2009). For instance, researchers in one study injected treatment. subjects with a pain-inducing solution and then falsely For example, the results of a study involving children told subjects they had been injected with pain-reliev- who were depressed showed that an antidepressant medi- ing medication (placebo). Pictures of subjects’ brains cation decreased depression in 69% of children. However, were then taken (PET, p. 71), and results showed that 59% of the children reported equally good results from for those people who said they felt less pain, their taking a placebo (a sugar pill) (Saxbe, 2004). In fact, many brain released natural painkillers after the placebo The power of placebos similar studies have reported a placebo to be just as effec- is in the mind. was injected (Haslinger, 2005). Our beliefs can actu- tive as antidepressant medication (R. Rubin, 2008). ally change what is happening in our brain! Researchers estimate that between 35% and 75% of patients ben- As you’ll see, testimonials from around the world claim that efit from placebos for various problems (pain, depression, asthma, different kinds of placebos can cure a wide variety of symptoms. Rhino Horn Centipedes Tiger Bones Cough Medication Millions of people in China, Tai- In parts of Asia, a popular There has been a massive When we have a cold wan, Thailand, and South Korea “medicine” to treat many kinds decline of tigers in Asia with a relentless cough, Photo Credits: top, © Andy Ryan/Getty Images; bottom left, © DLILLC/Corbis; bottom center, © Photodisc/Getty Images claim rhino horn will increase of physical problems is a tablet because tiger bones are used many of us purchase their sexual desire and stamina and made from the Korean centipede. to treat ulcers, typhoid, cough syrup. In the will cure everything from head- It is believed to cure arthritis, malaria, joint pain, and United States, billions aches and nosebleeds to fevers and kidney stones, malaria, skin burns; to increase longevity; of dollars are typhoid. A single rhino horn diseases, and severe scars. Folk to improve sexual desire; spent every weighing 4 to 5 pounds will bring and to cure devil possession year on as much as $50,000 on the black (Friend, 1997; T. Sylvester, cough market. Because of the high 2009). In addition, wealthy medica- demand for rhino horns, Taiwanese pay $320 for a tions the number of bowl of tiger penis soup that (cough rhinos in Asia logic seems to guide the use of is thought to increase flag- syrups has sharply centipedes as “medicine.” For ging libidos (Nagarahole, and loz- declined (Berger instance, centipedes have many 1994). Tiger bones and tiger enges), yet & Cunningham, legs and are used to treat leg penises func- there is no 1994). Despite the problems (Pemberton, 2005; tion as power- scientific evidence that healing claims of rhino horn, its SACU, 2001). In fact, centipede ful placebos these over-the-counter basic ingredient is compacted hair poison may cause pain, nausea, in traditional medications work (keratin), which has no proven and fatal cases of organ failure Asian (Ignelzi, 2006a; J. W. medicinal powers (Sierra, 1989). (Norris, 2008; Yuen et al., 2006). medicine. Payne, 2006). Conclusion: Testimonials and Placebos The main reason placebos are used worldwide, even to the point of destroying certain wild animals, is that the placebos’ Why are beneficial “medical” effects are supported by countless testimonials. For example, compared to the results of surveys, placebos so testimonials are much more convincing because they are based on real-life experiences of friends, peers, and parents, popular? who are honest and believable. However, it is common for people, honest and trustworthy, to unknowingly make a mistake and conclude a rhino horn, centipede, tiger bone, or cough medication is producing a beneficial “medical” effect when the beneficial effect is actually being caused by the individual’s mental thoughts influencing the brain or body’s functioning (Ariely, 2008). As you’ll see next, people often make mistakes about the effect of placebos because there is often no way to figure out what causes what. D. CU LT U R A L DI V E R S I T Y: U S E O F P L ACE B O S 31 E. Correlation Definition The photo on the left shows a A correlation is an association or relationship in What’s a boy running wild in a super- the occurrence of two or more events. correlation? market. Researchers would like For example, if one twin has hyperactivity, to know if this boy’s hyperactiv- a correlation will tell us the likelihood that the ity has a genetic basis. One way to identify genetic other twin also has hyperactivity. The likelihood factors is to study identical twins because they share or strength of a relationship between two events almost 100% of their genes. Suppose you were study- is called a correlation coefficient. ing the occurrence of ADHD in identical male twins A correlation coefficient is a number that indicates and found that about 75% of the time, if one identical the strength of a relationship between two or more twin had ADHD so did the second twin (Faraone et events: the closer the number is to –1.00 or +1.00, the al., 2005). This strong relationship between behaviors greater is the strength of the relationship. Research suggests that ADHD has a genetic basis. in identical twins suggests a genetic basis for ADHD. We’ll explain correlation coefficients in more Such a relationship is called a correlation. detail because they can be confusing. Correlation Coefficients What are If each of 20 identical pairs showed equal levels of hyperactivity, the correlation coefficient would be positive and perfect and would be indicated by a +1.00 correlation coefficient. these numbers? A perfect positive correlation coefficient of +1.00 means that an increase in one event is always matched by an equal increase in a second event. For example, if one identical twin has hyperactivity, There are two major then the other twin always has hyperactivity. A correlation of +1.00 is virtually never found in applied points to understand psychological research (Hemphill, 2003). about correlations: First, a correlation means there is an If some identical pairs but not all 20 pairs were similar in hyperactivity, the result would be a positive association between correlation coefficient, which can range from +0.01 to +0.99. two or more events. A positive correlation coefficient indicates that as one event tends to increase, the second event For example, there is tends to, but does not always, increase. an association, or cor- As the coefficient increases from +0.01 to +0.99, it indicates a strengthening of the relationship relation, between the between the occurrence of two events. sex of a child and the occurrence of ADHD; If one twin of 20 pairs showed hyperactivity while the other twin sometimes did and sometimes did four to five times more not show hyperactivity, the result would be no association, or zero correlation (0.00). boys are diagnosed A zero correlation indicates that there is no relationship between the occurrence of one event and with ADHD than girls. the occurrence of a second event. A second point to understand about correlations is that the If, in some identical pairs, one twin showed an increase while the other showed an equivalent strength of the rela- decrease in activity, the result would be a negative correlation coefficient, which can range from Photo Credit: top, © Jose Azel/Aurora Quanta Productions tionship or association −0.01 to −0.99. is measured by a num- A negative correlation coefficient indicates that as one event tends to increase, the second ber called a correlation event tends to, but does not always, decrease. coefficient. Because the As the coefficient increases in absolute magnitude from −0.01 to −0.99, it indicates a strengthening correlation coefficient in the relationship of one event increasing and the other decreasing. ranges from +1.00 to –1.00, its meaning can If one twin of 20 identical pairs showed hyperactivity and the second twin always showed decreased be confusing. In the activity, the correlation coefficient would be negative and perfect and would be indicated by a −1.00 boxes on the right, correlation coefficient. we’ll describe what A perfect negative correlation coefficient of −1.00 means that an increase in one event is always correlation coefficients matched by an equal decrease in a second event. For example, if one identical twin has hyperactivity, mean, beginning at then the other twin always has decreased activity. A correlation of −1.00 is virtually never found in the top of the scale applied psychological research (Hemphill, 2003). with a +1.00. 32 MODULE 2 PSYCHOLOGY & SCIENCE  The media often headline interesting between two events, such as thinness and length of life, Can you findings: Thin people live longer than then it’s a correlation. In fact, all three findings reported recognize a heavier ones; overweight people earn here are correlations. The reason you should check correlation? less money than their peers; wearing whether some finding is a correlation is that correla- school uniforms decreases violence. tions have one very important limitation: They do not Before you assume that one event causes the other, such as identify what causes what. For example, let’s look thinness causing one to live longer, you must check to see what closely at findings about breast feeding and intelligence researchers did. If researchers measured only the relationship test scores. Correlation Versus Causation The biggest mistake people make in discussing correlations is Breast Feeding and Adult Intelligence Test Scores assuming that they show cause and effect. For instance, many par- ents have been told that breast feeding their infant leads to greater 7–9 Months 106.0% intelligence. The graph on the right shows that duration of breast feeding was correlated with higher intelligence test scores during 4–6 Months 102.3% adulthood. Since an increase in the duration of breast feeding was associated with higher intelligence test scores, this is a positive 2–3 Months 101.7% correlation (Mortensen et al., 2002). Although the correlation between breast