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Question 1
Incorrect
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Regarding bias, which of the following statements is CORRECT:
Your Answer: Randomisation eliminates bias from a study.
Correct Answer: Bias leads to the systematic difference between the results from a study and the true states of affair.
Explanation:Bias is the term used to describe an error at any stage of the study that was not due to chance. Bias leads to the systematic difference between the results from a study and the true states of affair. Bias may be introduced at all stages of the research process, from study design, through to analysis and publication. Bias can create a spurious association or mask a real association.Good research design can reduce the effect of bias (e.g. blinding, randomisation) but they cannot eliminate it completely. Increasing the sample size does not reduce bias.
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This question is part of the following fields:
- Evidence Based Medicine
- Study Methodology
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Question 2
Incorrect
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All of the following statements are considered true regarding randomized control trials, except:
Your Answer: They can overcome small sample sizes
Correct Answer: They can eliminate the need for further studies
Explanation:Meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research. Outcomes from a meta-analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis. The examination of variability or heterogeneity in study results is also a critical outcome.The benefits of meta-analysis include a consolidated and quantitative review of a large, and often complex, sometimes apparently conflicting, body of literature. The specification of the outcome and hypotheses that are tested is critical to the conduct of meta-analyses, as is a sensitive literature search.Important medical questions are typically studied more than once, often by different research teams in different locations. In many instances, the results of these multiple small studies of an issue are diverse and conflicting, which makes the clinical decision-making difficult. The need to arrive at decisions affecting clinical practise fostered the momentum toward evidence-based medicine. Evidence-based medicine may be defined as the systematic, quantitative, preferentially experimental approach to obtaining and using medical information. Therefore, meta-analysis, a statistical procedure that integrates the results of several independent studies, plays a central role in evidence-based medicine.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 3
Incorrect
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Which of the following data types does a pain-scoring system represent?
Your Answer:
Correct Answer: Ordinal
Explanation:Pain scoring systems are processes for assessing pain and the severity of illnesses that have been scientifically designed and tested. An example of ordinal categorical data is a pain scoring system.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 4
Incorrect
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A study investigating the risk of suffering a stroke in patients with atrial fibrillation taking the new antiplatelet drug ticagrelor, compared with standard treatment with warfarin is done over a 2-year time period. 30 of the 300 patients taking ticagrelor and 20 of the 500 patients taking warfarin suffered a stroke over the 2-year period. One of these statements is true regarding the outcomes of this study.
Your Answer:
Correct Answer: Ticagrelor increases the risk of stroke
Explanation:Absolute risk and relative risk are used to assess the strength of a relationship between a disease and a factor that may affect it.Absolute risk (AR) is the risk of developing a disease over a time period:AR = the number of events that occur in a group / number of people in that groupThe absolute risk reduction (ARR) is the difference between the absolute risk in the control group (ARC) and the absolute risk in the treated group (ART). ARR = ARC – ARTThe control group is the warfarin group, therefore the ARC is 20/500 (0.04). Treatment group is the ticagrelor group and ART = 30/300 (0.1). ARR = 0.04 – 0.1 = -0.06. This shows that treatment with ticagrelor increases risk of developing stroke. This is also termed a relative risk increase.Relative risk, or risk ratio, (RR) is used to compare the risk in the two different groups. It is the ratio of the absolute risks of the disease in the treatment group (ART) to the absolute risk of the disease in the control group (ARC):RR=ART /ARCTherefore RR = 0.1 / 0.04 = 2.5RR < 1 means the intervention reduces the risk of the outcome being studiedRR = 1 means the treatment has no effect on the outcome being studiedRR > 1 means the intervention increased the risk of the outcome being studiedSince RR is 2.5, ticagrelor increases the risk of stroke.SUMMARYAbsolute risk reduction is -0.06Absolute risk in warfarin group = 0.04Relative risk = 2.5Ticagrelor has no effect on stroke is incorrect because RR is not =1
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This question is part of the following fields:
- Evidence Based Medicine
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Question 5
Incorrect
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Which of the following statements accurately describes the number needed to harm?
