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1.
In response to Abbott and Volberg's (in press) rejoinder to my epidemiologic note on verification bias and estimation of prevalence rates (Gambino, in press), I provide the formulas for computing confidence intervals for the results of second-stage verification. In addition, I provide the appropriate equation for determining confidence intervals when prevalence is near zero or one. Finally, we present formulas for determining the most efficient sample sizes needed to minimize second-stage variance estimates. These allow the investigator working under a fixed budget to determine the relative value of sampling negative screens to test for false negatives. We close with an observation on the interpretability of evidence.  相似文献   

2.
While two-stage designs in problem gambling research are expensive and relatively difficult to execute, they have the potential to yield more accurate prevalence estimates as well as valuable additional information about gambling and problem gambling in the community. However, gains in precision are heavily dependent on the accuracy of the screening methods used and the sample sizes involved. Sound practice requires reliable information about the variances and confidence levels associated with different screens. In the spirit of contributing to the ongoing dialog about ways to improve the measurement of problem gambling, we examine several reasons to question whether the revised estimates offered by Gambino are in fact an improvement.  相似文献   

3.
We study Danish adult gambling behavior with an emphasis on discovering patterns relevant to public health forecasting and economic welfare assessment of policy. Methodological innovations include measurement of formative in addition to reflective constructs, estimation of prospective risk for developing gambling disorder rather than risk of being falsely negatively diagnosed, analysis with attention to sample weights and correction for sample selection bias, estimation of the impact of trigger questions on prevalence estimates and sample characteristics, and distinguishing between total and marginal effects of risk-indicating factors. The most significant novelty in our design is that nobody was excluded on the basis of their response to a ‘trigger’ or ‘gateway’ question about previous gambling history. Our sample consists of 8405 adult Danes. We administered the Focal Adult Gambling Screen to all subjects and estimate prospective risk for disordered gambling. We find that 87.6% of the population is indicated for no detectable risk, 5.4% is indicated for early risk, 1.7% is indicated for intermediate risk, 2.6% is indicated for advanced risk, and 2.6% is indicated for disordered gambling. Correcting for sample weights and controlling for sample selection has a significant effect on prevalence rates. Although these estimates of the ‘at risk’ fraction of the population are significantly higher than conventionally reported, we infer a significant decrease in overall prevalence rates of detectable risk with these corrections, since gambling behavior is positively correlated with the decision to participate in gambling surveys. We also find that imposing a threshold gambling history leads to underestimation of the prevalence of gambling problems.  相似文献   

4.
The focus of this report is to examine the process of validation of new screening tests designed to detect the problem gambler in research and practice settings. A hierarchical or phases of evaluation model is presented as a conceptual framework to describe the basic features of the validation process and its implications for application and interpretation of test results. The report describes a number of threats to validity in the form of sources of unintended bias that when unrecognized may lead to incorrect interpretations of study results and the drawing of incorrect conclusions about the usefulness of the new screening tests. Examples drawn from the gambling literature on problem gambling are used to illustrate some of the more important concepts including spectrum bias and clinical variation in test accuracy. The concept of zones of severity and the bias inherent in selecting criterion thresholds are reviewed. A definition of reference or study gold standard is provided. The use of 2-stage designs to establish validity by efficiently using reference standards to determine indices of accuracy and prevalence is recommended.  相似文献   

5.
Much of the debate over how best to estimate the prevalence of problem gambling in the general population is driven by a number of misconceptions, misinterpretations, and questionable, sometimes erroneous assumptions. Among the latter is the failure to understand that what is being validated is not the test but the interpretation of test scores for a specific purpose. In addition there has been a lack of attention to defining the clinical and/or epidemiologic relevance of case definitions in terms of severity and other clinical attributes, a misunderstanding of how test values are interpreted when criterion thresholds or cut-off points are selected, and a failure to replicate the validation of criterion thresholds for defining cases of problem gambling. It is argued further that the distinction between dichotomy and continuum is a false choice, and any emphasis on overestimation is misdirected. Alternative methods for evaluating tests and estimating prevalence are described and a pragmatic empirical approach to the interpretation of prevalence estimates is recommended.  相似文献   

