Christian Sonesson

A review and discussion of prospective statistical surveillance in public health

A review of methods suggested in the literature for sequential detection of changes in public health surveillance data is presented. Many researchers have noted the need for prospective methods. In recent years there has been an increased interest in both the statistical and the epidemiological literature concerning this type of problem. However, most of the vast literature in public health monitoring deals with retrospective methods, especially spatial methods. Evaluations with respect to the statistical properties of interest for prospective surveillance are rare. The special aspects of prospective statistical surveillance and different ways of evaluating such methods are described. Attention is given to methods that include only the time domain as well as methods for detection where observations have a spatial structure. In the case of surveillance of a change in a Poisson process the likelihood ratio method and the Shiryaev-Roberts method are derived. Copyright 2003 Royal Statistical Society.

Optimal Surveillance Based on Exponentially Weighted Moving Averages

Abstract Statistical surveillance is used to detect an important change in a process as soon as possible after it has occurred. The exponentially weighted moving averages (EWMA) method is used in industry, economics, and medicine. Three optimality criteria of surveillance are studied. The average run length (ARL) criterion violates commonly accepted inference principles, and the drawbacks are demonstrated. The expected delay criterion is based on the minimal expected delay from change to detection. The full likelihood ratio method is optimal according to this criterion. Approximations of this method turn out to be modifications of the EWMA method. The approximations lead to a formula for the optimal value of the smoothing parameter of the EWMA statistic. The usefulness of this formula is shown. It is demonstrated that, for EWMA, the minimax criterion agrees well with that of the ED criterion but not with that of the ARL criterion.

Evaluations of some Exponentially Weighted Moving Average methods

The need for statistical surveillance has been noted in many different areas, and examples of applications include the detection of an increased incidence of a disease, the detection of an increased radiation level and the detection of a turning point in a leading index for a business cycle. In all cases, preventive actions are possible if the alarm is made early. Several versions of the EWMA (Exponentially Weighted Moving Average) method for monitoring a process with the aim of detecting a shift in the mean are studied both for the one-sided and the two-sided case. The effects of using barriers for the one-sided alarm statistic are also studied. One important issue is the effect of different types of alarm limits. Different measures of evaluation, suitable in different types of applications, are considered such as the expected delay, the ARL¹, the probability of successful detection and the predictive value of an alarm, to give a broad picture of the features of the methods. Results from a large-scale simulation study are presented both for a fixed ARL0 and a fixed probability of a false alarm. It appears that important differences from an inferential point of view exist between the one- and two-sided versions of the methods. It is demonstrated that the method, usually considered as a convenient approximation, is to be preferred over the exact version in the overwhelming majority of applications.

Expression of delta opioid receptor mRNA and protein in the rat cerebral cortex and cerebellum is decreased by growth hormone

Hormones released from the pituitary have been shown to regulate the expression of different proteins in the central nervous system. We wanted to examine whether peripheral administration of bovine growth hormone (bGH) regulates the expression of delta‐opioid receptor (DOR) in the cerebral cortex and cerebellum. Expression of the DOR protein was quantified using Western blot densitometry. DOR mRNA was quantified with a solution hybridization RNase protection assay. Hypophysectomized (Hx) and untreated normal female rats were included in the study. All Hx rats were hormonally treated with cortisol (400 μg/kg/day) and L‐thyroxine (10 μg/kg/day) for 19 days. Hypophysectomy resulted in a threefold increase in cerebral cortex and a twofold increase in cerebellum of the DOR protein compared with normal rats. One subgroup of Hx rats received bGH (1 mg/kg body weight) as a daily subcutaneous injection for 19 days. This treatment normalized the levels of DOR protein in the cerebral cortex and cerebellum. Immunohistochemical experiments showed that GH decreased DOR expression especially in layers II–VI in cerebral cortex and in stratum moleculare in cerebellum. Quantification of DOR mRNA by solution hybridization RNase protection assay corresponded to the DOR protein measurements. We conclude that the expression of DORs in cerebral cortex and cerebellum is regulated by GH.

Symphysis–fundus measurements for detection of small for gestational age pregnancies

Background. In Sweden measurements of the symphysis–fundus (SF) distance are used to detect small for gestational age (SGA) pregnancies. The aim of this study was to evaluate the efficiency of Swedish ultrasound‐based SF reference curves in detecting SGA pregnancies.

