By: David Robertson MD
Avoid ‘‘loaded’’ words and stereotypes that suggest that there is a most desirable answer purchase 40 mg propranolol with amex coronary artery job. Sometimes it is useful to set a tone that permits the respondent to admit to behaviors and attitudes that may be considered undesirable. For example, when asking about a patient’s compliance with prescribed medications, an interviewer or a questionnaire may use an introduction: ‘‘People sometimes forget to take medications their doctor prescribes. It is important to give respondents permission to admit certain behaviors without encouraging them to exaggerate. Collecting information about potentially sensitive areas like sexual behavior or income is especially difﬁcult. Some people feel more comfortable answering these types of questions in self-administered questionnaires than in interviews, but a skillful interviewer can sometimes reveal open and honest answers. In personal interviews, it may be useful to put potentially embarrassing responses on a card so that the respondent can answer by simply pointing to a response. Setting the Time Frame Many questions are designed to measure the frequency of certain habitual or recurrent behaviors, like drinking alcohol or taking medications. To measure the frequency of the behavior it is essential to have the respondent describe it in terms of some unit of time. If the behavior is usually the same day after day, such as taking one tablet of a diuretic every morning, the question can be very simple: ‘‘How many tablets do you take a day? To measure these, the investigator must ﬁrst decide what aspect of the behavior is most important to the study: the average or the extremes. For example, a study of the effect of chronic alcohol intake on the risk of cardiovascular disease may need a measurement of average consumption during a period of time. On the other hand, a study of the role of alcohol in the occurrence of falls may need to know how frequently the respondent drank enough alcohol to become intoxicated. Questions about average behavior can be asked in two ways: asking about ‘‘usual’’ or ‘‘typical’’ behavior or counting actual behaviors during a period of time. For example, an investigator may determine average intake of beer by asking respondents to estimate their usual intake: About how many beers do you have during a typical week (one beer is equal to one 12-oz can or bottle, or one large glass)? It assumes, however, that respondents can accurately average their behavior into a single estimate. Because drinking patterns often change markedly over even brief intervals, the respondent may have a difﬁcult time deciding what is a typical week. Faced with questions that ask about usual or typical behavior, people often report the things they do most commonly and Chapter 15 Designing Questionnaires and Interviews 247 ignore the extremes. Asking about drinking on typical days, for example, will underestimate alcohol consumption if the respondent drinks unusually large amounts on weekends. During the last 7 days, how many beers did you have (one beer is equal to one 12-oz can or bottle, or one large glass)?
A study without randomization results in the violation of the probability distribution assumption and consequently no accurate and reliable statistical inference on the evaluation of the safety and eﬃcacy of the study drugcan be drawn discount propranolol 40mg line arteries medical term. Mixingup treatment codes can distort the statistical analysis based on the population or randomization model. Consider a two-group parallel design for comparing a test drug and a control (placebo), where n1 patients are randomly assigned to the treatment group and n2 patients are randomly assigned to the control group. When randomization is properly applied, the population model holds and responses from patients are normally distributed. Consider ﬁrst the simplest case where two patient populations (treatment and control) have the same variance σ2 and σ2 is known. Let µ and µ be the population means 1 2 for the treatment and the control, respectively. Intuitively, mixingup treatment codes does not affect the signiﬁcance level of the test. A straightforward calculation shows that x¯1−x¯2 is still normally distributed with variance σ2 1 + 1, but the mean of x¯ − x¯ is equal n1 n2 1 2 to 1 1 1 − m + (µ1 − µ2). Considerations Prior to Sample Size Calculation It turns out that the power for the test deﬁned above is p(θm)=Φ(θm − zα/2)+Φ(−θm − zα/2), where 1 1 µ1 − µ2 θm = 1 − m +. For example, suppose that when there is no mix-up, p(θ) = 80%, which gives that |θ| =2. Hence, a small proportion of mixed-up treatment codes may seriously affect the probability of detectingtreatment effect when such an effect exists. In this simple case we may plan ahead to ensure a desired power when the maximum proportion of mixed-up treatment codes is known. Assume that the maximum proportion of mixed-up treatment codes is p and that the original sample size is n1 = n2 = n0. The effect of mixed-up treatment codes is higher when the study design becomes more complicated. The test statistic is necessarily modiﬁed by replacing z α/2 and σ2 by t and α/2;n1+n2−2 (n − 1)s2 +(n − 1)s2 2 1 1 2 2 σˆ =, n1 + n2 − 2 where s2 is the sample variance based on responses from patients in the 1 treatment group, s2 is the sample variance based on responses from patients 2 in the control group, and tα/2;n1+n2−2 is the upper (α/2)th percentile of the t-distribution with n1+n2−2 degrees of freedom. When there are m patients with mixed-up treatment codes and µ1 = µ2, the effect on the distribution of x¯1 − x¯2 is the same as that in thecaseofknownσ2. A direct calculation shows that the expectation of σˆ2 is 2 2 2 2(µ1 − µ2) m 1 1 E(ˆσ)=σ + 2 − m +. In practice, however, we may end up with an imbalance in sample sizes across centers. It is a concern (i) what the impact is of this imbalance on the power of the test and (ii) whether sample size calculation should be performed in a way to account for this imbalance. In this section, we examine this issue by studyingthe power with sample size imbalance across centers. Under the above model, a test statistic for µ1 − µ2 =(µ + T1) − (µ + T2)=T1 − T2 is given by J ∗ 1 T = (¯y1j − y¯2j) J j=1 with E(T∗)=T − T and 1 2 2 J ∗ σ 1 1 Var(T)= 2 (+).