6.
This study uses social network analysis to model a contact network of people who inject drugs (PWID) relevant for investigating the spread of an infectious disease (hepatitis C). Using snowball sample data, parameters for an exponential random graph model (ERGM) including social circuit dependence and four attributes (location, age, injecting frequency, gender) are estimated using a conditional estimation approach that respects the structure of snowball sample designs. Those network parameter estimates are then used to create a novel, model-dependent estimate of network size. Simulated PWID contact networks are created and compared with Bernoulli graphs. Location, age and injecting frequency are shown to be statistically significant attribute parameters in the ERGM. Simulated ERGM networks are shown to fit the collected data very well across a number of metrics. In comparison with Bernoulli graphs, simulated networks are shown to have longer paths and more clustering. Results from this study make possible simulation of realistic networks for investigating treatment and intervention strategies for reducing hepatitis C prevalence.  相似文献   

7.
Regression coefficients specify the partial effect of a regressor on the dependent variable. Sometimes the bivariate or limited multivariate relationship of that regressor variable with the dependent variable is known from population‐level data. We show here that such population‐level data can be used to reduce variance and bias about estimates of those regression coefficients from sample survey data. The method of constrained MLE is used to achieve these improvements. Its statistical properties are first described. The method constrains the weighted sum of all the covariate‐specific associations (partial effects) of the regressors on the dependent variable to equal the overall association of one or more regressors, where the latter is known exactly from the population data. We refer to those regressors whose bivariate or limited multivariate relationships with the dependent variable are constrained by population data as being "directly constrained." Our study investigates the improvements in the estimation of directly constrained variables as well as the improvements in the estimation of other regressor variables that may be correlated with the directly constrained variables, and thus "indirectly constrained" by the population data. The example application is to the marital fertility of black versus white women. The difference between white and black women's rates of marital fertility, available from population‐level data, gives the overall association of race with fertility. We show that the constrained MLE technique both provides a far more powerful statistical test of the partial effect of being black and purges the test of a bias that would otherwise distort the estimated magnitude of this effect. We find only trivial reductions, however, in the standard errors of the parameters for indirectly constrained regressors.  相似文献   

8.
Gambling participation and rates of problem gambling change over time in response to a variety of factors including gambling availability, demographic changes and adaptation at individual and societal levels. These relationship are complex and only partially understood. The major aim of the present study was to provide general population estimates of gambling participation and problem gambling for Sweden and compare these estimates with estimates from a previous national study. The study was also designed to identify risk factors for problem gambling including change in these factors over time. Data are from the first phase of the Swedish Longitudinal Gambling Study (Swelogs) in which a representative sample of 8,165 people was assessed using validated problem gambling and other measures to facilitate comparison with findings from the 1997/1998 Swedish Gambling Study (Swegs). Overall, it was found that gambling participation reduced markedly, although in some population sectors increases were evident for some forms including poker and electronic gaming machines. Lifetime prevalence of probable pathological gambling increased; however, past 12 months probable pathological and problem gambling prevalence did not. Males, younger adults and people born outside Sweden were at high risk in both studies. Significant prevalence increases were evident for people aged 18–24 and those with low levels of education. The results indicate that relationships between gambling exposure, participation and problems are dynamic with shifting implications for public health and social policy.  相似文献   

9.
I examine evidence on private sector union wage gaps in the United States. The consensus opinion among labor economists of an average union premium of roughly 15 percent is called into question. Two forms of measurement error bias downward standard wage gap estimates. Match bias results from Census earnings imputation procedures that do not include union status as a match criterion. Downward bias is roughly equal to the proportion of workers with imputed earnings, currently about 30 percent. Misclassification of union status causes additional attenuation in union gap measures. This bias has worsened as private sector density has declined, since an increasing proportion of workers designated as union are instead nonunion workers. Corrections for misclassification and match bias lead to estimated union gaps substantially higher than standard estimates, but with less of a downward trend since the mid 1980s. Private sector union gaps corrected for these biases are estimated from the CPS for 1973–2001. The uncorrected estimate for 2001 is .13 log points. Correction for match bias increases the gap to .18 log points; further correction for misclassification bias, based on an assumed 2 percent error rate, increases the gap to .24. Reexamination of the skill-upgrading hypothesis leads to the conclusion that higher union gap estimates are plausible. The conventional wisdom of a 15 percent union wage premium warrants reexamination.  相似文献   

10.
The concern that the South Oaks Gambling Screen (SOGS) and other screening tests have a relatively high rate of false positive errors which results in overestimation of the true prevalence in general population studies is shown to be unfounded. False positives are seen to be a necessary but not sufficient condition for overestimation. It is demonstrated that the proper research question is whether the sample prevalence estimator is biased, and, if so, in which direction. One solution to the problem of bias is shown to depend on the availability of estimates of the error rates of the test.  相似文献   

