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PubMed2006

The impact of different blood sampling methods on laboratory rats under different types of anaesthesia.

Rats with implanted telemetry transponders were blood sampled by jugular puncture, periorbital puncture or tail vein puncture, or sampled by jugular puncture in carbon dioxide (CO2), isoflurane or without anaesthesia in a crossover design. Heart rate, blood pressure and body temperature were registered for three days after sampling. Initially blood pressure increased, but shortly after sampling it decreased, which led to increased heart rate. Sampling induced rapid fluctuations in body temperature, and an increase in body temperature. Generally, rats recovered from sampling within 2-3 h, except for rats sampled from the tail vein, which showed fluctuations in body temperature in excess of 30 h after sampling. Increases in heart rate and blood pressure within the first hours after sampling indicated that periorbital puncture was the method that had the largest acute impact on the rats and that it might take an extra hour to recover from it. CO2 anaesthesia seemed unable to prevent the increase in blood pressure and the fluctuations in body temperature induced by blood sampling, and up to 10 h after sampling, the rats were still affected by CO2 anaesthesia. Rats anaesthetized with isoflurane showed lower increases in blood pressure after, and fewer fluctuations in body temperature during sampling, and the post-anaesthetic effects of isoflurane, if any, seemed to disappear immediately after sampling. It is, therefore, concluded that blood sampling in rats by jugular puncture seems to be the method from which rats most rapidly recover when compared with periorbital puncture and tail vein puncture, and that for anaesthesia, isoflurane is recommended in preference to CO2.

Anesthesia, Inhalation↗
PubMed2005

Evaluating whole genome amplification via multiply-primed rolling circle amplification for SNP genotyping of samples with low DNA yield.

The amount of available DNA is often a limiting factor in pursuing genetic analyses of large-scale population cohorts. An association between higher DNA yield from blood and several phenotypes associated with inflammatory states has recently been demonstrated, suggesting that exclusion of samples with very low DNA yield may lead to biased results in statistical analyses. Whole genome amplification (WGA) could present a solution to the DNA concentration-dependent sample selection. The aim was to thoroughly assess WGA for samples with low DNA yield, using the multiply-primed rolling circle amplification method. Fifty-nine samples were selected with the lowest DNA yield (less than 7.5 microg) among 799 samples obtained for one population cohort. The genotypes obtained from two replicate WGA samples and the original genomic DNA were compared by typing 24 single nucleotide polymorphisms (SNPs). Multiple genotype discrepancies were identified for 13 of the 59 samples. The largest portion of discrepancies was due to allele dropout in heterozygous genotypes in WGA samples. Pooling the WGA DNA replicates prior to genotyping markedly improved genotyping reproducibility for the samples, with only 7 discrepancies identified in 4 samples. The nature of discrepancies was mostly homozygote genotypes in the genomic DNA and heterozygote genotypes in the WGA sample, suggesting possible allele dropout in the genomic DNA sample due to very low amounts of DNA template. Thus, WGA is applicable for low DNA yield samples, especially if using pooled WGA samples. A higher rate of genotyping errors requires that increased attention be paid to genotyping quality control, and caution when interpreting results.

DNA↗
PubMed1986

Does effort play a role in the effect of response requirements on delayed matching to sample?

The possible role of "effort" in the accuracy of pigeons' performance on a delayed matching-to-sample procedure was investigated by examining the effects of response requirements that accompanied a trial-initiating stimulus and that accompanied a sample stimulus. In the first experiment, the effect of varying the size of a fixed-ratio requirement for responses during an initiating stimulus was compared to that of varying a similar requirement for responses during the sample stimulus. Accuracy increased reliably with increases in the ratio scheduled during the sample stimulus, but was not significantly affected by increases in the ratio scheduled on the key during the initiating stimulus. In another phase of Experiment 1, sample duration was held constant while the ratio requirement was varied during the initiating stimulus. Again, accuracy of matching to sample was not significantly affected by the size of the ratio scheduled during the initiating stimulus. Experiment 2 provided a systematic replication of these results in another group of pigeons and included a more detailed analysis of responding. These results support the view that increases in sample-response requirement facilitate accuracy of delayed matching by increasing the durations of exposure to the sample stimuli, and do not support a role of effort in the sample-response effect. In Experiment 3, the facilitative effect of responses on the sample but not of those on the initiating stimulus was replicated using a simultaneous matching-to-sample procedure. This finding provides further evidence against an interpretation of response-requirement effects that appeals to effort; the finding also suggests that sample exposure might affect initial discrimination of the sample rather than remembering the sample.

