Dennis B. Gillings

A benefit of spinal manipulation as adjunctive therapy for acute low-back pain: a stratified controlled trial.

Fifty-four subjects volunteered to participate in a controlled study contrasting spinal manipulation with spinal mobilization without the rotational forces and leverage required to move facet joints. All suffered from regional low-back pain for less than 1 month, were ages 18–40, had never previously undergone any form of spinal manipulation, and denied a prior episode of backache within the previous 6 months. Randomization was stratified at outset into those who suffered for less than 2 weeks and those whose discomfort had persisted for 2–4 weeks. Outcome was monitored by a questionnaire assessing functional impairment. A treatment effect of manipulation was demonstrated only in the strata with more prolonged illness at entry. In the first week following manipulation, these patients improved to a greater degree (P=.009, t test) and more rapidly (P <.025, Wilcoxon rank-sum test).

A review of some statistical methods for covariance analysis of categorical data.

Three general methods for covariance analysis of categorical data are reviewed and applied to an example from a clinical trial in rheumatoid arthritis. The three methods considered are randomization-model nonparametric procedures, maximum likelihood logistic regression, and weighted least squares analysis of correlated marginal functions. A fourth heuristic approach, the unweighted linear model analysis, is an approximate procedure but it is easy to implement. The assumptions and statistical issues for each method are discussed so as to emphasize philosophical differences between their rationales. Attention is given to computational differences, but it is shown that the methods lead to similar results for analogous problems. It is argued that the essential differences between the methods lie in their underlying assumptions and the generality of the conclusions which may be drawn.

Retinopathy of prematurity. Diagnosis, severity, and natural history.

This article presents data gathered in a prospective clinical trial of constant monitoring of oxygen therapy on the diagnosis, severity (as coded by a severity index [SI]) and natural history of retinopathy of prematurity (ROP) in 214 surviving infants with birthweights less than or equal to 1300 g. ROP developed in 119 (55.6%) infants and, of these, cicatricial ROP developed in nine (7.6%). The disease was diagnosed at 8-9 weeks on the average in infants with birthweights less than 900 g and 4-5 weeks in infants 900 to 1300 g. Those infants in whom the disease regressed, ROP lasted approximately 15 weeks. The severity of the disease, as defined by the SI, was strongly correlated with the birthweight of the infant and weakly correlated with the total duration of oxygen therapy.

Some Views on Parametric and Non-Parametric Analysis for Repeated Measurements and Selected Bibliography

A common feature of many statistical investigations is the collection of data from groups of experimental units each of which is observed under two or more conditions. Such studies are generally called either split-plot experiments or repeated measurements experiments. This paper is concerned with reviewing general statistical strategies for the analysis of data from these types of research designs. For this purpose, primary attention is directed at two basic dimensions. One of these is the nature of the randomization processes for the data as obtained among and within the experimental units. The other is the level of the measurement scale as either nominal, ordinal, or interval. This framework is then used as the basis of discussion of alternative statistical methods such as repeated measurements analysis of variance, multivariate analysis of variance, and their non-parametric rank and categorical data counterparts in both a general sense and for some specific classes of examples. Finally, a selected bibliography of references for these and related methods is given.

Retinopathy of Prematurity: A Randomized, Prospective Trial of Transcutaneous Oxygen Monitoring

To determine whether the use of continuous transcutaneous oxygen monitoring (tcPO2) could reduce the incidence of retinopathy of prematurity (ROP) in pre-term infants receiving oxygen therapy, a randomized, prospective trial of constant monitoring using the transcutaneous oxygen monitor versus intermittent monitoring of oxygen was performed on a population of premature infants at very high risk for the development of ROP. Two hundred ninety-six infants were randomly assigned to either a constantly monitored (CM) or standard care (SC) group. CM infants had tcPO2 monitored continuously as long as they required supplemental oxygen, whereas SC infants had tcPO2 monitored only during the more acute state of their illness. Management of both groups was otherwise identical. One hundred one of 148 infants in the CM group and 113 of 148 in the SC group survived. The overall incidence of ROP was 51% in the CM group and 59% in the SC group (no significant difference). In infants over 1000 g birthweight, as the weight increased there was increasing risk of developing ROP in the SC group. The odds ratio for the ROPsc:ROPcm reached 7.6 in infants between 1200 and 1300 g in infants with Apgar scores greater than or equal to 8 at 5 minutes. The incidence of cicatricial ROP was similar in both groups: four in the CM and five in the SC group.

