Modeling and correction of digit preference in tuberculin surveys.
METHODS
Human observers generally have a strong tendency to round analog measurements or estimates to 'nice' ending digits, such as 0, 5, or even numbers. This is known as digit preference; it is a well-known phenomenon in frequency distributions of indurations collected in tuberculin surveys. Digit preference can distort estimates of prevalence and other statistical parameters.


METHODS
We have developed a statistical model that combines smoothing by penalized likelihood and the transfer of counts from non-preferred to preferred digits, to obtain estimates of: 1) the smooth underlying distribution and 2) the amount of digit preference.


RESULTS
To illustrate the validity of the model, it was applied to data from several countries.


CONCLUSIONS
With the proposed model, digit preference can be quantified and frequency distributions of indurations can be corrected for it.
Eilers
P H C
PH
Department of Medical Statistics, Leiden University Medical Centre, Leiden, The Netherlands. p.eilers@lumc.nl
Borgdorff
M W
MW
D000465:Algorithms; D015982:Bias; D002755:Choice Behavior; D003627:Data Interpretation, Statistical; D006801:Humans; D016013:Likelihood Functions; D015233:Models, Statistical; D015203:Reproducibility of Results; D014374:Tuberculin Test / Q000706:statistics & numerical data*