Animals↗
PubMed2001

Reactivity of serum samples of dogs and horses tested by use of class-specific recombinant-based enzyme-linked immunosorbent assays for detection of granulocytic ehrlichiosis.

OBJECTIVE: To test serum samples of dogs and horses by use of class-specific recombinant-based ELISA for establishing a diagnosis of granulocytic ehrlichiosis attributable to infection with organisms from the Ehrlichia phagocytophila genogroup. SAMPLE POPULATION: Serum samples from 43 client-owned dogs and 131 horses (81 with signs of acute illness and 50 without signs of disease). PROCEDURE: Serum samples were analyzed, using ELISA with a recombinant 44-kd protein antigen for IgM and IgG antibodies to the human granulocytic ehrlichiosis (HGE) agent (NCH-1 strain). Western blot analyses, using infected human promyelocytic leukemia cells, were conducted on 38 serum samples of horses and 11 serum samples of dogs to verify reactivity to the 44-kd peptide. RESULTS: IgM or IgG antibodies to the HGE agent were detected in 5 to 28% of dog serum samples and 5 to 37% of horse serum samples. Thirty-five of 38 (92%) horse serum samples had corresponding results on both tests (2 positive results for 26 samples and 2 negative results for 9 samples), using an ELISA for IgG antibodies or immunoblotting for total immunoglobulins. All 11 serum samples of dogs had positive results for both methods. CONCLUSION AND CLINICAL RELEVANCE: These ELISA with recombinant 44-kd antigen are suitable for detecting IgM or IgG antibodies to the HGE agent in serum samples of dogs and horses. Positive results for serum samples of horses from Connecticut, New York, Virginia, and Georgia indicate that the HGE agent is widely distributed in tick-infested areas of the eastern United States.

Animals↗
PubMed2003

Characterization of season and sampling method effects on measurement of forage quality in fescue-based pastures.

Information on seasonal changes and effects of sampling methods on the measurement of forage quality is limited for fescue-based pastures. Eight continuously grazed, 0.76-ha, fescue-based pastures were used to compare forage type, method of collection, and seasonal effects on forage quality in a repeated-measures, split-plot design. Four pastures were interseeded with red clover in March 2000. Masticate (M; from four ruminally cannulated steers) and hand--clipped (C) samples were collected every 28 d from April to October 2000. Interseeding red clover did not affect (P > 0.10) OM, CP, NDF, and ADF concentrations or CP degradability. Sampling method and season interacted (P < 0.03) for OM, CP, NDF, and ADF concentrations. Concentrations of OM averaged 5 percentage units more (P < 0.01) in C than in M in all months and were more variable with M than with C. Samples clipped between April and September averaged 5.5 percentage units greater NDF (P < 0.01), 3.0 percentage units greater ADF (P < 0.01), and 4.5 percentage units less CP (P < 0.01) than masticate samples obtained during the same time period. Fiber and CP concentrations did not differ (P > 0.10) between C and M samples obtained in October. Differences in CP degradability estimates (using Streptomyces griseus protease) between the two sample types were greater in late-season samples than in samples obtained from April to June. When S. griseus protein degradability estimates were compared with in situ estimates for masticate samples, no differences (P > 0.10) were detected early in the season (April to June). However, the S. griseus procedure overestimated in situ values (P < 0.01) by an average of 3 percentage units in samples obtained between July and October. Differences in composition of C and M samples were substantial until late season, when opportunities for selective grazing were minimal. Small differences between S. griseus and in situ estimates of CP degradability indicate that the S. griseus procedure can yield useful CP degradability estimates for fescue-based pasture samples. Although it might be possible to apply correction values to clipped samples to estimate CP and fiber concentrations of diets selected by grazing cattle, inconsistent relationships preclude this approach for estimates of CP degradability.

