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V F Flack

Publications and source records attributed to V F Flack.

16 recordsLinked to original sources
PubMed1996

The analysis of incomplete data in the three-period two-treatment cross-over design for clinical trials.

The additional time to complete a three-period two-treatment (3P2T) cross-over trial may cause a greater number of patient dropouts than with a two-period trial. This paper develops maximum likelihood (ML), single imputation and multiple imputation missing data analysis methods for the 3P2T cross-over designs. We use a simulation study to compare and contrast these methods with one another and with the benchmark method of missing data analysis for cross-over trials, the complete case (CC) method. Data patterns examined include those where the missingness differs between the drug types and depends on the unobserved data. Depending on the missing data mechanism and the rate of missingness of the data, one can realize substantial improvements in information recovery by using data from the partially completed patients. We recommend these approaches for the 3P2T cross-over designs.

Analysis of Variance↗
PubMed1996

Relationships between clinician variability and radiographic guidelines.

This study evaluated the replicability of clinical measurements under careful calibration of multiple dentists and how the replicability can relate to their use as selection criteria in guidelines for prescribing dental radiographs. For 48 consenting patients, three dentists clinically examined each patient and recorded the presence of all clinical findings using standardized selection criteria. The examinations were performed independently of each other, but with periodic conferences of the dentists to clarify general measurement criteria. The degree of agreement among the dentists is described by the interrater agreement kappa for several standard clinical indications such as rating of caries, periodontal disease, and tooth mobility. Almost perfect agreement was obtained for tooth status, restoration size, and restoration material. Moderate agreement resulted for measures of caries, defective restoration presence, and gingival recession presence. Only fair agreement was obtained for other periodontal disease measures. The relationship between extent of agreement and guidelines' results was examined for the FDA Guidelines. The differences among the dentists' clinical measurements resulted in considerable differences among the radiographs that were selected by the FDA Guidelines' criteria. Even so, the missed disease rates for 490 patients in a larger study of the FDA Guidelines' efficacy were very low and did not vary greatly among the three dentists. We conclude that guidelines' criteria can be quite robust to variation from dentists' clinical measurement differences, as seen from the FDA Guidelines applied under the idealized setting where the dentists are periodically recalibrated through group discussions of the clinical measurements' definitions and interpretations.

Adolescent↗
PubMed1995

Efficacy of FDA guidelines for prescribing radiographs to detect dental and intraosseous conditions.

OBJECTIVES: This study compared the FDA guidelines for ordering dental radiographs to a conventional full-mouth examination for the detection of intraosseous disease and conditions affecting teeth other than caries. STUDY DESIGN: We examined 490 patients and selected posterior bite-wing and periapical views as indicated by the patient's signs or symptoms. We compared the radiographic findings with the use of this selected set of radiographs to those from a full-mouth set of radiographs to determine the rates of missed disease when the FDA guidelines were used. RESULTS: The most commonly missed intraosseous findings were osteosclerosis, unerupted teeth, periapical radiolucencies, and primary root tips. Periapical radiolucencies that were most probably periapical cemental dysplasia were missed in six patients. The most commonly missed dental findings were resorbed roots and pulp stones. Three instances of dens in dente were missed. CONCLUSIONS: When we used the FDA guidelines, the number of missed intraosseous and dental conditions was small and most likely inconsequential given the range of variability in dental diagnosis and treatment.

Adolescent↗
PubMed1995

Cross-correlation between stress, pain, physical activity, and temporalis muscle EMG in tension-type headache.

Thirty-six tension-type headache subjects and 36 non-headache matched controls recorded their temporalis muscle electromyographic (EMG) activity and their pain intensity, stress and physical activity levels in a daily diary. Measurements were performed every 30 min for 6 days (EMG 3 days only). A time-lagged cross-correlational analysis between pain, stress, physical activity, and EMG shows that the highest correlation coefficient values occurred between pain and stress at the same (r = 0.33) and at the two preceding 0.5 h time points (r = 0.21 and r = 0.26) in the headache group. Virtually no correlation was found between pain, stress, or physical activity with EMG for either group. These data show that temporalis muscle activity levels were not related to the rise and fall of the subjects' pain or stress levels. Conversely, elevated stress appeared to be highly related to pain; it occurs as both an antecedent and simultaneous event with elevated headache pain.

Adolescent↗
PubMed1995

Efficacy of the FDA selection criteria for radiographic assessment of the periodontium.

