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Types of Research Studies
Experimental studies: Randomized control trial (RCT) can determine efficacy of treatmentrandom Non-random study Observational studies: Cohort study risk factors/ outcomeslongitudinalincidence Cross-sectional study prevalencesnapshotassoc. between risk factors & diseaseused to generate hypothesis (Ho) & sometimes to test Ho Case-control study cases (disease positive) compared to controls (disease negative)looks at odds of exposure Case report series one person or small group of people detailed info used to generate Ho Reviews: Meta-analysis data from multiple studies combined and analyzed Systematic reviews Experts: Expert opinions & panels Grades of evidence in research studies Meta-analysis and systemic reviews are the research studies with the best evidence, grade 1 evidence. Randomized control trials follow closely, then…
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Bias in Research Studies
Bias refers to a systematic error in a research or statistical study. The first large category of bias we will look at is selection bias. Selection bias occurs when those selected for a study are not properly selected or when they are not all retained in a cohort study. The following are subtypes of this bias. Sampling bias also called ascertainment bias occurs when the study population is different from the target population because during selection of subjects there was no randomization. Remember, we can not put the entire population into a study, so the sample we select should be as representative as possible. To do this, we can use…
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Biostatistics Formulas
Part 1: The formulas Part 2: Explanation of the formulas Formulas & Tables Disease + Disease – Test + true positive (TP)a False negative (FN)b a+b PPV = a/(a+b) Test – False positive (FP)c True negative (TN)d c+d NPV = d/(c+d) a+c b+d total SN = a/(a+c) SP = d/(b+d) For Diagnostic tests Formula Sensitivity, SN (true-positive rate) = TP/ (TP +FN) which is a/(a+c) Specificity, SP (true-negative rate) = TN/ (TN + FP) which is d/(b+d) Positive predictive value (PPV) = TP / (TP + FP), which is a/(a+b) Negative predictive value (NPV) = TN / (TN + FN), which is d/(c+d) Incidence rate = # of new cases…
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Receiver Operating Characteristics (ROC) curve
What is an ROC curve? ROC curves are made to help decide on a good cutoff point for a test. If the cutoff is very high, there will be too many false negatives but few false positives. Whereas, if the cutoff is too low there will be too many false positives and few false negatives. To do this, the true positive rate (sensitivity) and false positive rate (1 – specificity) of the test are calculated for several possible cutoff points. Then these are plotted to create the ROC curve and the area under the curve can be measured to determine the overall accuracy of a test. Notice that the ROC…
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Biostatistics Questions
A new blood test to detect prostate cancer is evaluated in 300 male volunteers. A needle biopsy of the prostate gland is done on all men with serum prostate-specific antigen concentrations greater than 5 ng/mL (N<4). One hundred men undergo biopsy procedures; 90 are found to have prostate cancer, and five are found to have chronic prostatitis. Which of the following is necessary to calculate the sensitivity of this test? (A) Incidence of chronic prostatitis in the general population (B) Number of men with test results greater than 5 ng/mL and a normal biopsy specimen (C) Prevalence of chronic prostatitis in the general population (D) Prostate biopsies of men with…