Animal Feed↗
PubMed2000

Use of PCR for the detection of genital Chlamydia trachomatis infection on self-obtained mailed vaginal samples.

BACKGROUND: To determine whether the patient self-obtained and mailed vaginal sample might be used for the detection of genital C. trachomatis infection by the PCR. METHODS: Women with genital symptoms, younger than 35 years of age and sexually active were enrolled. Cervical and urethral samples collected by the physician were tested by PCR and cell culture. Three vaginal samples were collected: the first and second - by the physician and the patient at the time of the visit to the clinic. The third vaginal sample was collected by the patient at home and posted dry to the laboratory. All vaginal samples were PCR-tested, including also the internal control for the detection of the inhibitors. RESULTS: The prevalence of chlamydial infection was 19.2%. C. trachomatis was detected in the cervix of 18.5%, in the urethra of 4.4% and in the vagina of 19.2% of the women, when all vaginal samples were considered. Each separate vaginal sampling detected 88.8% of the C. trachomatis infected women. Nearly 10% of the cervical, 3% of the urethral and 12-19% of the vaginal samples were inhibitory. Inhibitors were destroyed by storage of the samples for five days at +4 degrees C or the dilution at 1:10. CONCLUSIONS: Self-collected and mailed vaginal sample is convenient for the patient and useful for the PCR-testing for genital C. trachomatis infections. Sensitivity of sampling might improve if several consecutive samples were to be collected. This self-sampling approach would help to reach section of the population in which pelvic examination and cervical sampling is not routinely performed.

Adult↗
PubMed2001

Comparison of sampling methods for obtaining accurate coagulation values in hemodialysis patients with heparinized central venous catheters.

Monitoring coagulation values in hemodialysis (HD) is integral to the care of patients with central venous catheters (CVCs) to maintain catheter patency. HD patients can have problems providing blood samples and may experience discomfort with venipuncture, but no consensus in the literature is available to identify a reliable and efficient method of obtaining an international normalization ratio (INR) value from a heparinized CVC line. This was a comparative study of three different methods of blood sampling for INR values. The INR samples were obtained from a peripheral venipuncture site, the CVC line, and the arterial bloodline sample port. The peripheral INR sample was used as the gold standard. The study occurred in a 60-station hemodialysis center in a 428-bed, urban, acute care hospital. The sample included 33 HD patients with patent dialysis CVC lines. Blood samples were drawn with a standardized protocol during one HD session from each of the three sites. The Pearson correlation coefficient for the peripheral sample versus the CVC line sample was 0.97 (p < 0.001) and was 0.99 (p < 0.001) between the peripheral sample and the arterial bloodline sample. Results revealed that both alternative methods are suitable for taking INR samples. As a result of this study, the arterial bloodline sample port method for INR sampling was introduced into the HD unit at this hospital. This method has proven to be simple, quick, accurate, and noninvasive to renal patients.

Adolescent↗
PubMed2002

How does the age of a blood sample affect it's activated clotting time? Comparison of eight different devices.

Monitoring activated clotting time (ACT) during extracorporeal procedures is virtually universal. The ACT test is usually performed immediately following blood collection. However, certain situations may occur that delay rapid measurement. It is unknown how an aged blood sample affects the ACT measurement. It is hypothesized that the ACT will be affected as a blood sample ages. Multiple blood samples were taken from six patients undergoing cardiopulmonary bypass (CPB). Samples were divided into two groups, heparinized (H) and unheparinized (UH). ACT/HMT tests were performed with each sample on eight devices (Array Actalyke, Gem PCL, Hemochron Jr. Signature, Hemochron Response, Hemochron 801, Hemotec HMS, Rapidpoint Coag, and Sonoclot II) at three different sample ages [< 60 s (fresh blood), 10 min, and 15 min after sample collection. ACT/HMT results of aged samples (10 min and 15 min after sample collection] were compared to ACT/HMT results for fresh blood using a repeated measures analyses of variance (ANOVA) with Student's-Newman-Keuls post hoc test. In the unheparinized group, no device produced an ACT significantly different from the fresh sample counterpart at the 10 min time point. At the 15 min time point, the Hemochron 801 produced a significantly lower average ACT when compared to the fresh sample. (120 +/- 25 vs. 135 +/- 5 s). In the heparinized group, the Actalyke device produced results with 10 and 15 min aged blood that were significantly longer than fresh blood sample results (ACT < 60 s = 426 +/- 66, 10 min = 457 +/- 82, 15 min = 450 +/- 68 s, p < .05). No other device produced significant differences for either time period. Based on this limited sample population, it seems that accurate ACT may be performed on blood samples up to 15 min old in many devices.