Relative growth estimated from self-administered symphysis fundal measurements

Objective . To establish absolute‐ and relative‐growth reference curves for the detection of intrauterine growth restriction from weekly self‐administered symphysis‐fundus (SF) measurements and to assess the influence of fetal sex, maternal obesity and parity. Design. Prospective longitudinal study. Setting. Pregnant women from six primary antenatal care centres. Population. Three hundred women with singleton ultrasound dated pregnancies. Methods. Weekly self‐administered SF measurements from gestational week 25 until delivery were obtained. A linear mixed longitudinal model was used to estimate the absolute SF growth using the natural logarithm (lnSF). Relative lnSF growth was calculated as the lnSF measurement in one gestational week subtracted by the lnSF measurement in the previous gestational week. The influence of fetal sex, maternal obesity and parity was assessed in regression models and by a graphical display. Main Outcome Measures. Absolute lnSF and relative lnSF growth curves and influence of fetal sex, maternal obesity and parity on these. Results. SF measurements from 191 women were used to establish an SF‐growth reference. The absolute lnSF growth was influenced by maternal obesity, and for fetal sex and parity, borderline significance was recorded; while there was no evidence that the relative lnSF growth could depend on these variables. Conclusions. Weekly self‐administered SF measurements can be obtained and used to estimate SF growth. Relative growth of the lnSF height seems to be independent of fetal sex, maternal obesity and parity.

Self‐administered measurement of symphysis‐fundus heights

Background. Antenatal identification of infants small for gestational age (SGA) improves their perinatal outcome. Repeated measurement of symphysis‐fundus (SF) heights performed by midwives is the most widespread screening method for detection of SGA. However, the inefficiency of this method necessitates improved practices. Earlier start and more frequent SF measurements, which could be accomplished by self‐administered measurements, might improve the ability to detect deviant growth. The present study was set up to evaluate whether pregnant women can reliably perform SF measurements by themselves. Method. Forty healthy women with singleton and ultrasound‐dated pregnancies from 2 antenatal clinics in Uppsala, Sweden, were asked to perform 4 consecutive SF measurements once every week, from 20 to 25 weeks of gestation until delivery. The self‐administered SF measurements were recorded and systematically compared with midwives’ SF measurements. Results. Thirty‐three pregnant women performed self‐administered SF measurements over a 14‐week period (range: 1–21). The SF curves constructed from self‐administered SF measurements had the same shape as previously constructed population‐based reference curves. The variance for self‐administered SF measurements was higher than that of the midwives. Conclusions. Pregnant women are capable of measuring SF heights by themselves, but with higher individual variance than midwives. Repeated measurements at each occasion can compensate for the higher variance. The main advantage of self‐administered SF measurements is the opportunity to follow fetal growth earlier and more frequently.

Self-administered symphysis–fundus measurements analyzed with a novel statistical method for detection of intrauterine growth restriction: a clinical evaluation

Objective. To assess the ability of self‐administered symphysis–fundus measurements used with the Shiryaev–Roberts statistical method (SR method) to identify growth‐restricted (IUGR) fetuses and compare it with the traditional SF method (symphysis–fundus measurements used with a population‐based reference curve). Design. Longitudinal study. Setting. Pregnant women attending primary antenatal care centres. Population. From a population of 1 888 women with singleton ultrasound‐dated pregnancies, we analyzed data from 1 122 women. Methods. Weekly self‐administered SF measurements from gestational week 25 until delivery were analyzed according to the SR method. Neonatal morbidity and small for gestational age (SGA) were used as proxies for IUGR. Small for gestational age was defined as a birthweight less than two standard deviations (SD) and <10th percentile. We assessed the sensitivity of the SR and the SF methods to detect neonatal morbidity and SGA. Main Outcome Measures. Birth‐related mortality, respiratory distress, hypoglycemia, Apgar score ≤6 at five minutes, pH ≤7.00 in the umbilical artery, neonatal care, preterm delivery, operative delivery for fetal distress and SGA. Results. For the SR method, the sensitivity for neonatal morbidity was between 6.0 and 36.4%, for SGA <2SD 36.8%, and for SGA <10th percentile 20.9%. The SF method had a sensitivity between 6.0 and 13.8% for neonatal morbidity, 52.3% for SGA <2SD and 28.6% for SGA <10th percentile. Conclusions. The SR and the SF methods had low sensitivities for neonatal morbidity.