The diagnosis of periodontitis is generally made on the basis of a clinical examination supported by radiographic evidence of bone loss. Recent guidelines promulgated by the US Food and Drug Administration recommend that periapical radiographs be ordered on the basis of clinical signs and symptoms indicating the probable presence of disease. This study evaluated the effectiveness of the FDA Guidelines for ordering radiographs for new adult dental patients as related to assessment of the periodontal condition of the patient. We examined 490 patients and determined the periapicals needed to supplement the posterior bitewings based upon the patient's clinical findings. We measured the reduction in the number of radiographs ordered as well as the extent of missed alveolar and furcation bone loss resulting from the use of the selected set of radiographs compared with a complete set. Four hundred thirty-three subjects had at least one clinical sign of periodontitis present in their mouths, and 264 demonstrated radiographic evidence of alveolar bone loss. Of the 460 subjects on whom periodontal probing was conducted, two-thirds demonstrated periodontal probing depths in excess of 3 mm; almost half showed evidence of bleeding upon probing. Individuals with clinical signs of periodontitis had, on average, 10 periapicals ordered--more than twice the number as those with no sign of periodontitis. Of the 2,415 teeth with radiographic findings of proximal or furcal bone loss, 152 sites of bone loss (6%) were missed when the selected set of films plus the posterior bitewings was used.

Adolescent↗
PubMed1995

Assessing the FDA guidelines for ordering dental radiographs.

In 1988, the U.S. Food and Drug Administration issued guidelines to help dentists reduce the amount of X-ray exposure to patients without reducing the quality of care. This study assesses the efficacy of those guidelines. The authors examined 490 patients and ordered radiographs as indicated by the FDA guidelines. Using the guidelines, they ordered a mean of 9.7 radiographs out of a 17-film series, a reduction of 43 percent compared with a full-mouth series. The authors conclude that dentists can reduce a patient's exposure to X-rays by using these guidelines with a low level of missed radiographic findings, most of which would have no effect on the patient's treatment.

Adolescent↗
PubMed1994

Efficacy of FDA guidelines for ordering radiographs for caries detection.

This study evaluated the effect on caries diagnosis of using the Food and Drug Administration (FDA) guidelines for ordering radiographs on a sample of new adult patients seeking general dental care at a dental school clinic. These guidelines recommend posterior bitewing views accompanied by supplemental periapical views as indicated by the patient's clinical signs or symptoms. We compared the findings from the use of this protocol to those from a full-mouth set of radiographs made on the same new patient. We examined 490 patients and ordered periapical radiographs in accordance with the FDA guidelines, namely, when there was some clinical sign or symptom suggesting the need for radiographs. A full-mouth set of radiographs was obtained, and both the full and selected sets were evaluated separately. We found that 95% of our patients had one or more carious lesions, with an average of 5.7 carious teeth per patient. Of the 2808 carious teeth detected in the study, 1949 (69%) were found radiographically and 1564 (56%) were found clinically. Indeed, 1244 (44%) of the carious teeth were detected only by radiographic examination. Use of the FDA guidelines resulted in a 43% reduction in the number of radiographs ordered. Reduction in the number of images made on patients resulted in failure to detect 93 lesions (3.3%) located on 88 teeth in 11.4% of the study patients. Most of the missed lesions (2.9%) were radiographically confined to the enamel of anterior maxillary teeth. Only 36 of the missed lesions (1.6% of all radiographic lesions) extended into the dentin. We believe that this number is very small and most likely inconsequential compared with the considerable diversity among dentists regarding radiographic detection of caries, as well as the diversity of opinion regarding the indications for restorative treatment.

Adolescent↗
PubMed1993

Sample size determinations using logistic regression with pilot data.

Suppose the goal of a projected study is to estimate accurately the value of a 'prediction' proportion p that is specific to a given set of covariates. Available pilot data show that (1) the covariates are influential in determining the value of p and (2) their relationship to p can be modelled as a logistic regression. A sample size justification for the projected study can be based on the logistic model; the resulting sample sizes not only are more reasonable than the usual binomial sample size values from a scientific standpoint (since they are based on a model that is more realistic), but also give smaller prediction standard errors than the binomial approach with the same sample size. In appropriate situations, the logistic-based sample sizes could make the difference between a feasible proposal and an unfeasible, binomial-based proposal. An example using pilot study data of dental radiographs demonstrates the methods.

Confidence Intervals↗
PubMed1993

The reproducibility and validity of a self-administered semiquantitative food frequency questionnaire in subjects from South Dakota and Wyoming.