Blood Coagulation Tests↗
PubMed2005

Preliminary evaluation of a cervical self-sampling device with liquid-based cytology and multiparameter molecular testing.

OBJECTIVE: To compare the collection of a liquid-based cell sample using a cervical self-sampling device and traditional sampling using cytologic and molecular-based tests. STUDY DESIGN: This study evaluated the sampling efficiency of the Fournier Cervical Self-Sampling Device (BPG, LLC, Miami, Florida) with regard to overall cell volume of the sample, cytologic diagnoses Path, TriPath Imaging, Burlington, North Carolina) and molecular-based tests for Chlamydia, Gonorrhoeae and human papillomavirus (Hybrid Capture 2, Digene Corp., Gaithersburg, Maryland). Paired samples were blinded and prepared using the SurePath method. RESULTS: The self-collected samples showed an overall increase in cellularity when compared to the cellularity of samples obtained from traditional sampling. Cytologic results were comparable for the 2 sampling methods. The self-sampling device showed greater sensitivity with regard to molecular-based human papillomavirus testing. CONCLUSION: The Fournier Device shows promise in the area of cytology and molecular diagnostics. The ability to perform cytology and molecular-based assays using a single sample obtained directly by the patient can lower the costs of screening and provide an efficient method of screening women in resource-poor countries or when cultural barriers exist to the use of traditional sampling methods.

Adult↗
PubMed1989

Microbiological profile of selected samples of "Al-Kohl" eye cosmetics in northern Jordanian provinces before and after use.

Fifty items of Al-Kohl collected from northern Jordanian provinces representing: 20 unopened ready to use samples purchased from retail outlets, 20 in-use samples obtained from ladies of different socioeconomic standards and 10 samples of the original stones (used for Al-Kohl preparation) were examined for their microbial contents. Ready to use and in-use samples were much more contaminated than the original stones. On sterility testing, more than 85% of the unused and in-use samples were contaminated with bacteria and or fungi comparing to 50% of the original stone samples. Quantitatively, 90% of the original stones contained less than 100 bacterial or fungal cells/g and the other remaining 10% were in the range of 10(2)-10(3) cfu/g either for bacterial or fungal counts. The level and distribution of the viable microbial counts in unused and in-use samples were comparable and much higher than original stones. More than 70% and 20% of those items contained more than 100 cfu/g of bacteria and fungi respectively. Among those samples 20% and 5% were heavily contaminated (contain more than 10(4) cfu/g) with bacteria and fungi respectively. Coliform bacteria in a number of 100 cfu/g or more were recovered from 10% of the unused and 20% of the in-use samples, none were recovered from original stones. The results of qualitative tests for identification of isolated microorganisms showed that 7 different species of Bacillus were found in the 50 examined samples. Approximately 50% of the examined samples contained Bacillus spp., Staphylococcus spp., Pseudomonas spp., P. vulgaris, S. marcescens were recovered from unused and in-use samples in different percentages, none from original stones, some of the detected Staphylococcus were aureus type and also one isolate of P. aeruginosa was detected in one of the in-use samples. The relationship between the detected level of microbial contamination in the tested samples with the proposed allowable international limits of contamination as well as the possible sources of contamination and the hygienic implications of using such products by the public were discussed.

Bacillus↗
PubMedDate not supplied

Monitoring of pesticide residues in human milk, soil, water, and food samples collected from Kafr El-Zayat Governorate.