An application of multivariate ratio methods for the analysis of a longitudinal clinical trial with missing data.

This paper presents an analysis of a longitudinal multi-center clinical trial with missing data. It illustrates the application, the appropriateness, and the limitations of a straightforward ratio estimation procedure for dealing with multivariate situations in which missing data occur at random and with small probability. The parameter estimates are computed via matrix operators such as those used for the generalized least squares analysis of catetorical data. Thus, the estimates may be conveniently analyzed by asymptotic regression methods within the same computer program which computes the estimates, provided that the sample size is sufficiently computer program which computes the estimates, provided that the sample size is sufficiently large.

The evaluation of Regionalized Perinatal Health Care Programs

A survey, conducted in the summer of 1974, to determine the extent of regionalized perinatal care in the United States revealed 28 states to have programs in operation. Evaluation was a common concern of these programs. A model for the evaluation of Regionalized Perinatal Care Programs is presented here with the North Carolina program used as an example. Evaluation was mandated as an integral component of the program in North Carolina, and this model has been developed in response to that mandate.

Some Further Results for Bivariate Generalizations of the Neyman Type a Distribution

Three bivariate generalizations of the Neyman type A distribuLtion were considered by Holgate [1966], who fitted them to some botanical data by the method of momeents. The type I distribuLtioni is fitted to these data by the methods of maximuLm likelihood anid minimtum chi-squLare and the results compared with the moment estimates. Several recturrence relationis are derived for the three generalizations. These assist in the calculation of the asymptotic varianice covariance matrix that describes the precisioin of the estimates, and results are presented for the type I estimates.

Survey approach to estimating demand for physician assistants

A national probability sample of physicians was surveyed by mail to provide an estimate of the number of job openings for physician assistants (PAs). The responses were used to undertake an empirical analysis of the factors which influence a physicians decision to hire a PA. Estimates were adjusted to account for survey non-response. This approach may be useful for estimating the employment demand for other types of health workers employed by physicians. It was found that in 1976 there was an unconditional demand for 20,338 PAs and a further conditional demand for 3417 PAs. This contrasts sharply with the fact that as a march 1977 only 4845 PAs had graduated from training programs. Approximately 53% of this employment demand was from physicians in the primary care specialties (general/family practice. Obstetrics/gynecology, internal medicine, and pediatrics). Of note was the finding that physicians expected to pay PAs a lower salary than was being received in the market place. Further, 27% of physicians not willing to hire PAs indicated lack of knowledge about them as the main reason for not hiring.

Transcutaneous Oxygen Monitoring and Retinopathy of Prematurity

This study was performed to determine whether the use of continuous tcPO2 monitoring could reduce the incidence of ROP in preterm infants receiving oxygen therapy. Two hundred and ninety-six infants with birth weights less than or equal to 1300 grams were randomly assigned to a continuous monitoring (CM) or a standard care (SC) group. CM infants had tcPO2 monitored continuously as long as they required supplemental oxygen while SC infants had tcPO2 monitored only during the more acute state of their illness. Management of both groups was otherwise identical. One hundred and one of 148 infants in the CM and 113 of 148 patients in the SC groups survived. Mean birth weights and gestational age were similar in both groups. Duration of mechanical ventilation and oxygen therapy was also similar. The overall incidence of ROP was 51% in the CM and 59% in the SC group. As birth weight for infants greater than or equal to 1000 grams increased a higher risk for developing ROP was noted in the SC group. Four infants in the CM and 5 in the SC group developed cicatricial ROP. These results suggest that continuous tcPO2 monitoring may reduce the incidence of ROP in infants with birth weights greater than 1000 grams, but not in the smaller infants in whom this complication occurs more frequently and is more severe.