By U. Cyrus. Winona State University. 2018.
This means that in the population of my typing order imipramine 75 mg free shipping, typos occur with a relative frequency of buy discount imipramine 25mg line. This expected relative frequency is expressed as a probability: the probability is discount 25 mg imipramine visa. If event A has a relative fre- quency of zero in a particular situation, then the probability of event A is zero. This means that we do not expect A to occur in this situation because it never does. At the most extreme, an event’s relative frequency can be 1: It is 100% of the population, so its probability is 1. This means that the relative frequencies of all events must add up to 1, so the probabilities must also add up to 1. Understand that except when p equals either 0 or 1, it is up to chance whether a partic- ular sample contains the event. For example, even though I make typos 80% of the time, I may go for quite a while without making one. People who fail to understand that probability implies over the long run fall victim to the “gambler’s fallacy. The fallacy is thinking that a head is now less likely to occur because it’s already occurred too often (as if the coin says, “Hold it. The mistake of the gambler’s fallacy is failing to recognize that whether an event occurs or not in a sample does not alter its probability because probability is deter- mined by what happens “over the long run. When we know the relative frequency of all events, we have a probability distribution. A probability distribution indicates the probability of all events in a population. Creating Probability Distributions We have two ways to create a probability distribution. One way is to observe the rela- tive frequency of the events, creating an empirical probability distribution. Typically, we cannot observe the entire population, so we observe samples from the population. We assume that the relative frequencies in the samples represent the relative frequen- cies in the population. Because his cranky days plus his noncranky days constitute all possibilities here, we have the complete probability distribution for his crankiness. Statistical procedures usually rely on the other way to create a probability distribu- tion. A theoretical probability distribution is a theoretical model of the relative frequen- cies of events in a population, based on how we assume nature distributes the events. From such a model, we determine the expected relative frequency of each event, which is then the probability of each event. For example, when tossing a coin, we assume that nature has no bias toward heads or tails, so over the long run we expect the relative frequency of heads to be. Because relative frequency in the population is probability, we have a theoretical probability distribution for coin tosses: The probabil- ity of a head on any toss is p 5. Therefore, the probability of you drawing any partic- ular card from a full deck is 1>52 5. Likewise, with 4 “Kings” in a full deck, the probability of you selecting one is 4>52 5. Finally, if the numbers you select for your state’s lottery drawing have a 1 in 17 million chance of winning, it’s because there are 17 million different possible combinations of numbers to select from. Therefore, we’ll draw your selection at a rate of once out of every 17 million draws, so your chance of winning on today’s draw is 1 in 17 million. First, we either theoretically or empirically devise a model of the expected relative frequency of each event in the population. Then, an event’s relative frequency equals its probability (our confidence) that it will occur in a particular sample. Factors Affecting the Probability of an Event Not all random events are the same, and their characteristics influence their probability. Two events are independent events when the probability of one is not influenced by the occurrence of the other. Obtaining Probability from the Standard Normal Curve 189 For example, contrary to popular belief, washing your car does not make it rain. These are independent events, so the probability of rain does not change when you wash your car. On the other hand, two events are dependent events when the probability of one is influenced by the occurrence of the other. For example, whether you pass an exam usu- ally depends on whether you study: The probability of passing increases or decreases depending on whether studying occurs. When sampling with replacement, any previously selected individuals or events are replaced back into the population before drawing additional ones. Sampling with replacement occurs if, after drawing the first card, we return it to the deck before drawing the second card. Notice that the probabilities on each draw are based on 52 possible outcomes, and so they stay con- stant. On the other hand, when sampling without replacement, previously selected individuals or events are not replaced into the population before selecting again. Thus, sampling without replacement occurs if, after a card is drawn, it is discarded. Now the probability of selecting a particular card on the first draw is based on 52 possible out- comes, but the probability of selecting a card on the second draw is different because it is based on only 51 outcomes. The probability of any event equals its ____ in ■ A probability distribution indicates all probabilities the ____. As the p of an event decreases, the event’s relative events are independent or dependent and whether frequency in this situation ____. Tossing a coin (heads or tails) is sampling ____ One hundred raffle tickets are sold each week. Assuming that all tickets are equally likely to be Answers drawn, each should be selected at a rate of 1 out of 1. For our discussions, pretend that we’ve already measured everyone’s score in a particular situation so that we can randomly select directly from the population of scores. Further, we will assume that scores are independent (whether someone else scores high on a test does not influence the p that you’ll score high) and sampled with replacement (the selection of a particular score does not remove it from the population). Then our theoretical probability distribution is usually based on the standard normal curve. This proportion corresponds to the relative frequency of the scores in that part of the population. Now, however, you know that the relative frequency of scores in the population is their probability.