Most validation studies of food frequency questionnaires have been done in populations capable of reporting their diet with unusual accuracy. In this study of ranchers and subjects selected at random, we compared nutrient intakes as assessed with multiple diet records with those assessed with a self-administered food frequency questionnaire (the Harvard-Willett instrument with 116 food items). One hundred thirty-eight subjects from South Dakota and Wyoming, 64 males and 74 females, completed at least one food frequency questionnaire and multiple 1-day diet records (mean = 5 days) during a 6-month to 1-year period. Of invited subjects, 88% participated; 59% of participants had a high school education or less. For 22 dietary nutrients (excluding supplements) and alcohol, the median crude correlation between intakes based on diet records and the food frequency questionnaire completed before the diet records was 0.42; after adjustment for energy, age, and sex, and after correction for attenuation in the correlation coefficients due to error from a limited number of diet records, the median correlation was 0.52. Correlations for men and women were similar. The validity of the food frequency questionnaire in this population was similar to that reported previously and supports the use of self-administered food frequency questionnaires in studies of general populations.

Data Collection↗
PubMed1993

Reproducibility of examiner performance for muscle and joint palpation in the temporomandibular system following training and calibration.

The purpose of this investigation was to assess examiner ability to consistently perform specific tasks related to muscle and joint palpation. Four trained and calibrated examiners were asked 1) to deliver index finger pressures within a high (1.5-2.1 kg) and low (0.5-1.1 kg) target pressure range and 2) to precisely locate one joint palpation and four muscle sites. After passing a calibration test, the performance of the examiners was monitored during the course of a replicability study assessing the consistency of clinical findings during repeated exams for TM disorders. (1) Index finger pressure was regularly tested over a 3-month period with a hand held pressure algometer, and the reading of each trial was recorded. Data analysis showed a high proportion of trials within the pressure range (overall 89.5%). Examiner performance across target range of pressures was statistically different for success rate and mean pressure delivered. The differences in the mean finger pressure delivered by each examiner (intraexaminer variation) was low and varied from 0.12 to 0.22 kg/cm2 for the desired range of pressures. (2) Paired examiners were asked to independently and sequentially mark palpation sites over the forehead, superficial and deep masseter, anterior temporalis, and lateral capsule of the temporomandibular joint. Replicability of site locations was assessed by measuring, with a boley gauge, the distance between sites selected by the paired examiners. Except for the superficial masseter and the anterior temporalis, the paired examiners selected palpation sites within a distance of 7 mm more than 85% of the time.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Screening for psychological problems in temporomandibular disorder patients.

Research efforts have been directed to determine whether temporomandibular disorder (TMD) patients have psychological problems and whether these factors influence treatment outcome. Because there is no consensus about the best way to quickly assess psychological problems in TMD patients, this study was designed to evaluate a simple method for identifying psychological factors that may need to be addressed as part of a comprehensive treatment program. This method involved having TMD patients systematically rate themselves, using a brief screening questionnaire, for the presence or absence of psychological problems. These ratings were then compared to results from extensive psychological testing. Sensitivity, specificity, and ordinal rank-based association model analyses showed moderate to strong associations between patients' ratings and the corresponding psychometric measures. These results provide evidence that the brief self-ratings of psychological factors utilized in this study may be a useful first step to screening for psychological difficulties in TMD patients.

Adult↗
PubMed1989

Dentists' ability to detect psychological problems in patients with temporomandibular disorders and chronic pain.

Do patients with temporomandibular disorders (TMD) have significant psychosocial problems? Research efforts have sought to determine if these problems exist, and if so, how they influence treatment outcome. Even when psychosocial factors do influence treatment outcome, identifying them by formal psychological tests can be time consuming and costly. Dentists' impressions of the psychological status of these patients were tested to determine if they are an effective method for screening psychological factors thought to influence treatment outcome. The results suggested that a screening procedure based on dentists' impressions from an initial examination do not adequately identify psychological problems in patients with TMD.

Adult↗
PubMed1987

Rehabilitation needs and breast cancer: the first month after primary therapy.

Breast cancer is the most common neoplasm in occidental women, yet very little information is available about the rehabilitation needs of these patients. This report reviews in detail the physical, psychological, social, and financial problems identified by fifty women during the first month after primary surgical treatment. The most frequently reported problems were physical and psychological. Patients undergoing modified radical mastectomy (MRM) are compared with patients receiving segmental mastectomy and primary radiotherapy (SM). There were few differences between the two surgical treatment groups; however, patients in the MRM group reported more difficulty with clothing and body image, while the SM group had more disruption of recreation and social activities. Information about the rehabilitation problems of patients with this common neoplasm should be helpful to patients and to the members of the health care team who are helping them recover.

Adult↗