Approximate percentiles for ratios of f-variates

The need for percentiles of ratios of independent F-variates arises in many types of applications. Some tabulated values are available mostly for equal or nearly equal degrees-of-freedom cases, but it is not possible to provide comprehensive tables for the numerous combinations of possible degrees-of-freedom and probability levels. A simple approximation for the percentiles based on the Cornish-Fisher expansion technique is provided which is adequate for larger degrees-of-freedom and a more complicated approximation is provided which is suitable for all cases. The accuracy of the approximation is shown over a wide range of typical cases     

Distinguishing Mother–Infant Interaction From Stranger–Infant Interaction at 2, 4, and 6 Months of Age

Observers watched videotaped face‐to‐face mother–infant and stranger–infant interactions of 12 infants at 2, 4, or 6 months of age. Half of the observers saw each mother paired with her own infant and another infant of the same age (mother tapes) and half saw each infant paired with his or her mother and with a stranger (infant tapes). Observers were asked to judge which was the mother–infant dyad in each pair. Observers' accuracy improved as infants aged and was above chance for both mother and infant tapes when infants were 6 months. Differences between mother–infant and stranger–infant dyadic communication patterns also emerged as the infants aged. At 6 months, mother–infant dyads had more symmetrical communication and less asymmetrical communication than stranger–infant dyads.