Kondo4 intravenous immunoglobuline treatment and 2 weeks of inpatient 1International University of Health and Welfare Hospital order imipramine 25 mg mastercard, Rehabili- rehabilitation therapy buy discount imipramine 75 mg, fascial paralysis was improved purchase 50mg imipramine visa, dysphasia tation Medicine, Nasushiobara, Japan, 2Fujita Health University and dysarthria were recovered and, he was discharged to home with School of Health Sciences, Faculty of Rehabilitation, Toyoake, Ja- functional independence measurement motor subscore of 68/91 pan, 3Nagoya University Graduate School of Medicine, Preventive and he was ambulatory with a cane. The questionnaires were administered in one of tralia, Australian Catholic University, Faculty of Health Sciences, three modes: by self-report (mail), self-report (participant present at Melbourne, Australia the clinic), face-to-face interview. Signifcant morbidity can be observed articles, extracted data, assessed study methodological quality and at the site of this formation of new bone, including pain and loss rated the clinimetric properties and clinical utility. Conclusion: Although preliminary; our re- 1Fujita Health University, School of Health Sciences, Toyoake, Ja- sults indicate that screening all admissions may not be necessary. Results: Average ing cognitive emotional disorder, attention defcit, memory loss, score (21. Especially, it was exhibited that female changed results showed that the patient was in a low arousal state, and had “traditional” roles expected to perform (like housework) in Japa- attention defcit, memory loss, executive and intellectual dysfunc- nese community. The most frequent non traumatic factors are spinal stenosis, tumors, and infections. Ischemic myelopathy is Zhen Feng, Xiao-yang Dong a disorder characterized by acute-onset, fask or spastic quadripare- Department of Rehabilitation Medicine, the First Affliated Hos- sis or paraparesis and is a rare cause of paraplegia. Conclusion:Our fnding suggested that vagus nerve stim- ruled out such as fecal impaction. Subsequently, his blood pressure ulation could promote consciousness recovery in traumatic brain decreased and the symptoms disappeared immediately. The patient tolerated the procedure well volved in consciousness-promoting effects. Yılmaz1 ischemia occurs in the lower thoracic and upper lumbar section of 1Gülhane Military Medical Academy, Deparment of Physical Med- the spinal cord which is fed by the Adamkiewicz artery. Material and Methods: A 75-year- Kırıkkale, Turkey old male patient referred to our clinic with complaints of diffculty in walking and sensory loss. Though the etiology is un- There was no ischemic damage in cranial magnetic resonance im- clear, trauma is one of the causative factors. Material and Methods: A 45-year-old paraplegic male arrest related hypoxic ischemic spinal cord damage was considered. Laboratory stud- Gil Agudo1 ies and plain x-ray examination showed no abnormality. Doppler 1 ultrasonography showed 8,5x50 mm hematoma between muscle Hospital Nacional de Paraplejicos, Physical Medicine and Re- habilitation, Toledo, Spain, 2Hospital Nuestra Señora del Prado, groups. Two days later, resolution of the hematoma was recog- Introduction/Background: Surgical decompression of spinal canal nized below the skin and swelling began to relieve. C-reactive protein ated complications and functional results in patients that suffered a was elevated to 50. Material and Methods: tion revealed a large ossifcation at left that was not seen on previ- Descriptive and retrospective study on adult patients diagnosed ous x-ray. After a physical treatment program, six patients 1 showed neurological improvement. In all the cases, complications Gülhane Military Medical Academy, Department of Physical have been reported; urinary tract infection was the most frequent Medicine and Rehabilitation- Turkish Armed Forces Rehabilitation one. Gil from the right elbow because of range of motion limitation a year 1 Agudo ago. Shoulder, elbow, wrist, and hip were limited bilaterally from 1 place to place more than 50%. No signifcant swelling or redness Hospital Nacional de Paraplejicos, Physical Medicine and Re- habilitation, Toledo, Spain, 2Hospital Nuestra Señora del Prado, was observed and the patient had no pain. Even he had good muscle strength in Orthopedic Surgery, Talavera de la Reina, Spain lower extremities, the joint limitations interfered with ambulation Introduction/Background: Major trauma during pregnancy is the of the patient due to poor balance. He was also dependent on