Your Answer:
Correct Answer: The NNH is the number of patients that need to be treated for one to experience the side effect
Explanation:Number needed to harm (NNH) corresponds to the number of individuals that must be treated, so that one of them presents an adverse reaction accountable to the treatment.Hence, a NNH of 100 means that 100 individuals need to be treated in order to produce an adverse effect of the treatment in one individual.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 6
Incorrect
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Which of these statements about experimental studies is true?
Your Answer:
Correct Answer: Randomisation serves to remove potential bias
Explanation:In experimental studies, the researcher introduces an intervention and studies the effect. The study subjects are allocated into different groups by the investigator through the use of randomisation. Randomisation serves to remove any potential bias.A cohort study is a form of longitudinal, observational study that follows a group of patients (the cohort) over a period of time to monitor the effects of exposure to a proposed aetiological factor upon them.A case-control study is a type observational study. Here, patients who have developed a disease are identified and compared on the basis of proposed causative factors that occurred in the past, to a control group.Clinical trials are experimental studies. Examples include: double blind, single blind, and unblinded studies(both patient and researcher are aware of the treatment they receive)
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This question is part of the following fields:
- Evidence Based Medicine
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Question 7
Incorrect
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What is the interquartile range of the following data set: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70
Your Answer:
Correct Answer: 30
Explanation:5, 10, 15 /20, 25, 30 /35, 40, 45 /50, 60, 70Sample size (n) = 12Median = [(n+1)/2]th value = (12+1)/2 = 6.5 = halfway between 6th and 7th value = (30 +35)/2 = 32.5The lower (first) quartile = halfway between 15 and 20 = 17.5The upper (third) quartile = halfway between 45 and 50 = 47.5The interquartile range is the difference between the upper quartile and lower quartile = 47.5 – 17.5 = 30
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 8
Incorrect
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Identify the type of graph described below: A graph that is a useful summary of a set of bivariate data (two variables), usually drawn before working out a linear correlation coefficient or fitting a regression line.
Your Answer:
Correct Answer: Scatterplot
Explanation:A scatterplot is a useful summary of a set of bivariate data (two variables), usually drawn before working out a linear correlation coefficient or fitting a regression line. It gives a good visual picture of the relationship between the two variables, and aids the interpretation of the correlation coefficient or regression model. Each unit contributes one point to the scatterplot, on which points are plotted but not joined. The resulting pattern indicates the type and strength of the relationship between the two variables.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 9
Incorrect
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All of the following statements are considered true regarding likelihood ratios, except:
Your Answer:
Correct Answer: A likelihood ratio less than 1 indicates that the result is associated with the presence of the disease
Explanation:The Likelihood Ratio (LR) is the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that that same result would be expected in a patient without the target disorder.The LR is used to assess how good a diagnostic test is and to help in selecting an appropriate diagnostic tests or sequence of tests. They have advantages over sensitivity and specificity because they are less likely to change with the prevalence of the disorder, they can be calculated for several levels of the symptom/sign or test, they can be used to combine the results of multiple diagnostic test and they can be used to calculate post-test probability for a target disorder.A LR greater than 1 produces a post-test probability which is higher than the pre-test probability. An LR less than 1 produces a post-test probability which is lower than the pre-test probability. When the pre-test probability lies between 30 and 70 per cent, test results with a very high LR (say, above 10) rule in disease. An LR below 1 produces a post-test probability les than the pre-test probability. A very low LR (say, below 0.1) virtually rules out the chance that the patient has the disease.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 10
Incorrect
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Regarding likelihood ratios, which of the following statements is INCORRECT:
Your Answer:
Correct Answer: Likelihood ratios, like predictive values, are affected by the prevalence of the disease in the population.
Explanation:A likelihood ratio is a measure of the diagnostic value of a test. Likelihood ratios show how many times more likely patients with a disease are to have a particular test result than patients without the disease. Likelihood ratios are more useful than predictive values because they are calculated from sensitivity and specificity and therefore remain constant even when the prevalence of the disorder changes.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 11
Incorrect
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In the Kaplan-Meier plot, which of the following labels should be applied to the X-axis?
