Search PubMed⌕ Search

Biomedical subjects

R B McHugh

Publications and source records attributed to R B McHugh.

At least 19 recordsLinked to original sources
PubMed1989

A reduction factor in goodness-of-fit and independence tests for clustered and weighted observations.

Situations often arise in a large-scale household survey where a complex probability sample of clusters rather than of individuals is drawn from a large population. Typically, the clusters of such complex samples include a number of correlated members. The responses of these members are then weighted to obtain estimates for the population. Such weighted data are commonly published by the National Center for Health Statistics and other U.S. federal agencies. Frequently, problems arise when such data are tested by usual chi-square test statistics for goodness of fit or independence. Researchers have discovered that the usual chi-square tests provide spuriously inflated results when applied to cluster samples and that new methods are required to correct such problems. This paper proposes a strategy for a goodness-of-fit or independence test based on correlated and weighted data arising in cluster samples, and provides a factor that validly reduces the inflation of the usual chi-square statistics. This method is applied to the chronic condition data collected from the St Paul-Minneapolis, Minnesota, primary sampling unit (PSU) during the 1975 National Health Interview Survey (NHIS). This analysis, together with simulation studies presented elsewhere, provides evidence that the usual chi-square statistics from such data can be corrected for the impacts of clustering and weighting by use of the proposed reduction factor.

Analysis of Variance↗
PubMed1984

Confidence estimation and the size of a clinical trial.

The general procedure for sample size determination based upon the confidence interval approach is reviewed and presented for both absolute and relative precision stipulations. The relationship between precision and sample size is discussed and methods for sample size determination for clinical trials are presented and illustrated with numerical examples.

Clinical Trials as Topic↗
PubMed1984

Molar and nonmolar teeth compared over 6 1/2 years following two methods of periodontal therapy.

Limited information is available comparing the relative longitudinal effectiveness with respect to tooth type of scaling and root planing alone and scaling and root planing followed by flap procedures. The purpose of this study was to investigate these treatment methods as applied to molar and nonmolar teeth on a longitudinal basis in humans. Seventeen subjects with chronic periodontitis received thorough scaling and root planning as well as oral hygiene instruction. A modified Widman flap was then randomly performed for one-half of each subject's dentition. Routine recall prophylaxis and oral hygiene reinforcement were administered postsurgically every 3 to 4 months. Pocket depth and clinical attachment levels were recorded by a single calibrated examiner before therapy and at intervals up to 61/2 years following active treatment. Ten subjects remained as participants after 61/2 years. A paired t test was used to test for the mean difference in pocket depth and clinical attachment level between molar and nonmolar teeth for each treatment method. For pockets initially 4 to 6 mm, the results indicated greater pocket depth and more apical clinical attachment level on molars than nonmolars treated by either method of therapy. For pockets initially greater than or equal to 7 mm there was no difference between pocket depth on molar and nonmolar teeth following scaling and root planing alone. However, there was less overall pocket depth on nonmolars than molars following the flap procedure, indicating a greater effect of pocket reduction on nonmolar than molar teeth with the flap procedure. No difference between tooth types was found for clinical attachment level in pockets initially greater than or equal to 7 mm with either treatment method. Both treatment methods resulted in at least maintenance of pretreatment attachment levels adjacent to molar and nonmolar teeth.

Adult↗
PubMed1983

Comparison of surgical and nonsurgical treatment of periodontal disease. A review of current studies and additional results after 61/2 years.

Many well designed clinical studies have established the effectiveness of periodontal therapy. Surgical procedures have been shown to be effective in treating periodontitis when followed by appropriate maintenance care. Scaling and root planing alone have recently been compared to scaling and root planing plus soft tissue surgery in several longitudinal trials. A review of the literature indicates several important findings including a loss of clinical attachment following flap procedures for shallow (1-3 mm) pockets and no clinically significant loss after scaling and root planing. These studies also generally report either a gain or maintenance of attachment level for both procedures in deeper pockets (greater than or equal to 4 mm). For these pockets, neither procedure has been shown to be uniformly superior with respect to attachment gain. All reports indicate that both treatment methods result in pocket reduction. However, the literature also indicates that scaling and root planing combined with a flap procedure results in greater initial pocket reduction than does scaling and root planing alone. This difference in degree of pocket reduction between procedures tends to decrease beyond 1-2 years. It has been shown that both treatment methods result in sustained decreases in gingivitis, plaque and calculus and neither procedure appears to be superior with respect to these parameters. Additional data from the study at the University of Minnesota indicate that similar results are maintained up to 61/2 years following active therapy. Pocket depth did not change for shallow (1-3 mm) pockets treated by either scaling and root planing alone or scaling and root planing followed by a modified Widman flap. For pockets 4-6 mm, both treatment procedures resulted in equally effective sustained pocket reduction. Deep pockets (greater than or equal to 7 mm) were initially reduced more by the flap procedure. After 2 years, no consistent difference between treatment methods was found in degree of pocket reduction. However, as compared to baseline, pocket reduction was sustained to 61/2 years with the flap and only 3 years with scaling and root planing alone. After 61/2 years, sustained attachment loss in shallow (1-3 mm) pockets was found after the modified Widman flap. Scaling and root planing alone in these shallow pockets did not result in sustained attachment loss. For pockets initially 4-6 mm in depth, attachment level was maintained by both procedures but scaling and root planing resulted in greater gain in attachment as compared to the flap at all time intervals.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1981

A randomized four-years study of periodontal therapy.

