Noise and the trading mechanism:the case of SETS

On 20 October 1997 the London Stock Exchange introduced a new trading system called SETS. This system was to replace the dealer system SEAQ, which had been in operation since 1986. Using the iterative sum of squares test introduced by Inclan and Tiao (1994), we investigate whether there was a change in the unconditional variance of opening and closing returns, at the time SETS was introduced. We show that for the FTSE-100 stocks traded on SETS, on the days following its introduction, there was a widespread increase in the volatility of both opening and closing returns. However, no synchronous volatility changes were found to be associated with the FTSE-100 index or FTSE-250 stocks. We conclude therefore that the introduction of the SETS trading mechanism caused an increase in noise at the time the system was introduced.

Ambulatory electroencephalogram in children:a prospective clinical audit of 100 cases

Ambulatory electroencephalogram has been used for differentiating epileptic from nonepileptic events, recording seizure frequency and classification of seizure type. We studied 100 consecutive children prospectively aged 11 days to 16 years that were referred for an ambulatory electroencephalogram to a regional children's hospital. Ambulatory electroencephalogram was clinically useful in contributing to a clinical diagnosis in 71% of children who were referred with a range of clinical questions. A diagnosis of epileptic disorder was confirmed by obtaining an ictal record in 26% and this included 11 children that had previously normal awake and or sleep electroencephalogram. We recommend making a telephone check of the current target event frequency and prioritising those with typical events on most days in order to improve the frequency of recording a typical attack.