Your Answer:
Correct Answer: Time in years
Explanation:Kaplan-Meier estimate is one of the best options to be used to measure the fraction of subjects living for a certain amount of time after treatment. In clinical trials or community trials, the effect of an intervention is assessed by measuring the number of subjects survived or saved after that intervention over a period of time. The time starting from a defined point to the occurrence of a given event, for example death, is called as survival time and the analysis of group data as survival analysis. The graph plotted between estimated survival probabilities/estimated survival percentages (on Y axis) and time past after entry into the study (on X axis) consists of horizontal and vertical lines.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 12
Incorrect
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Which of the following is an example of continuous data:
Your Answer:
Correct Answer: Height
Explanation:Continuous data is data where there is no limitation on the numerical value that the variable can take e.g. weight, height.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 13
Incorrect
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A new blood test is being developed to diagnose DVT. 1000 people presenting to ED with suspected DVT undergo the new blood test and the gold standard doppler ultrasound to confirm the diagnosis. Of the 1000 people, 77 are confirmed to have a DVT. Of the patients diagnosed with DVT, 75 test positive with the new diagnostic test and of the patients not diagnosed with DVT, 125 test positive with the new diagnostic test. What is the negative predictive value of this test:DVT YesDVT NoTotalPositive testa= 75b = 125200Negative testc = 2d = 798800Total779231000
Your Answer:
Correct Answer: 0.99
Explanation:Negative predictive value (NPV) is the proportion of individuals with a negative test result who do not have the disease.Negative predictive value (NPV) = d/(c+d) = 798/800 = 0.99 = 99%This means there is a 99% chance, if the test is negative, that the patient does not have a DVT.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 14
Incorrect
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An analytical cohort study aimed to determine a relationship between intake of dietary calcium and incidence of hip fractures among post-menopausal women. The following are the data obtained from the study:No. of post-menopausal women who took Calcium: 500No. of post-menopausal women who took Calcium and suffered a hip fracture: 10No. of post-menopausal women who took placebo: 500No. of post-menopausal women who took placebo and suffered a hip fracture: 25Compute for the absolute risk in the placebo group.
Your Answer:
Correct Answer: 0.05
Explanation:The absolute risk (AR) is the probability or chance of an event. It is computed as the number of events in treated or control groups, divided by the number of people in that group.AR = 25/500 = 0.05
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This question is part of the following fields:
- Evidence Based Medicine
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Question 15
Incorrect
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What is the interquartile range for these numbers: 11, 4, 6, 8, 3, 10, 8, 10, 4, 12, 31?
Your Answer:
Correct Answer: 7
Explanation:We obtain 3, 4, 4, 6, 8, 8, 10, 11, 12, and 31, and sample size (n) = 11 when we order the data. [(n+1)/2] = median 6th value = (11+1)/2 = [(n+1)/4] represents the bottom (first) quartile. (3rd value = 4th value = (11 + 1)/4 3[(n+1)/4] for the top (third) quartile 3[(11 + 1)/4] = 9th value = 11th value = 11th value = 11th value = 11th value = 11th value = 11th value = 11th value = 11th The difference between the upper and lower quartiles is the interquartile range, which is equal to 11 minus 4 = 7.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 16
Incorrect
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Regarding box and whisker plots, which of the following statements is true?
Your Answer:
Correct Answer: 25% of the values lie below the lower quartile
Explanation:A box and whisker plot is defined as a graphical method of displaying variation in a set of data. In most cases, a histogram analysis provides a sufficient display, but a box and whisker plot can provide additional detail while allowing multiple sets of data to be displayed in the same graph.The procedure to develop a box and whisker plot comes from the five statistics below:(1) Minimum value: The smallest value in the data set(2) Second quartile: The value below which the lower 25% of the data are contained(3) Median value: The middle number in a range of numbers(4) Third quartile: The value above which the upper 25% of the data are contained(5) Maximum value: The largest value in the data set
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This question is part of the following fields:
- Evidence Based Medicine
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Question 17
Incorrect
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A range of one standard deviation above and below the mean includes what approximate percentage of the sample values:
Your Answer:
Correct Answer: 0.68
Explanation:A range of one SD above and below the mean (+/- 1 SD) includes 68.2% of the sample values.A range of two SD above and below the mean (+/- 2 SD) includes 95.4% of the sample values.A range of three SD above and below the mean (+/- 3 SD) includes 99.7% of the sample values.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 18
Incorrect
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Regarding forest plots, which of the following is the purpose of this graph?
