11/20 NTUH & Reading

Mission:
1.Today just finished one paper of BADL and BIB!
2.Read new paper that title is Reliability and validity of the Dynamic Gait Index in persons with chronic stroke!
3.Finding and recheck the number of ICD9 from the old files,but didnt have anyone matched with it.
4.Find out the meaning of the statistical method ,such as Bland and Altman method,concurrent construct validity!

The Bland & Altman plot (Bland & Altman, 1986 and 1999) is a statistical method to compare two measurements techniques. In this graphical method the differences (or alternatively the ratios) between the two techniques are plotted against the averages of the two techniques.

The Bland & Altman plot is useful to reveal a relationship between the differences and the averages (examples 1 & 2), to look for any systematic bias (example 3) and to identify possible outliers. If there is a consistent bias, it can be adjusted for by subtracting the mean difference from the new method.

If the differences within mean ± 1.96 SD are not clinically important, the two methods may be used interchangeably

Repeatability
The Bland and Altman plot may also be used to assess the repeatability of a method by comparing repeated measurements using one single method on a series of subjects. The graph can then also be used to check whether the variability or precision of a method is related to the size of the characteristic being measured.
Since for the repeated measurements the same method is used, the mean difference should be zero. Therefore the Coefficient of Repeatability (CR) can be calculated as 1.96 (or 2) times the standard deviations of the differences between the two measurements (d2 and d1):


This coefficient can be read from the Bland & Altman plot, but can also be calculated using Summary statistics. E.g. if the names of the variables for 2 repeated measurements for FSH concentration are FSH1 and FSH2, then you define a new variable as FSH2-FSH1 and calculate the summary statistics for it. By multiplying the calculated standard deviation by 2 you obtain the coefficient of repeatability.