Which one of the following study designs would be best suited to assess the incidence of secondary pelvic malignancy in patients receiving external beam radiotherapy for prostate cancer?
Sampling in a case-control study is determined by a disease state, not an exposure status. The controls represent the population at risk of the disease (but do not have it) and the cases that have the disease. Case-control studies can either be unmatched (the controls are selected at random from the population at risk) or matched where each case is matched with a control for potential confounding variables. In case-control studies, a form of observational study, subjects are observed and therefore not randomised. Cohort studies contrast with case-control studies in that the subjects are sampled based on their exposure, or not, to a variable of interest and then observed until the outcome being investigated occurs. Cohort studies are therefore an example of a longitudinal study design because subjects are followed over time. Data acquisition can either be prospective or retrospective. Intervention studies, which are another form of longitudinal study, do allow for randomisation of subjects to intervention or treatment groups. Randomised controlled trials (RCTs) are a true experimental study design and provide optimal evidence in healthcare on the effectiveness of treatments/healthcare interventions specific to a population of interest. RCTs should, wherever possible, incorporate some element of ‘blinding’ of subjects (patients), healthcare providers and/or data collectors to provide the most robust evidence. RCTs should be reported according to the CONSORT statement. A cross-sectional study is a descriptive study and makes estimates of features of the population of interest at a single time point or over a continuous short period of time. It is commonly used to determine prevalence of disease in a population.
In a Kaplan–Meier curve, which term describes removing subjects from the survival analysis who have not completed follow-up at the designated time point?
A Kaplan–Meier curve is a commonly used analysis to calculate survival after a treatment using lifetime data. Censoring correctly describes the process of removing subjects from a survival analysis if they have not completed follow-up at the stipulated time-point and can be incorporated in a Kaplan–Meier analysis. Intention-to-treat analysis describes an analysis methodology that, instead of removing subjects that deviate from an agreed protocol, includes them all in the final analysis based on their initial treatment intent. Listwise deletion describes removal of a record if a single data item is missing. It is a generic method for handling missing data in statistics and is not particular to Kaplan–Meier analysis. Rounding up or rounding down a figure is commonly used in mathematics to simplify interpretation.
In a non-randomised controlled study evaluating the hypothesis that laparoscopic nephrectomy, as compared with open nephrectomy, reduces the length of hospital stay; the null hypothesis was inappropriately accepted. This is known as?
A type I error (or false positive error) is said to have occurred when a null hypothesis, which is true, is inappropriately rejected. The probability of making a type I error is equal to the chosen significance level (p-value). Conversely, when a null hypothesis, which is false, fails to be rejected, a type II error (or false negative error) is said to have occurred. The probability of not making a type II error equals the power of the test. Publication bias is not related to hypothesis testing and statistical error.
A controlled study, which sequentially allocates consecutive patients to either monopolar TURP or HoLEP to compare short-term outcomes between the two treatment modalities, provides which level of evidence?
The use of levels of evidence, in evidence-based medicine, is a means by which the reader can stratify, in a standardised manner, the evidence according to its quality. A number of systems have been designed for this purpose, including that produced by the Oxford Centre for Evidence-Based Medicine ; a modified version of which is used by the European Association of Urology clinical guidelines to formulate its grades of recommendations.
In a study evaluating medical therapy for lower urinary tract symptoms, men are randomly allocated to 5-alpha-reductase inhibitor (n = 100) or placebo (n = 100) and subsequently monitored for progression to an episode of acute urinary retention (AUR). In the placebo arm 25 men developed AUR compared with 20 in the 5ARI arm. What is the probability of progressing to AUR in those taking the 5ARI?
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