Your Answer:
Correct Answer: To graphically display the relative strength of multiple studies attempting to answer the same question
Explanation:The results of meta-analysis are often displayed graphically in a forest plot. A properly constructed forest plot is the most effective way to graphically display the relative strength of multiple studies attempting to answer the same question. A typical meta-analysis consists of three main objectives that include estimation of effect sizes from individual studies and a pooled summary estimate with their confidence intervals (CIs), heterogeneity among the studies, and any publication bias. The forest plot illustrates the first two of these objectives. Forest plots visualize the effect measure and CI of individual studies, which provide the raw data for the meta-analysis, as well the pooled-effect measure and CI. The individual studies also can be grouped in the forest plot by some of their characteristics for ease of interpretation such as by study size or year of publication. When comparing the outcomes between an intervention and a control group, dichotomous outcome variables are expressed as ratios (i.e. odds ratios, ORs or risk ratios, RRs), while for continuous outcomes, a weighted mean difference is reported.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 19
Incorrect
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Which of the following is considered an example of an observational study?
Your Answer:
Correct Answer: Cohort study
Explanation:The two most common types of observational studies are cohort studies and case-control studies; a third type is cross-sectional studies.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 20
Incorrect
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All of the following statements are considered true regarding L'Abbe plots, except:
Your Answer:
Correct Answer: Treatment group results are plotted on the horizontal axis
Explanation:A L’Abbé plot is a scatter plot with the risk in the control group on the x-axis and the risk in the experimental group on the y-axis. It can be used to evaluate heterogeneity in meta-analysis. Furthermore, this plot can aid to choose a summary measure (odds ratio, risk ratio, risk difference) that will result in more consistent results.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 21
Incorrect
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Regarding a cohort study, which of the following statements is INCORRECT:
Your Answer:
Correct Answer: It is useful for rare diseases.
Explanation:A cohort study is a longitudinal, prospective, observational study that follows a defined group (cohort) matched to unexposed controls for a set period of time and investigates the effect of exposure to a risk factor on a particular future outcome. The usual outcome measure is the relative risk (risk ratio). A large sample size is required for a rare outcome of interest so it is not useful for rare diseases.
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This question is part of the following fields:
- Evidence Based Medicine
- Study Methodology
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Question 22
Incorrect
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A 58-year-old man presented to the emergency room complaining of a chest pain that has been going on for the past 12 hours. Upon further investigation, a troponin test was ordered and the results came back negative. He was given a discharge order from the emergency department.Which of the following aspects of this test is considered the most significant in the decision made that it was safe to send the patient home?
Your Answer:
Correct Answer: Likelihood ratio
Explanation:The Likelihood Ratio (LR) is the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that that same result would be expected in a patient without the target disorder.The LR is used to assess how good a diagnostic test is and to help in selecting an appropriate diagnostic tests or sequence of tests. They have advantages over sensitivity and specificity because they are less likely to change with the prevalence of the disorder, they can be calculated for several levels of the symptom/sign or test, they can be used to combine the results of multiple diagnostic test and they can be used to calculate post-test probability for a target disorder.A LR greater than 1 produces a post-test probability which is higher than the pre-test probability. An LR less than 1 produces a post-test probability which is lower than the pre-test probability. When the pre-test probability lies between 30 and 70 per cent, test results with a very high LR (say, above 10) rule in disease. An LR below 1 produces a post-test probability les than the pre-test probability. A very low LR (say, below 0.1) virtually rules out the chance that the patient has the disease.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 23
Incorrect
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Which statement about cross-sectional studies is true?
Your Answer:
Correct Answer: They can be used to assess the prevalence of a condition
Explanation:Cross-sectional studies can be used to assess the prevalence of a condition.Cross-sectional studies CANNOT be used to differentiate between cause and effect or establish the sequence of events.They can be used to study multiple outcomes but are NOT suitable for studying rare diseases.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 24
Incorrect
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An analytical cohort study is done to compare the relationship between omega 3 intake and occurrence of myocardial infarction (MI) among males aged over 65 years. The following are the data from the study:No. of subjects taking placebo: 100 menNo. of subjects taking placebo who suffered an MI: 15 menNo. of subjects taking omega 3: 100 menNo. of subjects taking omega 3 who suffered an MI: 5 menCompute for the absolute risk in the treatment (omega 3) group.
