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Biomedical subjects

N J Birkett

Publications and source records attributed to N J Birkett.

At least 19 recordsLinked to original sources
PubMed1995

Validation of a food habits questionnaire: poor performance in male manual laborers.

OBJECT: To examine the reliability and validity of a food habits questionnaire developed by Kristal et al in male manual laborers. DESIGN: A cross-sectional baseline survey. SETTING: The community of Ottawa-Carleton, Canada. SUBJECTS: All people working in non-office-based positions for two local governments were invited to a heart-health screening clinic. Male subjects (n = 362) who met risk factor eligibility criteria were interviewed and entered into the study. MAIN OUTCOME MEASURES: The food habits questionnaire developed by Kristal et al was the main focus of analysis. Additional outcomes included a food frequency questionnaire and risk factors for cardiovascular disease. STATISTICAL ANALYSES: Reliability was assessed using Cronbach's alpha and Pearson correlation coefficients; confirmatory factor analysis was also done. Validity assessment included partial correlations. RESULTS: Low internal consistency was found for the five subscales of the questionnaire (alpha = .13 to .53). Confirmatory factor analysis did not reveal the postulated five-factor (subscale) structure. Correlation of the subscale scores with dietary fat intake was low (r = -.09 to -.23), and none of these associations were statistically significant after adjustment for age, body mass index, and education. An alternative scoring system that treated the questionnaire as a unidimensional behavioral checklist produced a higher internal consistency (alpha = .70) and significant correlation with dietary fat intake (r = -.27). CONCLUSIONS: The psychometric properties and scoring of the food habits questionnaire need to be explored in additional populations before the questionnaire is adopted for general use.

Adult↗
PubMed1995

Self-measurement of blood pressure: issues related to the training of patients. Canadian Coalition for High Blood Pressure Prevention and Control.

For effective self-measurement of blood pressure, patients need to be able to obtain accurate and reproducible measurements. Criteria for measuring blood pressure have been well developed in research studies, and through the use of standardized training programs it has been established that nonmedically trained individuals can obtain valid measurements. These recommendations for blood pressure measurement were adapted to the self-measurement situation. Either manual sphygmomanometers or automated electronic devices can be used effectively. Although automated devices may be easier to use, the health care practitioner should ensure that any such device has been demonstrated to be accurate and reliable before its adoption. There are no reported programs available for training individuals in the use of self-measurement. A check-list has been developed for use by health care practitioners. It is estimated that proper training will usually take more than 20 mins. Since many health care practitioners do not use the recommended blood pressure measurement technique, there is also a need to develop programs to 'train the trainers'. Finally, individuals undertaking regular self-measurement should have their technique and the calibration of their instruments checked at regular intervals (six to 12 months).

Blood Pressure Determination↗
PubMed1995

Self-measurement of blood pressure: recommendations of the Canadian Coalition for High Blood Pressure Prevention and Control.

OBJECTIVE: To provide health care professionals with guidelines on the use of blood pressure self-measurement. METHODS: Recommendations were devised after consideration of expert reviews and guidelines, personal files, international standards documents, personal communication with investigators and the results of a MEDLINE search (1966-94) using the term 'blood pressure determination'. BENEFITS, HARMS, COSTS: Self-measurement of blood pressure can be used to detect white coat hypertension, monitor changes in blood pressure closely, more rapidly achieve desired blood pressure goals, increase adherence to antihypertensive therapy and improve patient self-reliance. However, self-measured blood pressure readings may be misleading because there is insufficient normative, prognostic and outcome data and because some patients may not take accurate measurements. The use of self-measurement of blood pressure has a relatively small direct cost and may result in an overall reduction in treatment costs. RECOMMENDATIONS: Self-measured blood pressure readings can be a valuable supplement to clinic (or office) blood pressure readings. However, self-measurement is appropriate neither for patients who are physically or mentally incapable of accurate assessment and interpretation of readings nor for those who do not want to participate. Patients who self-monitor blood pressure require careful training in blood pressure measurement and instruction on the recording and interpretation of blood pressure readings. Advice to patients using monitoring equipment must take into account the needs and abilities of the patient. Although only a few electronic devices for the self-measurement of blood pressure have met recommended performance standards, their use may be more appropriate for some patients and the training requirements fewer than if manual devices are used. VALIDATION: The guidelines of several expert groups were examined in the preparation of these recommendations. The recommendations were presented at the World Conference on Hypertension Control in 1995 and were reviewed by the parent societies of the Canadian Coalition for High Blood Pressure Prevention and Control.

Blood Pressure Determination↗
PubMed1994

Potential problems with the random-zero sphygmomanometer.