his all cause of 15% of mother mortality among non-obstetric reasons. Demographic characteristics, lesion type and complica- of spinal cord injury in physical medicine and rehabilitation prac- tions have been reported. Respiratory insuffciency and hemodinamical instability 2013, and for data analysis and raw prevalences were calculated jeopardize mother and fetus life, and after neurogenic shock, auto- with the corresponding specifc standard error level. Baquero Sastre1 medical condition where the anterior spinal artery, the primary 1Manuela Beltran University, Physical Therapy, Bogotá, Colombia blood supply to the anterior portion of the spinal cord, is inter- rupted, causing ischemia or infarction of the spinal cord in the Introduction/Background: The medular lesions are events whit high anterior two-thirds of the spinal cord. The syndrome has charac- frequency in the neurological pathologies, and their impacts have teristic symptoms that consist of sudden onset of faccid quadri- important effects in sensitive and motor elements related functional paresis with pain, dissociated sensory loss below the level of the movements affecting the possibilities of performance of individuals, lesion, and bladder dysfunction. It occurs most frequently in the and levels of quality of life, with large economic costs for rehabili- watershed zones, such as the midthoracic region (T3-T8). Material and causes of the syndrome reportedly include arteriosclerosis, infec- Methods: Developed a cross-sectional study with patients treated by tion, vasculitis, embolic events, sickle cell anemia, cervical cord neurological and particularly medular lesions in one Physiotherapy herniation, surgery and trauma. Treatment is determined based on Center of a Public Hospital of High Complexity in Bogota, between the primary cause of anterior cord syndrome. Material and Meth- the months of Feb to Sep 2013, the selection mechanism of the pop- ods: Case: A 70-year-old man with a 15-year history of diabetes ulation was a census of all elderly subjects 18 years old treated for mellitus and hypertension experienced pain and paresthesia in his neurological and medular lesions, and was calculated to analyze the lower limbs bilaterally. The pain suddenly increased, and following information raw and specifc prevalences with a level of standard er- the pain bilateral weakness of the lower limbs developed suddenly. Acute transverse myelitis, spinal ly with traumatic nature that surpass infectious, and oncological, cord compression, and demyelinating disorders may cause similar primarily affecting people of masculine gender. Therefore, this study aims to presence of trauma and violence the occurrence of these lesions determine demographic variables, clinical symptoms and perceived tend to have an increased frequency. Results: Majority of the patients emphasis to the emotional aspects and the impact on quality of life were young and less than 40 years old (66. Neurogenic bladders were managed by catheteriza- a clinical and functional examination was conducted and question- tion (77. Among troubles cit- Most patients had adequate support, managed to adapt to their ill- ies; an erectile dysfunction in 9 cases, a problem of ejaculation (slob- ness and not depressed. Aydemir2 was to identify QoL of subjects presenting with residual neurologi- cal defcits from a spinal cord injury and living at home. After informed consent was obtained, a clini- partment of Physical Therapy and Rehabilitation, Ankara, Turkey cal examination was conducted and questionnaires were flled out by the subjects. Results: The mean age was to evaluate the effectiveness of this protocol in tetraplegic patients. The evaluation was performed after on average of ing respiratory assessment and management themes was developed 3 years. Conclusion: In recent years, the focus of rehabilitation patients successfully weaned from mechanical ventilator and 30 of outcomes has shifted from the illness itself to a broader picture of 35 patients were decannulated. Four patients referred for diaphragm well-being; QoL is an important measure of the success of reha- pace stimulation and tracheal stenosis surgery. The majority of the the pattern of change in severity of involuntary movements as the lesions were at the thoracic level (58. Surgical stabilization of the spine was performed in 50 disorders presenting with a change in the nature of chorea in patients patients (49%). Some purposeful movement was regained but there 513 was also increasingly forid chorea and dystonia in her face, neck and shoulders.
