Methodologic issues regarding the use of three observational study designs to assess influenza vaccine effectiveness
Evan OrensteinGaston De SerresMichael HaberDavid K. ShayCarolyn B. BridgesPaul GargiulloWalter A. Orenstein
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Background Influenza causes substantial morbidity and annual vaccination is the most important prevention strategy. Accurately measuring vaccine effectiveness (VE) is difficult. The clinical syndrome most closely associated with influenza virus infection, influenza-like illness (ILI), is not specific. In addition, laboratory confirmation is infrequently done, and available rapid diagnostic tests are imperfect. The objective of this study was to estimate the joint impact of rapid diagnostic test sensitivity and specificity on VE for three types of study designs: a cohort study, a traditional case-control study, and a case-control study that used as controls individuals with ILI who tested negative for influenza virus infection. Methods We developed a mathematical model with five input parameters: true VE, attack rates (ARs) of influenza-ILI and non-influenza-ILI and the sensitivity and specificity of the diagnostic test. Results With imperfect specificity, estimates from all three designs tended to underestimate true VE, but were similar except if fairly extreme inputs were used. Only if test specificity was 95% or more or if influenza attack rates doubled that of background illness did the case-control method slightly overestimate VE. The case-control method usually produced the highest and most accurate estimates, followed by the test-negative design. The bias toward underestimating true VE introduced by low test specificity increased as the AR of influenza- relative to non-influenza-ILI decreases and, to a lesser degree, with lower test sensitivity. Conclusions Demonstration of a high influenza VE using tests with imperfect sensitivity and specificity should provide reassurance that the program has been effective in reducing influenza illnesses, assuming adequate control of confounding factors.To determing the efficacy of a single influenza vaccine administration in the elderly receiving annual influenza vaccination, antibody response to influenza vaccine was compared between once and twice injections in a geriatric cohort. Influenza vaccination had been done for 69 inpatients in the year prior to the study, and was administered twice for 34 of them and once for the other 35 during the study period. Influenza vaccine was injected twice to 77 inpatients who had not received influenza vaccine in the year prior to the study.Hemoagglutination inhibition (HI) antibody titer for influenza A/H1N1, A/H3N2, and B was measured before vaccination, after the first vaccination, after the second vaccination, and after the epidemic period, September 1995 to April 1996. HI antibody titer prior to vaccination was significantly higher in the patients who had received influenza vaccination the previous year. The influenza vaccine induced an increase in HI titer in almost all subjects, and the geometric mean of the HI titer after vaccination in the patients who received vaccine once was comparable to that of the patients injected vaccine twice. The number of patients with HI titers of over 128×increased, and the frequency ranged from 60.0% to 97.1% for the influenza viruses of the three subtypes. The frequency of HI titers over 128×was not significantly different among the three groups. The second vaccination did not increase the number of patients with HI titers over 128×when compared with the number after the first injection in the patients who had received influenza vaccine the previous year. These results suggest that prior vaccination does not diminish the antibody response to influenza vaccine in the elderly. The efficacy of a single influenza vaccination is comparable to that achieved by twice injections in the elderly receiving annual influenza vaccination.
Antibody response
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72 preschoolers and 72 school children observed the original discrimination of nonreversal shift (NRS) followed by 14 NRS trials by themselves. The observational trials were 10 or 30 in each age group. The correct (_??_) or incorrect (×) responses on the 1st (unchanged pair) and the 2nd (changed pair) trials of NRS were mainly measured. In preschoolers, both dependent observational-learning mode (_??_-× responses: DOL) and independent observational-learning mode (_??_-_??_ and ×-×: IOL) were found, but no observational-trial effects on the modes were found. In school children, DOL occurred significantly more than IOL in both groups, and the observational-trial effect was also found. Subproblem analyses suggested that the _??_-× responses were indeed the “dependent” mode rather than the “independent” one.
Observational learning
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Observational methods such as OW AS. RULA. and REBA have been widely used to identify posture-related risks of musculoskeletal disorders in industry, since they are useful and efficient in evaluating postural stresses. However. there are few studies comparing the methods and providing guidelines for selecting and using the methods. They have been developed based on different backgrounds and with different application areas. Each method has its own characteristics. which must be considered in selecting and using them. In this study. 17 male subjects evaluated 42 different working postures that frequently assumed in the automobile assembly line using a psychophysical method. The postures were then evaluated by different observational methods. The results of the observational methods were compared with psychophysically evaluated stresses. The observational methods resulted in different values of stresses for certain postures. For some postures showing high values of perceived discomfort. the observational methods showed different values of stresses. These results showed that the observational methods should be used differently according to application area and they have some weak points to be improved.
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The purposes of this study were to develop and implement an observational training program and to assess the effects of a video observational training program on video and live observational proficiency. Physical education majors took a pretest in both a video and a live environment to assess observational proficiency. The task was observing children batting and answering questions regarding the critical features of the movement. The students were then placed into either a treatment ( n = 12) or a control ( n = 11) group. There were no differences between groups on either assessment ( p > .05). The treatment group then participated in a video observational training program. After the training, all subjects took a posttest in each environment to assess observational proficiency. The training was found to be effective in improving video observational proficiency ( p < .05) but not live observational proficiency ( p > .05). These results provide support for the effectiveness of video observational training in developing video observational proficiency but not live observational proficiency.
Observational learning
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Studies can be observational or experimental. With an observational study, the investigator does not determine the assignment of subjects, and there might not be a control group. If there is a control group, assignment of the independent variable (exposure or intervention) is not under the control of the investigator. Observational studies can be rigorously conducted, but the lack of random assignment of the exposure/intervention introduces confounding and bias. Thus, the quality of evidence resulting from observational studies is lower than that of experimental randomized controlled trials (RCTs). An observational study might be performed if an RCT is unethical, impractical, or outside the control of the investigator. There are many types of prospective and retrospective observational study designs. However, an observational study design should be avoided if an experimental study is possible. Sophisticated statistical approaches can be used, but this does not elevate an observational study to the level of an RCT. Regardless of quality, an observational study cannot establish causality.
Causality
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The article describes the basic rules for conducting observational studies, in particular, registers. The principles of the assessment of its quality and impact on the results are discussed. The potential for evaluating therapeutic effect and side effects in randomized controlled trials (RCTs) and observational studies is compared. Effects of one drug identified in RCTs and observational studies are compared.
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