help cisd2

Title

cisd2 -- Estimation of measurement variation from dual interchangeable measurements.

Syntax

cisd2 varname [, level(#)]

Description

With dual interchangeable measurements, the loneway command
estimates the measurement error, to be displayed as
Estimated SD within id. However, the uncertainty of this
estimate is not displayed. cisd2 takes the difference between
two variables as input and calculates the confidence interval for
the estimated SD.

varname is the name of a variable containing the difference
between the dual measurements. It is input as the sole variable in
a regress command with the noconstant option.

cisd2 displays the SD(error) estimate with confidence interval
for the difference variable and for the individual measurements,
by dividing by sqrt(2).

The 95% confidence limits for an SD estimate are functions of SD
and DF (degrees of freedom):
Lower limit: SD*sqrt(DF/invchi2(DF,0.975))
Upper limit: SD*sqrt(DF/invchi2(DF,0.025))

Examples

. generate dif = sbp1-sbp2
. cisd2 dif
. cisd2 dif , level(90)

Authors

Morten Frydenberg and Svend Juul
School of Public Health, Aarhus University, Danmark
Email: morten@biostat.au.dk