Repeatability versus ICC versus Concord

[Larissa G. Baraldi]

Dear all,

I would like to hear about you if there is any alternative to do Repeatability analisys instead ICC or Concord (Lin) , which , by the way, some times is difficult to choose between them.

In our validation study we apply the same questionnarie to the same person by the same interviewer. As I understood this is a repeatability analisys, but i'm having difficult to select the best command to evaluet this. Can someone help me ?

best wishes,

Larissa

[Marcos Almeida]

Hello Larissa,

I just wish to underline that Concord is a SSC, written by Nick Cox and Thomas Steichen.

That said, I guess this user-written program shall not be what you wish. In general, it provides the rho_c between two continous variables. Also, it performs great Bland and Altman's plots.

Unfortunately, you didn't give much information on your questionnaire (type of variable, number of questions, etc), neither your data.

I believe you will get more insightful advice provided you share this sort of information, as recommended in the FAQ.

Best,

Marcos

[Nick Cox]

Thanks to Marcos for the mention, to which I will add a few details below, but most crucially for this thread I don't think that concordance correlation sounds at all pertinent. But to say more we'd need more information on the questionnaire data.

The first author in a series of publications on the concordance correlation coefficient was always Thomas [Tom] J. Steichen and the thread to follow starts in the Stata Technical Bulletin and continues in the Stata Journal.

I have to point out that the version on SSC is not the latest. See SJ 10-4.

SJ-10-4 st0015_6 . . . . . . . . . . . . . . . . Software update for concord
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
Q4/10 SJ 10(4):691
update explicitly supporting plot() and addplot() and
allowing systematic control of the reference line

SJ-8-4 st0015_5 . . . . . . . . . . . . . . . . Software update for concord
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
Q4/08 SJ 8(4):594
dialog box modified to correct visual layout problems

SJ-7-3 st0015_4 . . . . . . . . . . . . . . . . Software update for concord
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
Q3/07 SJ 7(3):444
now compatible with Stata 10; help file updated

SJ-6-2 st0015_3 . . . . . . . . . . . . . . . . Software update for concord
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
Q2/06 SJ 6(2):284
updated for compatibility with Stata 9 by() option

SJ-5-3 st0015_2 . . . . . . . . . . . . . . . . Software update for concord
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
Q3/05 SJ 5(3):470
minor bug fix for concord

SJ-4-4 st0015_1 . . . . . . . . . . . . . . . . Software update for concord
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
Q4/04 SJ 4(4):491
rewritten to provide dialog, Stata 8 graphs, and two
new tests

SJ-2-2 st0015 . . . . . . A note on the concordance correlation coefficient
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
Q2/02 SJ 2(2):183--189
correction based on an erratum for Lin's concordance
correlation coefficient, and assessment of the impact of
the change

STB-58 sg84.3 . . . . Concordance correlation coefficient: minor corrections
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
11/00 p.9; STB Reprints Vol 10, p.137
small bug fixes affecting user control through the connect(),
symbol(), and pen() options

STB-54 sg84.2 . . . Concordance correlation coefficient: update for Stata 6
(help concord if installed) . . . . . . . T. J. Steichen and N. J. Cox
3/00 pp.25--26; STB Reprints Vol 9, pp.169--170
updated to version 6 with corrections and new option for
saving the standard normal plot

STB-45 sg84.1 . . . . . . . . Concordance correlation coefficient, revisited
(help concord if installed) . . . . . . . . T. Steichen and N. J. Cox
9/98 pp.21--23; STB Reprints Vol 8, pp.143--145
improvements to the concord command

STB-43 sg84 . . . . . . . . . . . . . . Concordance correlation coefficient
(help concord if installed) . . . . . . . . T. Steichen and N. J. Cox
5/98 pp.35--39; STB Reprints Vol 8, pp.137--143
computes Lin's (1989) concordance correlation coefficient for
agreement on a continuous measure obtained by two persons or
methods

We collaborated through initial contact on Statalist and met just once at a users' meeting somewhere in the US. Tom has now retired [twice!] and has given me carte blanche to take over the project. Somewhere on my to-do list is to try to bring all these bits together in an expository piece.

[Larissa G. Baraldi]

Dear Marcos and Nicx, thaks for your reply.

So, to be more precise in my question: I intend to validate a questionnaire about individual skills. In that we have 10 questions, each one has four options of answer on a likert scale. I have applied this questionnaire in 58 persons and after about 10 days i've applied it again. I was thinking that concordance analysis could give me a good idea of repeatability as it gives me the product of precision and accuracy. unfortunatelly i got great results the accuracy, but poor results of precision .... I do not know if this is the best choice but when i think about the other option (ICC comand) it seems to me that it is more inaccurate ....