When indicated order imipramine 75mg with mastercard, dentists be employed as anti-inflammatory agents (Graves et al cheap 25 mg imipramine fast delivery, should be checking hemoglobin A1c discount 25mg imipramine with amex. Periodontal dis- 1998), and, in the case of diabetes-associated periodon- eases are the sixth complication of diabetes mellitus. Advances in treatment of periodontitis will focus If, in the near future, multicentered, randomized, on procedures to induce regeneration of lost peri- controlled clinical trials confirm that periodontal odontal tissues. Among the specific mediators being disease causes systemic conditions, several issues studied for application in periodontal therapy are will confront the dental profession: recombinant bone morphogenetic proteins and combinations of growth factors. The success of x Studies will need to be conducted to determine these therapies will depend on the identification of the effectiveness of screening patients in the dental the appropriate biological mediator and the appro- office for certain diseases with obvious ramifications priate delivery system. If effective, these pro- grams will enhance the oral health and general Although there are a few negative findings (Hujoel health status of patients. Oral infections are suspected to be a risk lic and physicians that dentistry can no longer be factor for certain systemic diseases (that is, cardiovas- considered solely a luxury, elective health care. Increased x The recognition of the medical necessity for peri- communication by dentists with other health care odontal care will increase the perceived impor- professionals can be expected. Thus, the larger problems are strating a systemic therapeutic benefit from peri- the perception among health care professionals, the odontal therapy, there is no concrete evidence to jus- nature and system by which health care is delivered, tify a change in oral health care policy or current and access and utilization. Future research in humans should more demiological, basic science, social science and clinical thoroughly evaluate the maternal genotype in addition to trial research will enable them to participate more that of the fetus in determining risk of this birth defect. Current research efforts are point- ing the way to promising directions, especially in the x Continued efforts should target the identification areas of etiology/prevention and outcomes. Basic research should also work towards obtaining a x Family studies have for many years demonstrated better understanding of the molecular pathways that inherited genetic variation has a very large effect on that are disrupted by mutations at these genes. This will move us towards an era of genetics, promise to reveal their basic causes with "individualized medicine" where risk of orofacial continued investment. However, the nature of clini- clefting can be much more accurately predicted cal research requires very long-term commitments based on the "genetic blueprint" of the parents. The of major resources for patient recruitment and eval- human genome project has now produced the uation, laboratory assays, and data management tools and knowledge in the form of millions of single and statistical analysis. Groups around the world cur- tective dietary factors such as vitamins and folate rently focused on this research effort will need con- are needed to better understand the role of envi- tinued support for many years to achieve major suc- ronmental factors in both nonsyndromic and some cess. Clinical trials of new means of prevention for forms of syndromic orofacial clefting. Some recent research and initia- up a network of nearly all cleft/craniofacial teams in tives have begun to address these issues and can be used Europe to establish standards for recording and as guidelines for planning future directions. Dental specialists have played a major attempts to comprehensively compare treatment role in the creation of this organization. As with the outcomes from different centers, each with widely Craniofacial Outcomes Registry, the Eurocleft Project differing treatment protocols. Using multidiscipli- has the potential for providing collective information nary outcome measures and strict research method- on cleft/craniofacial treatment outcomes which will ology, these studies not only demonstrated the fact enable more productive future research efforts to iden- that outcomes can vary considerably based on the tify the most effective treatment regimes. Europe indicated that there were 194 different These long-term research efforts need to receive primary surgical protocols. Few randomized control trials have been car- ried out in the cleft/craniofacial field, and these are As a result of these developments, the potential essential in order to objectively determine the rela- future impact of the dental profession on improve- tive merits of different treatment methods. Since many of the projects moving results of treatment has led to several recent towards globalization of the research effort are still initiatives having the potential to greatly facilitate early in planning stages, dental professionals have a future outcomes research. For example, the great opportunity to shape these efforts to ensure Craniofacial Outcomes Registry is an attempt to that dental concerns in cleft/craniofacial care are establish standard