The random-zero sphygmomanometer is frequently used in epidemiologic and clinical research to increase the reliability and validity of blood pressure readings. However, recent reports have suggested that there is a correlation between the zero values of a random-zero sphygmomanometer and the zero-corrected blood pressure readings obtained. The design of the random-zero sphygmomanometer would suggest that the zero values and zero-corrected blood pressures should be uncorrelated. Hence, residual correlation might be of importance in determining the utility of this device. We have explored this relation in the Middlesex County Blood Pressure Survey, which collected data on 2725 randomly selected adults. Each person had three blood pressure readings taken with a random-zero sphygmomanometer operated by trained interviewers. There was a very weak but statistically significant correlation between the zero values and zero-corrected systolic blood pressure (r = .034, regression slope = -.10), but there was no statistically significant relation with zero-corrected diastolic blood pressure (r = .0003, slope = .0006). Both the correlations and regression slopes were higher for subjects over age 65 years. These data fail to confirm the observed correlations found by Kronmal et al. This discrepancy might be explained by differences in measurement technique, which could introduce a blood pressure-dependent skewing of the range of zero values. If confirmed, this effect would have no effect on the validity of the final blood pressure readings and hence would not need to be considered in decisions about the use of the random-zero sphygmomanometer.

Adult↗
PubMed1992

Effect of nondifferential misclassification on estimates of odds ratios with multiple levels of exposure.

Nondifferential misclassification of exposure status with a dichotomous exposure will produce biased estimates of odds ratios such that the misclassified odds ratio is always biased toward the null value. However, when an exposure classification has more than two levels, empirical data indicate that the direction of bias is less predictable. Analysis of an algebraic model of multi-level exposure misclassification reveals that all odds ratios based on the misclassified data are constrained between the nonmisclassified odds ratio for the most extreme category and the inverse of this value. This implies that the misclassified odds ratio for the most extreme exposure level will be biased toward the null but that odds ratios for intermediate levels of exposure could be biased away from the null value. Further, the amount of bias depends not only on the misclassification rates but also on the distribution of subjects across exposure levels. If it is assumed that misclassification is likely to occur only between adjacent categories, the range of possible misclassified odds ratios is reduced but is still sufficient to permit serious distortion of an exposure-response relation. In general, biases away from the null occur only for intermediate levels of exposure. Reversal of an exposure-response relation is more likely to occur when misclassification rates are high (especially between nonadjacent levels) and when the number of exposure levels is low.

Bias↗
PubMed1989

A tool for assessing inadequate dialysis.

Blood urea nitrogen (BUN) is thought to be a useful marker of the concentration of other solutes that underly the manifestation of uremia. By monitoring quality assurance parameters, 8 out of 57 dialysis patients were found during monthly blood work exams to have BUN greater than 100 mg/dl. An "Inadequate Dialysis Checklist" was designed for hemodialysis and peritoneal dialysis and used to assess all eight patients' treatments. The dialysis was corrected or integrally modified. As a result, the number of patients with BUN greater than 100 mg/dl decreased. These checklists can be useful for case managers to assess and evaluate dialysis variables.

Blood Urea Nitrogen↗
PubMed1989

Payment for deliveries in Sierra Leone.

The type and amount of payment for deliveries were investigated in 1982 during a survey on health status in two districts. Data on the payments made for 83.5% of the 2591 deliveries in 535 randomly selected study villages showed that the most common method of payment was in cash only. Payments in kind were mostly given to trained traditional birth attendants (TBAs) (for 38.1% of their deliveries) and rare for professional staff (2.9% of deliveries). The total amount paid for a delivery differed significantly with the type of birth attendant (P less than 0.00001) and the place of delivery (hospital, peripheral health unit or home) (P less than 0.00001). The total average payment for a delivery was highest for professional birth attendants (Le 16.60) and lowest for untrained TBAs (Le 4.85) (Le 2 = approx. US+ 1 at the time of the study). The outcome of a delivery had a significant effect on the amount paid. Payments were significantly higher for stillbirths than for live births among professional and auxiliary birth attendants (P less than 0.0001). However, the trained and untrained TBAs received less payment for stillbirths (Le 2.25) than for live births (Le 4.89) (P = 0.0146). The results show that there are several levels of financial disincentives for pregnant women requiring the services of trained auxiliary or professional health workers at the time of delivery.

Cross-Sectional Studies↗
PubMed1988

Evaluation of diagnostic tests with multiple diagnostic categories.

The evaluation of diagnostic tests attempts to obtain one or more statistical parameters which can indicate the intrinsic diagnostic utility of a test. Sensitivity, specificity and predictive value are not appropriate for this use. The likelihood ratio has been proposed as a useful measure when using a test to diagnose one of two disease states (e.g. disease present or absent). In this paper, we generalize the likelihood ratio concept to a situation in which the goal is to diagnose one of several non-overlapping disease states. A formula is derived to determine the post-test probability of a specific disease state. The post-test odds are shown to be related to the pre-test odds of a disease and to the usual likelihood ratios derived from considering the diagnosis between the target diagnosis and each alternate in turn. Hence, likelihood ratios derived from comparing pairs of diseases can be used to determine test utility in a multiple disease diagnostic situation.

Bayes Theorem↗
PubMed1988

Computer-aided personal interviewing. A new technique for data collection in epidemiologic surveys.

