Báo cáo y học: "Statistics review 2: Samples and populations" potx

... individ- ual values generally lie close to the mean, and this is reflected in the tall, narrow distribution. Review Statistics review 2: Samples and populations Elise Whitley* and Jonathan Ball † *Lecturer ... distribution is extremely non-Normal and the sample size is very small then it may be necessary to use non- parametric methods. (These will be discussed in a subse- quen...

Ngày tải lên: 12/08/2014, 18:21

Ngày tải lên: 12/08/2014, 19:22

... between 7.0 and 7.9 g/dl, and so on). These categories can be defined in any way and need not necessarily be of the same width, although it is generally more convenient to have equally sized groups. ... are a useful way of describing both qualitative and grouped quantitative data and there are also many types of graph that provide a convenient summary. Qualitative data are commonly...

Ngày tải lên: 12/08/2014, 18:21

... sufficiently small P value. Similarly, a study with high statistical power will, by definition, make iden- tification of any difference relatively easy, but this can only be achieved in a sufficiently ... improved oxygenation but that this was not reflected in any significant reduction in survival at 10 days (the primary end-point). Mortality rates at 10 days were 21% and 25% in the prone...

Ngày tải lên: 12/08/2014, 18:21

... Statistics review 1) may be used before performing any calculations. Similarly, transformations may also be useful if the SDs are very differ- ent in the unpaired case [3]. However, it may not always ... usual way. The only difference is in the calculation of the SE. Table 3 Mean and standard deviation of mean arterial pressure Mean arterial pressure (mmHg) Standard Early goal-directed t...

Ngày tải lên: 12/08/2014, 19:21

... than some hypothesized value, and considers whether this is substantially different from what we would expect by chance. If any observations are exactly equal to the hypothesized value they are ignored ... be Normally distributed, whereas the sign test only requires that they are independent of one another. Alternatively, the dis- crepancy may be a result of the difference in power provided...

Ngày tải lên: 12/08/2014, 19:21

Ngày tải lên: 12/08/2014, 19:22

... according to genotype and disease outcome ARDS Genotype Yes No Total CC or CT 11 208 219 TT 1 182 183 Total 12 390 402 Presented are data on outcomes from a study conducted by Quasney and coworkers ... in the study into early goal-directed therapy in the treatment of severe sepsis and septic shock by Rivers and coworkers [5], one of the outcomes measured was in- hospital mortality. Of...

Ngày tải lên: 12/08/2014, 20:20

... age > 65 years or ≤ 65 years, and (b) long-term oxygen therapy (LTOT) before intensive care unit admission (yes/no). The P values are for the log rank test. 391 test the null hypothesis that ... measuring survival time, the start and end-points must be clearly defined and the censored observations noted. Only the most commonly used techniques are introduced in this review. Kaplan–Me...

Ngày tải lên: 12/08/2014, 20:20

... ed. New York, USA: John Wiley and Sons; 2000. 3. Bewick V, Cheek L, Ball J: Statistics review 7: Correlation and regression. Crit Care 2003, 7:451-459. 4. Bewick V, Cheek L, Ball J: Statistics review ... model, though this may not always be the case because of correlations between the explanatory variables. Several models may produce equally good statistical fits for a set of data an...

Ngày tải lên: 12/08/2014, 20:21