Time series analysis of births of children with orofacial clefts.

Observation of the dates when children with orofacial clefts were born, gives the impression that they were born in clusters, between which there were intervals of different duration. An analysis was therefore undertaken of the period between 1972 to 1997 when 1112 such children were born. For diagnostic checking of stationarity of the time series the Box-Ljung test was used. Since it was found that the time series was stationary, analysis of autocorrelation function was performed. The results confirmed the impression that children with clefts are born in clusters, between which there are gaps of different duration. This suggests that the birth of a child with a cleft is not a random and independent event.