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Biomedical subjects

P R Freeman

Publications and source records attributed to P R Freeman.

13 recordsLinked to original sources
PubMed1993

The role of p-values in analysing trial results.

The current widespread practice of using p-values as the main means of assessing and reporting the results of clinical trials cannot be defended. Reasons for grave concern over the present situation range from the unsatisfactory nature of p-values themselves, their very common misunderstanding by statisticians as well as by clinicians and their serious distorting influence on our perception of the very nature of clinical trials. It is argued, however, that only by fully understanding the reasons why they have become so universally popular can we hope to change opinion and introduce more sensible ways of summarizing and reporting results. Some of the ways in which this might happen are discussed.

Bayes Theorem↗
PubMed1989

The performance of the two-stage analysis of two-treatment, two-period crossover trials.

In the two-treatment, two-period crossover trial, patients are randomly allocated either to one group that receives treatment A followed by treatment B, or to another group that receives the treatments in the reverse order. Grizzle first proposed a two-stage procedure for analysing the data from such a trial. This paper examines the long-run sampling properties of this procedure, in terms of mean square error of point estimates, coverage probability of confidence intervals and actual significance level of hypothesis tests for the differences between the effects of the two treatments. The advantages of incorporating baseline observations into the analysis are also explored. Because the preliminary test for carryover is highly correlated with the analysis of data from the first period only, actual significance levels are higher than nominal levels even when there is no differential carryover. When carryover is present, the nominal level very seriously understates the actual level, and this becomes even worse when baseline observations are ignored. Increasing sample size only exacerbates the problem since this adverse behaviour then occurs at smaller values of the carryover effect. It is concluded that the two-stage analysis is too potentially misleading to be of practical use.

Analysis of Variance↗
PubMed1989

A comparison of low-dose maintenance treatment with enprostil against ranitidine in the prevention of duodenal ulcer recurrence.

Enprostil, a prostaglandin E2 analogue, is effective in healing acute duodenal ulcer but its value in preventing recurrence, when given daily for maintenance therapy, is uncertain. In this three-centre study we compared enprostil and ranitidine maintenance therapy; the latter is known to reduce duodenal ulcer relapse rates. Patients whose duodenal ulcers had been healed by treatment with an H2-receptor antagonist were randomized to receive single-blind treatment with either 35 micrograms enprostil (n = 64) or 150 mg ranitidine (n = 64) at bedtime for periods of up to 1 year. Endoscopy was routinely performed at 3 months at one centre, and at 6 and 12 months at all three centres, or whenever ulcer symptoms recurred. Clinical assessment and laboratory investigations were performed every 3 months. Relapse, defined as recurrent ulcer with or without pain, or erosions with pain, was significantly greater in patients on enprostil, the comparative rates at 3, 6 and 12 months were: enprostil 23, 31 and 36% ranitidine 6, 12 and 17% (P = 0.013; P = 0.03 and P = 0.03, respectively). Thirty-one patients reported adverse events, the most common being headache (enprostil = 6, ranitidine = 2) and mild diarrhoea (enprostil = 6, ranitidine = 0). Four patients on enprostil were withdrawn for adverse events, although none terminated because of diarrhoea. There were no clinically significant changes in haematology or biochemistry. Enprostil may reduce duodenal ulcer relapse but at a dose of 35 micrograms nightly, it is less effective than 150 mg ranitidine nightly.

Adult↗
PubMed1982

The effects of methadone on the social behavior and activity of the rat.

Pairs of 80-day-old female rats were given SC injections of either 0, 1, 2.5, or 4 mg/kg of methadone hydrochloride on each of 6 days. Both animals of the pair received the same dose. One hour postinjection, each pair was observed in a circular arena for a five minute period during which the following dependent measures were recorded: total time in contact, latency to initial contact, frequency of aggressive grooms, and locomotor activity. The results indicated that the rats treated with methadone spent less time in contact, took longer to contact, and aggressively groomed each other less frequently than rats treated with a saline vehicle. Also, the results suggested that the disruption of social behavior produced by methadone was not a reflection of decreased activity levels.

Aggression↗
PubMed1980

Methadone exposure in utero: effects on open-field activity in weanling rats.

In a 4 group design, pregnant rats were injected with 0, 4, or 16 mg/kg of methadone hydrochloride daily. The fourth group served as a nonhandled, nontreated control. All females in the first three groups were injected from Day 8 to gestation until term. At birth, litters were weighted, culled to eight pups each, and given to other nontreated surrogate mothers. Daily observation was made to determine infant mortality. At Day 28 of age, offspring were weaned, weighed, and separated by sex. Body weights were low at birth among the high methadone offspring and infant mortality was high. By weaning, mortality remained high, although weights were similar to controls. At weaning, high dose offspring showed depressed open-field activity when compared to low dose and control offspring. Methadone appears to cause deficits in behavioral development which can be detected at weaning.

Animals↗