How many times are the odds of being dyspeptic on sertraline higher than the odds of being dyspeptic on placebo?
B. This question looks at the odds ratio. It is an estimate of how many times more likely it was that a person who experienced a problem (dyspepsia) was exposed to the supposed cause (risk factor) than was a control subject (those not exposed to the risk factor). Let us consider the data in the table in a different way: the number of people who developed dyspepsia is 8 and those who did not develop dyspepsia is 75. The ‘odds’ of an event happening is the ratio of the probability of its occurrence to the probability of its non-occurrence. So in patients with dyspepsia, the probability of being on sertraline is A/A + C = 6/8 = 0.75. The probability of being on a placebo is C/A + C = 2/8 = 0.25. Therefore the odds of a person with nausea being on sertraline is 0.75/0.25 = 3 or simply A/C. Similarly, we can also calculate the odds of the person ‘without dyspepsia’ being on sertraline. It is 38/37 (B/D) = 1.02, i.e. the odds of having used sertraline in those who did not have nausea is 1.02. The ratio of these odds is simply called the odds ratio. The ratio = (A/C)/(B/D) or (AD/BC). That is, 3/1.02 or 6 × 37/2 × 38 = 222/76 = 2.92. The odds ratio is interpreted in a manner more or less similar to the relative risk. Confidence intervals are provided and interpreted in the same manner. Odds ratios are usually used in case control studies and in meta-analysis as primary summary measures.
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The finding of a hypothetical cost-effectiveness analysis of a new model of psychotherapy in depression is shown in the table below (questions 87-91):
Calculate the average cost-effectiveness ratio (ACER) for the new treatment?
A. As cost-effectiveness analysis has been applied to healthcare, researchers have used predominantly two methods of calculating the summary measure – the average ACER and incremental cost-effectiveness ratio (ICER). The ACER captures the average cost per effect, i.e. cost of treatment/effect of treatment. In this case, the cost of the new psychotherapy is £10,000 and the effect is 50 depression-free weeks. In the above question, the ACER for the new treatment (psychotherapy) will be C/E = 10,000/50 = £200. The ACER for antidepressants from the question will be 5000/45 = £111.
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Calculate the incremental cost-effectiveness ratio (ICER) for the new treatment:
A. In contrast to ACER, the ICER reports the ratio of the change in cost to the change in effect (for example ΔC/ΔE). In plain and simple language, this pretty much translates to the extra cost per extra effect, i.e. ΔC/ΔE. From the question, we can see ΔC = 10,000 – 5000 = 5000; ΔE = 50 – 45 = 5 weeks. So, ΔC/ΔE = 5000/5 = £1000. Again in plain language, this would mean that compared with antidepressants, the new treatment would cost an average of 1000 additional pounds per one added depression-free week. In many economic evaluations, the ICER indicates that a new treatment is relatively more costly (ΔC >0) and relatively more effective (ΔE >0) than usual care, as in the situation in the question. Now, it is for the decision makers to decide if this additional money is worth spending.
What is the incremental net benefit (INB) if the health commissioners are willing to pay around £1500 per additional depression free week?
C. An INB calculation determines whether the net benefit of a new treatment outdoes that of usual care. In our case, the net benefit of psychotherapy surpasses the benefit of using antidepressants. In general, the INB is calculated by valuing ΔE in pounds and then subtracting the associated ΔC. This is where the society’s willingness to pay for the additional depression week comes into play. INB is calculated using the formula (ΔE × λ) – ΔC, where λ is society’s willingness to pay for a 1-unit gain of effect. In our question, ΔE = 5 weeks; the service managers are willing to pay around £1500/each depression free week (λ – willingness to pay) and ΔC is £5000. So, INB = (5 × 1500) – 5000 = 7500 – 5000 = £2500. The INB equation computes the net value of patient outcome gained in pounds. When the INB is positive, the value of a new treatment’s extra benefits (ΔE × λ) outweighs its extra costs (ΔC). In short, society values the extra effect more than the extra cost (i.e. ΔE × λ >ΔC). Conversely, when the INB is less than 0, society (or your health service management) does not consider the extra benefit worth the extra cost.
After critically appraising the above cost-effectiveness analysis paper, managers of an NHS foundation trust decide to choose psychotherapy over antidepressants as the first-line management for depression.
Which of the following statements best defines the opportunity costs?
C. Resources are scarce and are relative to needs. The use of resources in one way prevents their use in other ways. For example, if a city council decides to build a hospital on a piece of huge vacant land in the middle of the city, the city forgoes the opportunity to benefit from the next best alternative such as selling the land to decrease the current debt or building a shopping mall that would generate additional income for the council. Opportunity cost is assessed in not just monetary or material terms, but in terms of anything which is of value. The opportunity cost of investing in a healthcare intervention is best measured by the health benefits that could have been achieved had the money been spent on the next best alternative intervention. In this example the cost of not providing the ‘next best alternative’, antidepressant therapy, is the opportunity cost of providing psychotherapy as the first choice treatment.
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