Pesticide residues in human milk and environmental samples from Kafr El-Zayat Governorate in Egypt were analyzed. This governorate is located near one of the biggest pesticide factories in Egypt. Organochlorine and organophosphorus pesticides were monitored, including those that have been prohibited from use in Egypt. Human milk samples (31 samples) from Kafr El-Zayat were compared with 11 samples collected from Cairo. Data were compared with results from studies performed in 1987 and 1990. The present study showed that aldrin and dieldrin, heptachlor and heptachlor epoxide, and endrin residues have been eliminated from human milk. Estimated daily intakes (EDIs) of DDT complex and gamma-HCH by breast-fed infants in Kafr El-Zayat were 85.96 and 3.1% of the respective acceptable daily intakes (ADIs). beta-HCH residues showed an increasing pattern, especially in human milk samples from Cairo. DDT complex and HCH isomers in orange, spinach, lettuce, potatoes, and clover samples ranged from undetectable to very low concentrations. Higher levels of DDT and HCH were detected, but aldrin, dieldrin, endrin, and the heptachlors were not detected in food of animal origin. Residues in fish samples were below maximum residue limits established by some developed countries. Those in animal milk samples approached the extraneous residue limits of the Codex Committee on Pesticide Residues. HCH residues in soil were negligible, but DDT residues in soil were somewhat higher. Among water samples, groundwater samples had the highest residues of HCHs and DDTs, followed by Nile River water and then tap water. However, the organochlorine pesticide residues were found at concentrations below the maximum allowable limits set by the World Health Organization for drinking water. Among 12 organophosphorus pesticides monitored as parent compounds, dimethoate, malathion, methamidophos, and chlorpyrifos residues were detected in low concentrations in soil samples from a pesticide factory. No organophosphorus pesticide residues were found in plant samples, except for very low residues of dimethoate in an orange sample. Water samples were devoid of organophosphorus residues as parent compounds.

Animals↗
PubMed2002

Adaptive sampling in research on risk-related behaviors.

This article introduces adaptive sampling designs to substance use researchers. Adaptive sampling is particularly useful when the population of interest is rare, unevenly distributed, hidden, or hard to reach. Examples of such populations are injection drug users, individuals at high risk for HIV/AIDS, and young adolescents who are nicotine dependent. In conventional sampling, the sampling design is based entirely on a priori information, and is fixed before the study begins. By contrast, in adaptive sampling, the sampling design adapts based on observations made during the survey; for example, drug users may be asked to refer other drug users to the researcher. In the present article several adaptive sampling designs are discussed. Link-tracing designs such as snowball sampling, random walk methods, and network sampling are described, along with adaptive allocation and adaptive cluster sampling. It is stressed that special estimation procedures taking the sampling design into account are needed when adaptive sampling has been used. These procedures yield estimates that are considerably better than conventional estimates. For rare and clustered populations adaptive designs can give substantial gains in efficiency over conventional designs, and for hidden populations link-tracing and other adaptive procedures may provide the only practical way to obtain a sample large enough for the study objectives.

Adolescent↗
PubMed2003

Measurement uncertainty from physical sample preparation: estimation including systematic error.

A methodology is proposed, which employs duplicated primary sampling and subsequent duplicated physical preparation coupled with duplicated chemical analyses. Sample preparation duplicates should be prepared under conditions that represent normal variability in routine laboratory practice. The proposed methodology requires duplicated chemical analysis on a minimum of two of the sample preparation duplicates. Data produced from the hierarchical design is treated with robust analysis of variance (ANOVA) to generate uncertainty estimates, as standard uncertainties ('u' expressed as standard deviation), for primary sampling (ssamp), physical sample preparation (sprep) and chemical analysis (sanal). The ANOVA results allow the contribution of the sample preparation process to the overall uncertainty to be assessed. This methodology has been applied for the first time to a case study of pesticide residues in retail strawberry samples. Duplicated sample preparation was performed under ambient conditions on two consecutive days. Multi-residue analysis (quantification by GC-MS) was undertaken for a range of incurred pesticide residues including those suspected of being susceptible to loss during sample preparation procedures. Sampling and analytical uncertainties dominated at low analyte concentrations. The sample preparation process contributed up to 20% to the total variability and had a relative uncertainty (Uprep%) of up to 66% (for bupirimate at 95% confidence). Estimates of systematic errors during physical sample preparation were also made using spike recovery experiments. Four options for the estimation of measurement uncertainty are discussed, which both include and exclude systematic error arising from sample preparation and chemical analysis. A holistic approach to the combination and subsequent expression of uncertainty is advised.