11.
Mean scaling is a common assumption in the estimation of aggregate consumer elasticities—in particular, expenditure elasticities, but also (implicitly) compensated price elasticities. The assumption is that each household’s income changes in the same proportion as aggregate income. If correct, that implies no bias in the use of aggregate data for estimation of expenditure elasticities. If incorrect, though, there may be substantial bias, especially if there is a high degree of inequality in the underlying income distribution, and regardless of whether one uses micro or aggregate data. We explore this issue, both theoretically and illustratively, using realistic (empirically derived) elasticity estimates coupled with relatively high and low degrees of income inequality.  相似文献   

12.
This paper reports the results of a series of experiments conducted to measure the effects of alternative procedures for determining the size of social networks. The three methods tested are recall, recognition, and numerical estimation. Respondents were selected from work, church, and social groups. The major findings were that recall estimates are substantially below those obtained by recognition methods and become worse for larger groups. On average, numerical estimates are reasonable approximations of network size estimates based on recognition, but there is substantial variability in the accuracy of individual reports. Surprisingly, there is no evidence that recall is better for reports on number of close friends than of friends or acquaintances. There are order effects on numerical estimates of network size and better estimates are obtained by first asking about close friends. Finally, there is some evidence that respondent characteristics such as age affect recall of network size.  相似文献   

13.
The prevalence of male same‐gender sexual behavior in Mexico City in relation to HIV transmission was studied. A household probability survey of 8,068 adult men was conducted in 1992–93 using the Mexican National Health Survey sampling frame. The response rate was 59%. Differences between respondents and nonrespondents indicated no evidence for significant bias. A random subsample of 1,116 individuals provided serum or saliva for HIV testing. An estimated 2.5% of men practiced same‐gender sex in their lifetime: 2.1% (95% CI: 1.7 ‐ 2.4%) reported bisexual behavior and 0.4% (95% CI: 0.3 ‐ 0.6%) reported exclusively homosexual behavior. Among bisexuals, 70% reported sex only with women in the previous year, 7% reported sex only with men, 13% reported sex with both, and 10% were sexually inactive. A condom was used by 46% in their last homosexual encounter. An estimated 0.1% of married men were homosexually active in the previous year. The HTV prevalence estimate was 0.2% in the sample. The rate was 4% among homosexual/bisexual men and 0.09% in heterosexual men (p < 0.0001). Estimates of homosexual behavior and HTV infection from this population‐based sample are lower than results from nonprobability studies. The low prevalence of condom use anticipates future growth of the epidemic in the homosexual population. Bisexual behavior appeared to be infrequent and transitory, particularly among married men.  相似文献   

14.
Nonresponse Rates and Nonresponse Bias in Household Surveys   总被引:11,自引:1,他引:10  
Many surveys of the U.S. household population are experiencinghigher refusal rates. Nonresponse can, but need not, inducenonresponse bias in survey estimates. Recent empirical findingsillustrate cases when the linkage between nonresponse ratesand nonresponse biases is absent. Despite this, professionalstandards continue to urge high response rates. Statisticalexpressions of nonresponse bias can be translated into causalmodels to guide hypotheses about when nonresponse causes bias.Alternative designs to measure nonresponse bias exist, providingdifferent but incomplete information about the nature of thebias. A synthesis of research studies estimating nonresponsebias shows the bias often present. A logical question at thismoment in history is what advantage probability sample surveyshave if they suffer from high nonresponse rates. Since postsurveyadjustment for nonresponse requires auxiliary variables, theanswer depends on the nature of the design and the quality ofthe auxiliary variables.  相似文献   

15.
《Social Networks》1987,9(4):333-349
Selectivity bias is a danger whenever observations are systematically excluded from a data set on the basis of a dependent variable, whether this exclusion is explicit or implicit. If present, the problem has severe consequences for the validity of statistical estimates of effects. The problem is of importance to the analysis of survey network data, since many network measures (such as density) are available only for persons having networks of size two or larger, while others (such as percent kin) are defined only for those having networks of size one or more. Analysts can adjust for selectivity bias by estimating the risk of exclusion (in this case, of having a network of size 0 or 1), and including the modeled risk as a control in substantive equations. Such estimates are presented for the 1985 General Social Survey network data; in the course of this results of Fischer and Phillips on social isolation are replicated. Other ways of guarding against selection bias are also discussed; at a minimum, network size should be included among the set of regressors in analyses of survey network data, as a methodological control if not as a substantive variable.  相似文献   

