Báo cáo y học: "Statistics review 4: Sample size calculations" doc

... study. Put simply, this is the probabil- ity of correctly identifying a difference between the two groups in the study sample when one genuinely exists in the populations from which the samples ... larger sample size in order to obtain a sufficiently small P value. Similarly, a study with high statistical power will, by definition, make iden- tification of any difference relatively easy...

Ngày tải lên: 12/08/2014, 18:21

... away the sample mean is from this hypothesized value, the less likely it is that the difference arose by chance. The t statistic, from which a P value is derived, is as follows. sample mean – hypothesized ... subsequent treatment may increase central venous oxygen saturation beyond the level expected by chance. However, the P value in isolation gives no information about the likely size...

Ngày tải lên: 12/08/2014, 19:21

... 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. However, the categories must ... plots Unordered Ordered Discrete Continuous Ventilatory support Severity of illness Days in ICU Blood pressure Main types: In tables, shown as: Graphically shown as: Types: Examples: Table 1 Haemo...

Ngày tải lên: 12/08/2014, 18:21

... distribution of sample means is approximately Normal and that the popula- tion SD can be approximated by the sample SD. These assumptions, particularly the first, will generally be valid if the sample ... 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- quent review....

Ngày tải lên: 12/08/2014, 18:21

... 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 b...

Ngày tải lên: 12/08/2014, 19:21

Ngày tải lên: 12/08/2014, 19:22

Ngày tải lên: 12/08/2014, 19:22

... viable in this type of study, but RR is generally easier to interpret. The AR indicates that 14.4% of the successful outcomes can be directly attributed to the early goal-directed therapy and is calculated ... prospective cohort study conducted by Quasney and coworkers [1] of 402 adults admitted to the Memphis Methodist Healthcare System with community-acquired pneumonia. That study investiga...

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 ... bronchiectasis Explanatory 95% confidence variables Risk ratio interval P Age (>65 years) 2.7 1.15–6.29 0.022 LTOT (yes) 3.12 1.47–6.90 0.003 LTOT, long-term oxygen therapy. ... time, the star...

Ngày tải lên: 12/08/2014, 20:20

... binary (e.g. death or survival), then the probability distribution of the number of deaths in a sample of a particular size, for given values of the explanatory Review Statistics review 14: Logistic ... http://ccforum.com/content/9/1/112 variables, is usually assumed to be binomial. The probability that the number of deaths in a sample of size n is exactly equal to a value r is gi...

Ngày tải lên: 12/08/2014, 20:21