The purpose of this study was to compare the long term effectiveness of scaling and root planing alone to scaling and root planing followed by periodontal surgery. Seventeen subjects with moderate to advanced periodontitis received through scaling and root planing as well as oral hygiene instruction. A modified Widman flap was then randomly performed for one-half of each subject's dentition. Recall prophylaxis and oral hygiene reinforcement were administered for 4 years after completion of therapy. Shallow crevices (1--3 mm)subjected to either procedure tended to increase slightly in depth and exhibit a slight loss of attachment when compared to pretreatment measurements. Moderately deep pockets (4--6 mm) treated by either procedure were reduced and demonstrated a sustained gain or maintenance of attachment level. Pockets initially greater than or equal to 7 mm exhibited the greatest reduction in depth and attachment gain. Gingivitis was reduced following either procedure for moderate and deep pockets. No difference in supragingival plaque retention was noted and both procedures reduced calculus. The results indicate that both procedures were effective in treating moderate to advanced periodontitis. However, the additional flap procedure tended to result in greater pocket reduction and attachment gain for deeper pockets.

Adult↗
PubMed1980

The Wiskott-Aldrich syndrome in the United States and Canada (1892-1979).

Information was collected on 301 cases of the Wiskott-Aldrich syndrome in the United States and Canada Examination of available medical records, death certificates and published case reports on these patients showed that they came from a wide geographic area and many diverse ethnic and racial groups. No significant difference was found in the incidence of cases born between 1947 and 1976; the overall rate was 4.0 per million live male births in the United States. Median survival has increased with time from eight months for patients born before 1935 to 6.5 years for those born after 1964. Seventy-six of the 301 patients (25%) were still alive at last follow-up and ranged in age from 1 to 36 years with a median of 10 years. Causes of death were primarily limited to infections or bleeding, but malignancy represented a significant problem. Twelve percent of the group (36 of 301) developed malignancy, the predominant types being lymphorecticular tumors (23 of 36) and leukemia (7 of 36). The overall relative risk for malignancy was found to be greater than 100 times that of the general population and was found to increase with increasing age.

Adolescent↗
PubMed1979

The estimation of dental caries incidence in the presence of diagnostic error.

Diagnostic error in large scale screening programs for dental caries is frequent, as when teeth initially classified as carious are later diagnosed as never having been affected by caries. This paper presents a general formulation of diagnostic error in dental caries screening. The basic parameter of the formulation is the caries incidence rate. The general formulation of this paper permits an explicit comparison, in a common notation, of two specific models of diagnostic error--one due to Carlos and Senning, the other to Lu. Each model gives rise to a consistent estimator of the incidence rate. The distributional properties of these estimators had not previously been examined because of the dependence of teeth in the same mouth with respect to caries experience. Using the present formulation, the sampling scheme may be regarded as a one-stage cluster sample with mouths as clusters. This approach accounts for intracluster dependence thus permitting the derivation of an estimator of the relevant covariance matrix and a confidence interval for the incidence rate.

Dental Caries↗
PubMed1977

Radiotherapy in the postoperative treatment of operable cancer of the breast. Part I. Critique of the clinical and biometric aspects of the trials.

A statistical assessment of several "randomized" clinical trials was carried out and the following conclusions were noted. 1. There is no statistically significant evidence that radiation to the peripheral lymphatics and/or chest wall following radical mastectomy affects survival. 2. There is significant evidence that postoperative irradiation to the peripheral lymphatics and/or chest wall does decrease local recurrence rate. 3. There is reliable evidence that the treatment of local recurrence, once it develops, is successful in only 50% of the cases. 4. There is evidence that radiation plus simple mastectomy is as effective in the treatment of breast cancer as radical mastectomy alone. It is our considered opinion that radiation remains a useful adjuvant and complementary agent in the treatment of breast cancer, is not harmful vis a vis survival and should be used when and where indicated.

Adult↗
PubMed1977

Radiotherapy in the postoperative treatment of operable cancer of the breast. Part II. A re-examination of Stjernswärd's application of the Mantel-Haenszel statistical method. Evaluation of the effect of the radiation on immune response and suggestions for postoperative radiotherapy.

A re-examination of the statistical methods used to develop the claim that radiation postoperatively decreases survival was carried out. This study demonstrates that a) when correct figures are used, statistical significance is not demonstrated, i.e. there is not statistically significant evidence that irradiation of the peripheral lymphatics and/or chest wall following mastectomy has a deleterious effect on survival, b) the use of the Mantel-Haenszel procedure was inappropriate for the purpose for which it was used. A survey of the available evidence fails to substatiate the claim that the immunological system effects of local irradiation relate in any way to decreased survival. Recommendations for the use of irradiation postoperatively in the treatment of breast cancer are made.

Adult↗
PubMed1977

Post-hypophysectomy insulin response in patients with advanced breast cancer.

Seven postmenopausal women with metastic breast cancer underwent transsphenoidal hypophysectomy. The rate of disappearance, k*, of iv glucose and insulin following iv glucose and l-arginine infusion was determined before and after the ablation. The k* was estimated with a linear least squares weighted regression method. The insulin secretory capacity of the pancreas before and after the ablation was evaluated with the index of insulinogenic reserve, the index representing the quantity of insulin secreted per unit of glycemic stimulus. Following iv glucose and arginine, there was no significant difference in the mean k* for glucose and insulin, before and after the ablation. The insulinogenic index before was lower than the normal. After hypophysectomy, the index decreased further for the first 30 min following iv glucose. In patients with advanced cancer the index of insulinogenic reserve is lower than normal and is suppressed further by hypophysectomy.

Blood Glucose↗