Your Answer:
Correct Answer: 0.05
Explanation:The absolute risk (AR) is the probability or chance of an event. It is computed as the number of events in treated or control groups, divided by the number of people in that group.AR = 5/100 = 0.05
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This question is part of the following fields:
- Evidence Based Medicine
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Question 25
Incorrect
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The interquartile range (IQ) is often displayed using which of the following:
Your Answer:
Correct Answer: Box and whisker plot
Explanation:A boxplot is a vertical or horizontal rectangle used to display the interquartile range, with the ends of the rectangle corresponding to the upper and lower quartiles of the data values. The box contains 50% of the data values. A line drawn through the rectangle corresponds to the median value. Whiskers, starting at the ends of the rectangle usually indicate the minimum and maximum values, therefore the entire box and whisker plot represents the range. Any outliers can be plotted independent of the box and whisker plot.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 26
Incorrect
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Which of the following risk ratios indicates no difference in risk between two groups:
Your Answer:
Correct Answer: 1
Explanation:A risk ratio of 1 indicates no difference in risk between groups.If the risk ratio of an event is > 1, the rate of that event is increased in the exposed group compared to the control group.If the risk ratio is < 1, the rate of that event is reduced in the exposed group compared to the control group.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 27
Incorrect
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One of these statements about cohort studies is true:
Your Answer:
Correct Answer: They are longitudinal in nature
Explanation:A cohort study is a longitudinal, observational study. It follows a group of patients (the cohort) forward in time and monitors the effects of the aetiological factor under study upon them.Cohort studies are usually of longer duration and are more expensive than case-control studies. They, however, provide more useful and reliable information.Cohort studies follow a cohort of patients who don’t have a disease and evaluate the absolute and relative risk of contracting the disease after exposure to the aetiological agent.Cross-sectional studies are the best way to determine the prevalence of a disease. while Cohort studies are better at determining the incidence of a disease.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 28
Incorrect
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A new test is being developed to diagnose chlamydia. 1000 people aged 15 – 35 years attending a GUM clinic undergo the new test and the current gold standard nucleic acid amplification test (NAAT) to confirm the diagnosis. Of the 1000 people, 250 are diagnosed with chlamydia. Of the patients diagnosed with chlamydia, 240 test positive with the new diagnostic test and of the patients not diagnosed with chlamydia, 150 test positive with the new diagnostic test. What is the negative predictive value of this test:Chlamydia YesChlamydia NoTotalPositive testa= 240b = 150390Negative testc = 10d = 600610Total2507501000
Your Answer:
Correct Answer: 0.98
Explanation:Negative predictive value (NPV) is the proportion of individuals with a negative test result who do not have the disease.Negative predictive value (NPV) = d/(c+d) = 600/610 = 0.98 = 98%This means there is a 98% chance, if the test is negative, that the patient does not have chlamydia.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 29
Incorrect
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The following statements about cross-sectional studies are true EXCEPT?
Your Answer:
Correct Answer: They can be used to determine the relative risk of a condition
Explanation:The UK national census is an example of a cross-sectional study.Cross-sectional studies can be used to assess the prevalence of a condition, and support or refute inferences of cause and effect.Cross-sectional studies are observations of the frequency and characteristics of a disease in a given population at one particular point in time. Cross-sectional studies do not differentiate between cause and effect and also do not establish the sequence of events.Cross-sectional studies cannot be used to calculate the relative risk of a condition.
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This question is part of the following fields:
- Evidence Based Medicine
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Question 30
Incorrect
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A p value < 0.05 obtained from a study with a significance level (α) of 0.05, means all of the following, EXCEPT:
Your Answer:
Correct Answer: the result is clinically significant.
Explanation:A p value < 0.05:is statistically significantmeans that the probability of obtaining a given result by chance is less than 1 in 20means the null hypothesis is rejectedmeans there is evidence of an association between a variable and an outcomeNote that this does not tell us whether the result is clinically significant.
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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SESSION STATS - PERFORMANCE PER SPECIALTY