Calibration↗
PubMed2000

Chorionic villus sampling before multifetal pregnancy reduction.

OBJECTIVE: This study was undertaken to determine the technical feasibility and accuracy of chorionic villus sampling before multifetal pregnancy reduction and to determine whether sampling increases the pregnancy loss rate after the reduction procedure. STUDY DESIGN: Between January 22, 1986, and January 20, 2000, a total of 1183 patients underwent first-trimester multifetal pregnancy reduction at Mount Sinai Medical Center. Chorionic villus sampling was attempted in 86 patients before the reduction procedure. Information on the technical success and accuracy of chorionic villus sampling, as well as pregnancy outcome, was collected on all patients. Pregnancy loss rates before 24 weeks' gestation in patients undergoing chorionic villus sampling before multifetal pregnancy reduction were compared with rates in patients not undergoing sampling. RESULTS: Chorionic villus sampling was successfully completed in 85 (98.8%) of 86 patients in whom sampling was attempted. Of 166 fetuses, 165 (99.4%) were successfully sampled. Of 165 fetuses, 3 (1.8%) had karyotypic abnormalities. Sampling errors were probably made in 2 (1.2%) of 165 fetuses. Of the 73 patients who have been delivered or are beyond 24 weeks' gestation, only 1 patient (1.4%) had a pregnancy loss after the multifetal pregnancy reduction. CONCLUSIONS: Chorionic villus sampling before multifetal pregnancy reduction is technically feasible and accurate, with an acceptably low sampling error rate. Chorionic villus sampling before multifetal pregnancy reduction appears to be safe and does not increase the risk of loss after the reduction procedure.

Adult↗
PubMed2001

Sampling description and procedures used to conduct the North/South Ireland Food Consumption Survey.

OBJECTIVE: The purpose of this survey was to establish a database of habitual food and drink consumption in a representative sample of Irish adults, aged 18-64 years. The present paper describes the sampling protocol, response rate and characteristics of the survey population in terms of sex and age groups, seasonality, geographical location, marital status, social class, socio-economic status and education level. DESIGN: A cross-sectional food consumption survey was carried out. In the Republic of Ireland, a nationally representative sample of adults was randomly selected with a validated two-stage clustered design, using the electoral register as the sampling frame. This method produced a self-weighting or 'epsem' sample of individuals, where each adult who was registered to vote had an equal opportunity of being selected. Similarly, in Northern Ireland, a two-stage random sampling procedure was used. The sampling frame was the electoral register, and the sample was stratified by urban/rural and by an index of material deprivation, to ensure representation of each sector of the community. The recruitment procedure was the same in the North and South. An introductory letter with an information leaflet was posted to each selected individual and these were followed up by a visit from a fieldworker, who invited participation in the survey. SETTING: Northern Ireland and Republic of Ireland between 1997 and 1999. RESULTS: The response rate, which is the percentage of the total number of people who completed a 7-day food diary (n=1379) out of the total eligible sample (n=2177), was 63%. Non-respondents and dropouts constituted 34% and 3%, respectively, of the total eligible sample. Compared with the most recent census figures available, the sample was generally found to be representative in terms of sex and age group profiles, geographical location, marital status, seasonality, social class, socio-economic group and education level. Data on sex and age group and geographical location were collected from non-respondents for comparison with the survey sample. There were no apparent differences between them. CONCLUSION: The North/South Ireland Food Consumption Survey has established a relational database of habitual food and drink consumption, in addition to data on habitual physical activity, anthropometric measurements, socio-demographic factors, lifestyle, health status indicators and attitudes, in a nationally representative sample of the population of the island of Ireland.

Adolescent↗
PubMed2005

A general equation for estimating glomerular filtration rate from a single plasma sample.