These may take the form of practice guidelines generic 80 mg propranolol mastercard arteries reversed around heart, clinical pathways, or evidence-based textbook summaries of a clinical area) Increasingly, easy electronic access to all these levels of evidence-based resources have become available, along with strategies and tools to interpret and integrate evidence from published research in patient care. However, this approach to providing clinicians with research has meant winnowing out virtually all medical research except the abbreviated compiled results of randomized or controlled clinical trials. Department of Education has taken action to support a movement for evidencebased practice in education. S C I E N T I F I C R E S E A R C H A N D E V I D E N C E B A S E D P R A C T I C E 19 offers an opportunity to bring rapid, evidence-driven progress to U. To address the opportunity, the Coalition for EvidenceBased Policy undertook a collaborative initiative with the Education Department to explore how the Department can most effectively use its new authority to advance. Fund studies that randomly assign students to treatment and control groups, in order to establish what works in educating children, and 2. Provide strong incentive for the widespread use of educational practices proven effective in such randomized controlled trials. The rationale is that this strategy would be key to reversing decades of stagnation in education and sparking rapid, evidence-driven progress. The report urges the Department to make a concerted effort to support randomized controlled trials, support a knowledge base of these proven interventions, and spur their wide-spread use in order to fundamentally improve the effectiveness of American education. Recommendation to create the infrastructure within the Department for this proposed strategy: >> the Department should identify High Priority Areas in which there is a critical need to (i) build the knowledge base of proven interventions or (ii) provide incentives for their widespread use. Recommendation to build the knowledge base of effective, replicable interventions in High Priority Areas: >> the Department should focus its discretionary funds for research and evaluation on randomized trials to identify such interventions. S C I E N T I F I C R E S E A R C H A N D E V I D E N C E B A S E D P R A C T I C E 20 >> the Department’s grant program should give applicants major incentive to use their discretionary funds to carry out such randomized trials. This would enable the Department to leverage a much larger pool of resources to carry out this strategy. Such incentives would include: (i) additional funding for the applicant from the funding sources listed above, (ii) in discretionary grant programs, signiﬁcant additional points in the proposal evaluation process; (iii) waiving of certain statutory and/or regulatory requirements (a strategy used effectively by the Department of Health and Human Services to get states to test welfare programs in randomized trials); and (iv) positive recognition and publicity. Recommendation to provide strong incentives for the widespread use of proven interventions: >> the Department’s grant program should require applicants to provide a plan for widespread implementation of research-proven interventions, with quantiﬁable goals. This would apply to both formula and discretionary grant programs (discretionary programs would make this plan an important factor in the proposal evaluation process). Importantly, each applicant would be responsible for choosing which interventions, backed by randomized trials, to include in its plan. In High Priority Areas, the Department would require an independent evaluation, after grant award, of whether the applicant meets the goals of its plan. The Department would annually issue a high-proﬁle report summarizing the results of these evaluations, including the progress of each state agency and other major grantee in implementing research-proven interventions. The Coalition’s report concludes that the above recommendations can all be implemented within the Department of Education’s existing statutory authority.
Nonparametric methods for comparing variabilities between treatment groups cheap 40 mg propranolol with mastercard cardiovascular disease conference 2015, however, are much more complicated and require further research. The primary hypothesis is that there are no treatment differences across the treatment groups. Let xij be the observation from the ith subject receivingthe jth treatment, where i = 1. Similar to the analysis of variance model for the parametric case, we consider the followingmodel: xij = µ + τj + eij =1. Nonparametrics where µ is the unknown overall mean, τj is the unknown jth treatment k effect and j=1 τj =0. Itisassumedthat(i)eachei comes from the same continuous population with mean 0 and (ii) the ei’s are mutually independent. The hypotheses of interest are H0 : τ1 = ···= τk versus Ha : τi = τj for some i = j. To test the above hypotheses, the followingKruskal-Wallis test is useful k (Kruskal and Wallis, 1952). Let Rij denote the rank of xij in this joint nj N+1 ranking, Rj = i=1 Rij, R·j = Rj/nj,andR·· = 2, j =1. Note that Rj is the sum of the ranks received by treatment j and R·j is the average rank obtained by treatment j. Based on Rj, R·j and R··,the Kruskal-Wallis test statistic for the above hypotheses can be obtained as k 12 2 H = nj(R·j − R··) N(N +1) j=1 k 2 12 Rj = − 3(N +1). N(N +1) nj j=1 We reject the null hypothesis at the α level of signiﬁcance if H ≥ h(α, k, n1, ···,nk), where h(α, k, n1, ···,nk)satisﬁes P(H ≥ h(α, k, n1, ···,nk)) = α under the null hypothesis. Values of h(α, k, (n1, ···,nk)) are given in the most standard nonparametric references. Note that under the null hypothesis, H has an asymptotic chi-square distribution with k−1 degrees of freedom (Hollander and Wolfe, 1973). Thus, we may reject the null hypothesis at the α level of signiﬁcance for large samples if H ≥ χ2,whereχ2 is the upper αth percentile of a chi-square α,k−1 α,k−1 distribution with k − 1 degrees of freedom. Unlike the parametric approach, formulae or procedures for sample size calculation for testingdifference in multiple-sample locations using nonparametric methods are much more complicated. Practical Issues 371 much larger than that of the standard therapy (or control), safety of the test product could be a concern. In practice, a replicate crossover design or a parallel-group design with replicates is usually recommended for comparing intra-subject variability. Although nonparametric methods for testing scale parameters are available in the literature (see.
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