16.
This paper, which is the first large-scale application of respondent-driven sampling (RDS) to nonhidden populations, tests three factors related to RDS estimation against institutional data using two WebRDS samples of university undergraduates. First, two methods of calculating RDS point estimates are compared. RDS estimates calculated using both methods coincide closely, but variance estimation, especially for small groups, is problematic for both methods. In one method, the bootstrap algorithm used to generate confidence intervals is found to underestimate variance. In the other method, where analytical variance estimation is possible, confidence intervals tend to overestimate variance. Second, RDS estimates are found to be robust against varying measures of individual degree. Results suggest the standard degree measure currently employed in most RDS studies is among the best-performing degree measures. Finally, RDS is found to be robust against the inclusion of out-of-equilibrium data. The results show that valid point estimates can be generated with RDS analysis using real data, but that further research is needed to improve variance estimation techniques.  相似文献   

17.
This study examines the impact of passive and active parental consent procedures on the type of adolescents participating in a school-based survey examining substance use. Schools recruited from a random sample of metropolitan schools were assigned to passive or active parental consent condition. Results showed that participation rates in active consent schools were lower than in passive consent schools for junior students (60% vs. 80%) but not senior students. Although consent condition had limited impact on prevalence estimates among older students, among younger students estimates of cannabis use and ecstasy use were higher in the passive consent condition than the active consent condition. Active consent procedures introduce some degree of selection bias into studies of adolescents' substance use and may compromise the external validity of prevalence estimates produced, especially among younger students.  相似文献   

18.
Age‐period‐cohort (APC) accounting models have long been objects of attention in statistical studies of human populations. It is well known that the identification problem created by the linear dependency of age, period, and cohort (Period = Age + Cohort or P = A + C) presents a major methodological challenge to APC analysis, a problem that has been widely addressed in demography, epidemiology, and statistics. This paper compares parameter estimates and model fit statistics produced by two solutions to the identification problem in age‐period‐cohort models—namely, the conventional demographic approach of constrained generalized linear models (Fienberg and Mason 1978, 1985; Mason and Smith 1985) and the intrinsic estimator method recently developed by Fu (2000; Knight and Fu 2000; Fu, Hall, and Rohan 2004). We report empirical analyses of applications of these two methods to population data on U.S. female mortality rates. Comparisons of parameter estimates suggest that both constrained generalized linear models and the intrinsic estimator method can yield similar estimates of age, period, and cohort effects, but estimates obtained by the intrinsic estimator are more direct and do not require prior information to select appropriate model identifying constraints. We also describe three statistical properties of the estimators: (1) finite‐time‐period bias, (2) relative statistical efficiency, and (3) consistency as the number of periods of observed data increases. These empirical analyses and theoretical results suggest that the intrinsic estimator may well provide a useful alternative to conventional methods for the APC analysis of demographic rates .  相似文献   

19.
Nonresponse Bias in a Dual Frame Sample of Cell and Landline Numbers   总被引:4,自引:4,他引:0  
We conducted a dual frame survey of landline and cell phonenumbers in 2004 to evaluate the feasibility of including cellphone numbers in random digit dial telephone surveys in theUnited States. By sampling cell phone numbers, the coveragebias associated with households that have only cell phones iseliminated. However, we discovered two major sources of nonresponsebias in the dual frame sample. In an attempt to reduce thesebiases, we applied several different estimation schemes. Buta comparison to the 2004 Current Population Survey Cell PhoneSupplement showed that none of the estimation schemes substantiallyreduced the nonresponse bias of the estimates. We suggest othermethods that might be used in future surveys that include cellphones and discuss the need for additional data collection andresearch on this issue.  相似文献   

20.
Among young adults who use condoms, incomplete condom use (putting a condom on after beginning or taking a condom off before finishing sex) and condom failure (condom breaking or slipping off during sex) are common. Therefore, sexual behavior surveys that ask only if a condom was used are likely to underestimate the actual prevalence of unprotected sex. This study examined data from 135 sexually active perinatally HIV-infected (PHIV+) youth and perinatally exposed but uninfected (PHIV?) youth, ages 13 to 24. Participants were asked whether they used a condom on their first and their most recent occasion of vaginal sex. Youth who reported using a condom were asked a follow-up question about whether there was any time during that occasion when sex was not protected by a condom. This follow-up question identified additional participants— almost double the proportions who initially said they did not use a condom—who had unprotected sex. Incomplete condom use was similar among PHIV+ and PHIV?youth, boys and girls, Latinos and African Americans, and younger and older youth. These findings illustrate the importance of asking specifically about whether any unprotected behavior occurred from start to finish of sex to achieve more valid estimates of sexual risk behavior.  相似文献   

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