outcome measures for all properly addressed. Appropriate training of dental aspects of cleft care, and to provide a centralized scientists in the execution of valid and reliable out- repository where individual cleft/craniofacial centers come studies and randomized control trials will can register patients online and then subsequently facilitate the development and use of evidence-based submit treatment information and out-come meas- treatment decisions by future cleft/craniofacial ures. Future research of a high caliber should final- making significant contributions to this effort, both ly allow for the scientifically-based elimination of in terms of participation in the establishment of valid treatment methods which fail to produce outcomes and reliable outcome measures, and also through and benefits necessary to justify their continued use. Finally, there is also a need clusion, such as osteodistraction and implant/ onplant- for the development of outcome measures which based anchorage, arise from basic research in biomate- incorporate the potentially more meaningful issues rials/bioengineering/biomimetics. In the future, a com- of patient/parent expectations, satisfaction, and bination of biological and biomechanical signals may quality of life evaluations (e. Furthermore, it should be advantageous to induce tooth development Research on human genetic variation that influ- in areas of tooth agenesis (Nuckolls et al, 1999). As ences the development of the craniofacial complex more is learned about cell biology and tooth move- may be one way to bridge the gap between develop- ment, the effect of different biomechanics may be stud- mental biology and the study of clinical variation. Understanding the genetic basis for malocclusion Nanotechnology and materials science may lead represents one of the major challenges for the to ways to generate biomechanical forces in a more future. Furthermore, there is a need to understand controlled and biologically appropriate manner. Retrospective/prospective investigations Research using both cell and tissue culture and (Johnston, 1998a,b) or randomized clinical trials animal models will greatly increase our knowledge (Ghafari et al, 1998) may be employed. The power of the process of cellular control, suture biology, of these investigations will increase with better com- genetic factors, and the interaction of environmental munication and interactions among centers pursu- factors with genetic susceptibility. Furthermore, advances in bioin- be to apply the increasing knowledge of craniofacial formatics may im-prove the reliability of predicting developmental biology (Thesleff, 1998) to research treatment outcomes. While treatment of major malocclusions will remain Investigators must also evaluate epigenetic factors in the domain of the orthodontic specialist, general that may activate expression of regulatory genes and practitioners will have an expanding role in the early influence postnatal growth (Carlson, 1999). In the future, sitive and non-invasive early oral cancer detec- new saliva-based diagnostic approaches based on the tion (Fliss et al, 2000). These algorithms will combine the development from oralleukoplakias (SudbØ et al, effects of environmental and genetic risk factors. Chemoprevention research is aimed at reversing the x New treatment approaches using gene therapy growth of advanced premalignant lesions using combined with chemotherapies (Khuri et al, retinoic acid derivatives and other substances (Geyer 2000), immunotherapy (Chikamatsu et al, 1999) et al, 1998). This approach may also help prevent and approaches directed at reducing invasiveness new primary cancers in patients who already have (Simon et al, 1999). Additional basic research and excess morbidity and mortality from causes other clinical trials are needed to evaluate promising chemo- than due to oral cancer itself, mostly due to the prevention approaches more rapidly and effectively. Since such individuals are at very substantially elevat- ed risk of developing oral cancer, they could be prior- x Developing more effective methods to educate itized for frequent oral examinations for early cancer dental professionals about oral cancer risk factors detection and for smoking and alcohol cessation inter- and to encourage high quality and frequent oral vention programs (Prochazka, 2000). The resulting reduction in salivary genetic assessments, in combination with alcohol, flow will result in an increased incidence of fungal, tobacco and dietary risk-factor profiles, to more viral and less common bacterial infections. Such risk determinants can guide the clinician in preventive strategies or treatment decisions. The use of polymerase chain reaction several million human single nucleotide polymorphisms techniques has made it possible to study the potential and strategies to relate these genes to disease risk relationship of bacteria to aphthous stomatitis at the (Chakravarti, 2001; and Peltonen and McKusick, molecular level. In addition to greatly facilitating the identifica- tion between Helicobacter pylori and aphthous stom- tion of genes most strongly associated with oral cancer atitis. If true, this finding might suggest a reason why risk, these tools will also usher in an exciting new era of clinicians have long reported the response of canker individualized risk assessment and therapy.