Most epidemiologic studies involve the collection of data directly from selected respondents. Traditionally, interviewers are provided with the interview in booklet form on paper and answers are recorded therein. On receipt at the study office, the interview results are coded, transcribed, and keypunched for analysis. The author's team has developed a method of personal interviewing which uses a structured interview stored on a lap-sized computer. Responses are entered into the computer and are subject to immediate error-checking and correction. All skip-patterns are automatic. Data entry to the final data-base involves no manual data transcription. A pilot evaluation with a preliminary version of the system using tape-recorded interviews in a test/re-test methodology revealed a slightly higher error rate, probably related to weaknesses in the pilot system and the training process. Computer interviews tended to be longer but other features of the interview process were not affected by computer. The author's team has now completed 2,505 interviews using this system in a community-based blood pressure survey. It has been well accepted by both interviewers and respondents. Failure to complete an interview on the computer was uncommon (5 per cent) and well-handled by paper back-up questionnaires. The results show that computer-aided personal interviewing in the home is feasible but that further evaluation is needed to establish the impact of this methodology on overall data quality.

Blood Pressure↗
PubMed1988

Caffeine-containing beverages and the prevalence of hypertension.

Caffeine can produce a mild hypertensive effect for a few hours after use. Some epidemiological data relate chronic coffee intake to an increased risk of cardiovascular disease. We explored the possibility that a regular intake of caffeine-containing beverages (tea, coffee, cola) might produce a chronic increase in blood pressure and increase the likelihood of developing sustained hypertension. A random population survey of 2436 adults was made, with standardized blood pressure readings and a food-frequency questionnaire to determine the regular intake of various nutrients. We found evidence that caffeine intake was positively related to an increased diastolic blood pressure but the effect was small (less than 1 mmHg at usual caffeine intake). There was no evidence that a regular caffeine intake increases the risk of being classified as hypertensive.

Age Factors↗
PubMed1987

Assessing hypertension control in the community: the need for follow-up measurements to ensure clinical relevance.

In community surveys of hypertension control the diagnosis is often based on blood pressure measurements taken on only one visit. The clinical diagnosis of hypertension requires demonstration of sustained blood pressure elevation. We conducted a survey that contrasted the results of these two approaches to determining the prevalence of hypertension and the extent to which hypertension is detected and treated. A multistage random sample of 2737 people was selected, examined and interviewed on up to three occasions. Rates of hypertension prevalence and control were computed from data from one, two and three visits. The prevalence of hypertension was overestimated by 30% when the diagnosis was based on data from one rather than three visits, the rates being 149 and 115/1000. The prevalence of undetected hypertension was overestimated by 350%, the rates being 27 and 6/1000. The proportion of subjects with controlled hypertension was underestimated by 23%, at 56%, compared with 73%. These results confirm the need for follow-up measurements to provide a valid assessment of hypertension control in the community.

Adolescent↗
PubMed1987

Factor VIII concentrate for hemophilia: comparison of two heat-treated products.

In a controlled trial of heat-treated factor VIII concentrate from Cutter Laboratories and from Connaught Laboratories Limited, 25 patients with hemophilia received Cutter factor VIII and 24 patients with hemophilia received Connaught factor VIII. The mean increase in factor VIII level was similar for the two products (1.88% and 1.98% per unit/kg of body weight respectively [p greater than 0.1], or 89% and 95% respectively of the expected increase [p greater than 0.1]). In-vivo survival (the duration of factor VIII in the circulation) was compared after seven infusions of each product. The mean half-disappearance times were 10.7 and 9.1 hours respectively (p = 0.1), and the mean biologic half-lives were 11.6 and 9.9 hours respectively (p = 0.04); the clinical significance of the latter difference is dubious. Both products could be reconstituted satisfactorily from the dried state. Two subjects experienced relatively minor side effects following infusion of one lot of Cutter factor VIII. Individual responses to both products showed considerable variation. Therefore, when it is critical to attain predetermined levels of factor VIII, such as before and after surgery, factor VIII assays should be performed to check the patient's response.

Acute Disease↗
PubMed1986

Hypertension control in two Canadian communities: evidence for better treatment and overlabelling.

We evaluated the prevalence and control of hypertension in two Canadian cities without university medical centre facilities. A stratified multistage probability sample was selected, and we interviewed 6258 adults between the ages of 30 and 69 inclusive. Blood pressure measurements were obtained during home interviews. Up to two further visits were made to people with untreated blood pressure elevation. By a diagnostic criterion of 90 mmHg, the hypertension prevalence was 114/1000. Six per cent of the hypertensives were undetected, 6% detected but untreated, 17% treated but uncontrolled and 70% were being treated and controlled. Control was better in females and older subjects. These findings show no disadvantages to hypertensives living away from university medical centres. We found a hypertension prevalence of 143/1000 among people who reported being diagnosed as hypertensive but who had normal blood pressure while not on medication. These results suggest a problem with over-labelling of hypertensives.

Adult↗