2 Phases of a Full Clinical Trial Phase I – the trial takes place after the development of a therapy and is designed to determine doses, strengths and safety – it is pre-experimental – there is no control groupPhase II – the trial is looking for evidence of effectiveness – it is pre-experimental or quasi-experimental and similar to a pilot test – it seeks to determine feasibility of further testing and signs of potential side effects
3 Phases of a Full Clinical Trial Phase III – it is a full experimental test of the therapy with randomly assigned treatment and control groups. It is designed to determine whether the intervention is more effective than a standard treatment. It may be referred to as and RCT or randomized clinical trial and often studies large groups from multiple sites.
4 Phases of a Full Clinical Trial Phase IV – it occurs after the decision to adopt an innovative therapy and involves study of its long-term consequences –both side effects and benefits. It rarely requires true experimental design.
5 Prevalence StudiesPrevalence studies are a type of descriptive study that come from the field of epidemiology. They are conducted to determine the prevalence rate of some condition. They are cross-sectional designs that obtain data from one population at risk for the condition
6 Prevalence Studies The formula for a prevalence rate (PR) is: Example: # of cases with the condition at a given point in time_____________________________________ x K# in the population at risk for being a caseExample:80 cases____________ x 100 (# we want the PR established for) = 16 per 100500 at risk
7 Incidence StudiesIncidence studies measure the frequency of developing new cases. This requires a longitudinal design, because we need to determine who is at risk for becoming a new case.
8 Incidence Studies The formula for an incidence rate (IR) is: Example: # of new cases with the condition over a given period of time_____________________________________ x K# in the population at risk for being a new caseExample:21 new cases (in one year since original count)____________ x = 5 per 100420 at risk (from previous example: =420 now at risk
9 Relative RiskRelative risk (RR is the risk of becoming a case in one group compared to another.Example:If the risk of becoming a new case was 7 per hundred in men and 14 per hundred in women, we would divide the rate of women by the rate of men, and find that women were twice as likely to become a new case over a year’s time.
10 Relative RiskRelative Risk can also be used in examining new therapies.Relative Risk is the ratio of an outcome (such as PONV) in the treatment group (those receiving a bolus of fluid before induction) to the rate of the outcome (PONV) in the controls.An RR of < 1.0 means the experimental group had less (PONV) than the control group. An RR of > 1.0 would mean that the experimental group had more (PONV) than did the controls.
11 Relative RiskRelative Risk can also be used in examining other differences in groups.Example:The risk of LBW with and without smokingWithout smoking: 144/2309 = .06 had LBWWith smoking: / = .10 had LBWRR is: / = 1.67
12 Describing RiskAbsolute risk is the proportion of people who experienced an undesirable outcome in each groupAbsolute risk reduction (ARR) is the number used to describe the estimated proportion of people who would be spared from an adverse outcome through exposure to an interventionRelative risk reduction (RRR) is the estimated proportion of untreated risk that is reduced through exposure to the intervention
13 Odds RatioRatio of the odds for the treated versus the untreated group, with the odds reflecting the proportion of people with the adverse outcome relative to those without it.The OR is at least equal to the RR, but often overestimates it.
14 Odds RatioWhen OR = 1.00, it means the odds that something will happen to one group are equal to the odds that it will happen to another group.If one group smoked and the other did not, we might obtain an OR of 3.00, meaning that the odds of those who smoked would be 3 x higher than those who did not.
15 Number Needed to Treat (NNT) Estimate of how many people would need to receive the intervention to prevent one adverse outcome
16 Developing Screening/Diagnostic Instruments Goal is to establish a cutoff point that balances sensitivity and specificity
17 Positive Predictive Value The Positive Predictive Value (PPV) - the precision rate, or the post-test probability of disease - is the proportion of patients with positive test results who are correctly diagnosed. It indicates the probability with which a positive test might show the disease or condition being tested for. It is a measure of the diagnostic test. A low number means a high “false positive” rate.PPV = No. of true positivesNo. of true positives + No. of false positives(total who test positive)
18 Negative Predictive Value The Negative Predictive Value (NPV) is the proportion of patients with negative test results who are correctly diagnosed.NPV = No. of true negativesNo. of true negatives + No. of false negatives(total who test negative)
19 Criteria for Assessing Screening/Diagnostic Instruments Sensitivity: the instrument’s ability to correctly identify a “case”—i.e., to diagnose a conditionSpecificity: the instrument’s ability to correctly identify noncases, that is, to screen out those without the condition
20 EMPIRICALEVIDENCE ofCONDITIONTrueFalseTestOutcomePositiveTrue positiveFalse Positive(Type I error)Positive Predictive ValueNegativeFalse negative(Type II error)True negativeNegative Predictive ValueSensitivitySpecificity
22 Information from Slide 19 Looking at the slides you can see that the large number of false positives and the low number of false negatives indicate that the occult blood test is poor at confirming colon cancer. However, it is good as a screening test since 99.5 % of the negative tests will be correct and the sensitivity indicates that further testing needs to be done on at least 66.7% of those testing positive.
23 Confidence IntervalThe Confidence Interval (CI) is the range of values around a sample mean that are calculated to contain the population mean with a 95% (or 99%) degree of certainty. Many researchers believe that these values give more clinical data than do p values.
24 Confidence IntervalThe POINT ESTIMATE is a single point estimated to be the mean for the population, based on a sample. When a confidence interval (CI) is reported, it is an INTERVAL ESTIMATE, a range of values that estimate the mean for a population. If a math test was given to a sample of nursing students and there was a mean of 55, then 55 would be the point estimate. If the 95% CI was reported as 52-57, there would be a 95% chance that the true mean of all nursing students would be between
25 Confidence Interval SD (of the sample) The STANDARD ERROR OF THE MEAN is used to calculate the CI. The standard error of the mean is the error that is due to sampling. Each sample mean is likely to deviate somewhat from the true population mean. The SEM is the difference between the sample mean and the unknown population mean. It is the margin of error to allow for when estimating the population mean from a random sample. It allows for chance errors. It is calculated as follows: SD (of the sample)Square root of the No. of people in the sample
26 Confidence IntervalIf the SEM is 3 and the mean is 100 and you want a confidence interval of 95% - that is between and SD from the mean, you would use the following formula: X + (1.96 x SEM) = CI( x 3) =We can say, with 95% confidence, that the population mean would fall between and
27 Confidence IntervalFor a 68% CI, add the standard error of the mean (SEM) to the mean, then subtract it from the mean. For a 95% CI , multiply the SEM by 1.96, then add and subtract. For a 99% CI, multiply by 2.58, then add and subtract. Note: The intervals obtained by using these multipliers are only precise with large numbers (60 or more cases).