For example discount imipramine 50mg on line, treat- ment status deﬁned as whether participants receive the active drug treatment or inactive treatment (placebo) is an independent variable generic 75 mg imipramine. A common error in statistical analyses is to misclassify the outcome variable as an explanatory variable or to misclassify an intervening variable as an explanatory variable generic 75 mg imipramine with mastercard. It is important that an intervening variable, which links the explanatory and outcome 8 Chapter 1 Table 1. For example, hay fever cannot be treated as an independent risk factor for asthma because it is a symptom that is a consequence of the same allergic developmental pathway. In a case–control study in which disease status is used as the selection criterion, the explanatory variable will be the presence or absence of disease and the outcome variable will be the exposure. However, in most other observational and experimental studies such as clinical trials, cross-sectional and cohort studies, the disease will be the outcome and the exposure or the experimental group will be an explanatory variable. In hypothesis testing, a ‘null hypothesis’ is ﬁrst speciﬁed, that is a hypothesis stating that there is no difference, for example, there is no difference in the summary statistics of the study groups (placebo and treatment). The null hypothesis assumes that the groups that are being compared are drawn from the same population. An alternative hypothesis, which states that there is a difference between groups, can also be speciﬁed. The P value is then calculated, that is, the prob- ability of obtaining a difference as large as or larger than the one observed between the groups, assuming the null hypothesis is true (i. In this situation, we reject the null hypothesis and accept the alternative hypothesis, and therefore conclude that there is a statistically signiﬁcant dif- ference between the groups. In this case, we accept the null hypothesis and conclude that the difference is not attributed to sampling. A P value obtained from a test of signiﬁcance should only be interpreted as a measure of the strength of evidence against the null hypothesis. It is of paramount importance that the correct test is used to generate P values and to estimate a size of effect. Using an incorrect test will inviolate the statistical assumptions of the test and may lead to inaccurate or biased P values. The sample size needs to be large enough so that a deﬁnitive answer to the research question is obtained. However, the sample has to be small enough so that the study is practical to conduct. In general, studies with a small sample size, say with less than 30 participants, can usually only provide imprecise and unreliable estimates. The larger the sample size the more likely a difference between study groups will be statistically signiﬁcant. Therefore, it is important to carefully calculate the sample size required prior to the study commencing and also consider the sample size when interpreting the results of the statistical tests. This handbook should be available for anyone in the team to refer to at any time to facilitate considered data collection and data analysis practices. Suggested contents of data analysis log sheets that could be kept in the study handbook are shown in Box 1. In this, it is important that data are treated carefully and analysed by people who are familiar with their content, their meaning and the interrelationship between variables. Before beginning any statistical analyses, a data analysis plan should be agreed upon in consultation with the study team. The plan can include the research questions or hypotheses that will be tested, the outcome and explanatory variables that will be used, the journal where the results will be published and/or the scientiﬁc meeting where the ﬁndings will be presented. A good way to handle data analyses is to create a log sheet for each proposed paper, abstract or report. The log sheets should be formal documents that are agreed to by all stakeholders and that are formally archived in the study handbook. When a research team is managed efﬁciently, a study handbook is maintained that has up-to-date docu- mentation of all details of the study protocol and the study processes. This is especially important when the data set will be accessed in the future by researchers who are not familiar with all aspects of data collection or the coding and recoding of the variables. Data management and documentation are relatively mundane processes compared to the excitement of statistical analyses but are essential. Laboratory researchers document every detail of their work as a matter of course by maintaining accurate laboratory books. All researchers undertaking clinical and epidemiological studies should be equally dili- gent and document all of the steps taken to reach their conclusions. Documentation can be easily achieved by maintaining a data management book with a log sheet for each data analysis. In this, all steps in the data management processes are recorded together with the information of names and contents of ﬁles, the coding and names of variables and the results of the statistical analyses. Many funding bodies and ethics committees require that all steps in data analyses are documented and that in addition to archiving the data, the data sheets, the output ﬁles and the participant records are kept for 5 years or up to 15 years after the results are published. Although it may be tempt- ing to jump straight into the analyses that will answer the study questions rather than spend time obtaining descriptive statistics, a working knowledge of the descriptive statis- tics often saves time by avoiding analyses having to be repeated for example because outliers, missing values or duplicates have not been addressed or groups with small numbers are not identiﬁed. When entering data, it is important to crosscheck the data ﬁle with the original records to ensure that data has been entered correctly. It is important to have a high standard of 14 Chapter 1 data quality in research databases at all times because good data management practice is a hallmark of scientiﬁc integrity. Describing the charac- teristics of the sample also allows other researchers to judge the generalizability of the results. This is preferable to using an implausible value such as 9 or 999 which was commonly used in the past. If these values are not accurately deﬁned as discrete missing values in Missing column displayed in Variable View, they are easily incorporated into the analyses, thus producing erroneous results. Although these values can be predeﬁned as system missing, this coding scheme is discouraged because it is inefﬁcient, requires data analysts to be familiar with the coding scheme and has the potential for error. In the spreadsheet, the variable for ‘place of birth’ is coded as a string variable. If the variable had been deﬁned as numeric, the missing values would have been omitted. When collecting data in any study, it is essential to have methods in place to pre- vent missing values in, say, at least 95% of the data set. Methods such as restructuring questionnaires in which participants decline to provide sensitive information or train- ing research staff to check that all ﬁelds are complete at the point of data collection are invaluable in this process. In large epidemiological and longitudinal data sets, some missing data may be unavoidable. However, in clinical trials, it may be unethical to col- lect insufﬁcient information about some participants so that they have to be excluded from the ﬁnal analyses.
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