Appraising directness

Systematic reviews are usually conducted to summarize several articles on therapy, but they may also be used to answer questions on diagnosis, prognosis or harm. We begin to analyse a systematic review by appraising how directly it addresses the question raised, i.e. how well the PEO in the study corresponds to our own PEO. The issue of directness of studies on therapy, diagnosis, harm and prognosis has been discussed in detail in Chapters 2-5. When we look at systematic reviews on this topic,...

Individualizing the results

When satisfied that biologic and socioeconomic differences do not compromise the applicability of a test in your setting, the next step is to determine the impact that the test (and its results) might have on your specific patient's probability of having a disease. While studies of diagnosis report the average effect of a test on probability of disease, the effect may vary greatly from patient to patient. The main source of this variation is the individual's baseline probability of disease,...

References

1 Pfeffer MA, Swedberg K, Granger CB, Held P, McMurray JJ, Michelson EL, Olofsson B, Ostergren J, Yusuf J, Pocock S and CHARM Investigators and Committees. 2003. Effects of candesartan on mortality and morbidity in patients with chronic heart failure the CHARM-Overall programme. Lancet. 362 759-766. 2 Hannan EL, Wu C, Bennett EV, Carlson RE, Culliford AT, Gold JP, Higgins RSD, Isom OW, Smith CR, and Jones RH. 2006. Risk stratification of in-hospital mortality for coronary artery bypass graft...

Assessing applicability Biologic issues affecting applicability

As in previous chapters, applicability of findings of studies on prognosis can be affected by biologic factors that include sex, co-morbid conditions, race, age and pathology. Tackle Box 5.1 Reporting prognosis in pictures Instructions The results of prognosis studies are often reported in survival curves. Usually, the x-axis represents time and the y-axis is scaled from 100 survival (top) to 0 survival (at the bottom). Go through this tackle box to learn more about interpreting survival...

Question 1 How large was the effect of treatment

The magnitude of the treatment effect may be expressed by comparing outcomes in the treatment and control groups. As described earlier, outcomes can be reported either as 1. continuous variables, which have a range of possible results (e.g. change in weight, or change in quality of life on a scale of zero to one) or 2. dichotomous variables, which have only one of two possible results (e.g. dead or alive, hospitalized or not). When the outcomes are continuous, the effect of treatment is simply...