OBJECTIVES: Glomerular filtration rate (GFR) may be estimated from a single plasma sample measurement using empirical equations. This method forms the basis of international guidelines on GFR measurement. New guidelines have recently been recommended by the British Nuclear Medicine Society (BNMS). These use the slope-intercept technique in which several samples are obtained. Quality control of measurement may be achieved by comparison with the individual single-sample values. This paper compares international guideline single-sample estimates of GFR with the new BNMS method and derives an improved general single-sample equation. METHODS: GFR measurements using Tc-DTPA were performed on 180 adults and 100 children using samples at approximately 2 h and 3 h and a further 45 adults with samples at 2, 3 and 4 h. The two-sample values obtained using the BNMS guideline method were compared to one-sample estimates obtained using (1) international guidelines and (2) a new equation derived from the data. The new equation was evaluated in a further 145 subjects. RESULTS: The international guidelines technique had systematic differences between the one-sample and two-sample estimates of GFR. The new equation had minimal systematic error and reduced random error (standard error of the estimate 4.5 ml . min per 1.73 m). CONCLUSIONS: There were significant differences between GFR values obtained using the international guidelines single-sample method and the slope-intercept method described in the BNMS guidelines. The new equation described in this paper gave considerably improved agreement and is recommended if single-sample estimates are to be used as quality control for BNMS guideline measurements.

Adult↗
PubMed1996

Sampling homosexuals, bisexuals, gays, and lesbians for public health research: a review of the literature from 1990 to 1992.

Our objective was to examine the representativeness of samples of homosexuals, bisexuals, gays, and lesbians obtained for public health research. We identified journal articles cited in Medline and published between 1990 and 1992 that sampled individuals and classified them as homosexual, bisexual, gay, and/or lesbian. Information was abstracted from these articles to evaluate four components of sample selection affecting the representativeness of samples: (1) how the population is conceptually defined, (2) how the sampled population is operationally identified, (3) the setting from which samples are selected, and (4) the use of probability sampling to select subjects. We identified 152 public health articles published between 1990 and 1992 that sampled homosexuals, bisexuals, gays, and/or lesbians. We found articles (1) rarely (4/152) conceptually defined the population they were sampling, (2) used a range of incomparable methods to identify and select subjects, (3) sampled from settings representative of dramatically different populations, and (4) rarely (3/152) used probability sampling. Overall, we find methods used to identify homosexuals, bisexuals, gays, and lesbians for public health research produce samples representative of different and sometimes unidentifiable populations. To understand these populations from a public health perspective, it is imperative that steps be taken by researchers to standardize population definitions and sampling methodologies.

Bisexuality↗
PubMed1994

The consistency of estimates obtained through central-location sampling: analysis of the Partnership for a Drug-Free America Attitude Tracking Study.

To evaluate the reliability and validity of estimates of drug use obtained through multiple-site central-location sampling, data from the Partnership Attitude Tracking Study (PATS), collected annually beginning in 1987, are tracked longitudinally and compared with data collected through traditional household interviews. Comparisons with demographic estimates from Current Population Surveys indicate that central-location sampling can provide a broadly representative sample of the adult population. However, there is some coverage bias in central-location sampling, most notably in the underrepresentation of adults who do not have high school diplomas. Sample estimates obtained from central-location sampling are consistent over time. Basic demographic characteristics of the samples--education, income, marital status, and area of residence--vary by less than 5% across the four waves of the tracking study. Prevalence estimates of self-reported drug use demonstrate an even higher degree of consistency over time. Comparisons of PATS and National Household Survey of Drug Abuse data and the Monitoring the Future data indicate a higher level of drug use and a lower level of perceived risk of occasional use among PATS respondents. While the trends in use and perceived risk reported in all studies are similar, we suggest that perceived threats to confidentiality and anonymity often result in significant underreporting of drug use, particularly in household surveys. Sample estimate differences are attributed to sampling and measurement error. Some discrepancy in prevalence estimates is associated with the fact that the PATS sample is not a true probability sample; as a result, the sampling error of the overall study cannot be estimated precisely. It is also likely that the difference in estimates between the studies is a product of the decreased measurement error of PATS methodology. In central-location sampling, respondents are completely anonymous and may feel more comfortable in providing honest answers about illicit activities such as drug use. The potential applications of this methodology are discussed.

Adolescent↗