The abcissa on certain figures in "Statistical Modeling and Analysis of Trace Element Concentrati... more The abcissa on certain figures in "Statistical Modeling and Analysis of Trace Element Concentrations in Forensic Glass Evidence" [Pan and Kafadar (2018)] and the corresponding supplement have been corrected. Estimated match rates are around 20-30% lower than originally stated (when the true relative difference in concentrations is less than 15% in all elements); however, the main results and conclusions of the paper remain unchanged. Two samples that come from batches whose mean log concentrations differ by δ = 0.1 (roughly 10%) in all 17 elements would not be "considered distinguishable" [ASTM International (2016), Section 11.1.7] 62.22-65.41% of the time using the covariance matrix estimate from the German data, and 77.18-78.14% of the time using the estimate from the Canadian data set. Affected figures and tables below are labeled corresponding to Pan and Kafadar (2018). Section 2 contains corrected supplemental figures and tables.
Fundamental concepts in statistics form the cornerstone of scientific inquiry. If we fail to unde... more Fundamental concepts in statistics form the cornerstone of scientific inquiry. If we fail to understand fully these fundamental concepts, then the scientific conclusions we reach are more likely to be wrong. This is more than supposition: for 60 years, statisticians have warned that the scientific literature harbors misunderstandings about basic statistical concepts. Original articles published in 1996 by the American Physiological Society’s journals fared no better in their handling of basic statistical concepts. In this review, we summarize the two main scientific uses of statistics: hypothesis testing and estimation. Most scientists use statistics solely for hypothesis testing; often, however, estimation is more useful. We also illustrate the concepts of variability and uncertainty, and we demonstrate the essential distinction between statistical significance and scientific importance. An understanding of concepts such as variability, uncertainty, and significance is necessary, b...
Evidence Based Library and Information Practice, 2008
Objective – This article measures the extent of the synonym problem in full-text searching. The s... more Objective – This article measures the extent of the synonym problem in full-text searching. The synonym problem occurs when a search misses documents because the search was based on a synonym and not on a more familiar term. Methods – We considered a sample of 90 single word synonym pairs and searched for each word in the pair, both singly and jointly, in the Yahoo! database. We determined the number of web sites that were missed when only one but not the other term was included in the search field. Results – Depending upon how common the usage is of the synonym, the percentage of missed web sites can vary from almost 0% to almost 100%. When the search uses a very uncommon synonym ("diaconate"), a very high percentage of web pages can be missed (95%), versus the search using the more common term (only 9% are missed when searching web pages for the term "deacons"). If both terms in a word pair were nearly equal in usage ("cooks" and "chefs"), t...
Length-biased sampling exists in screening programs where longer duration disease is detected dur... more Length-biased sampling exists in screening programs where longer duration disease is detected during the preclinical stage because a longer sojourn time (preclinical duration) has a higher probability of being screen detected. By modeling the course of disease, we quantify the effect of length-biased sampling on clinical duration when cases are subject to periodic screening with variable test sensitivity. We use the highly flexible bivariate lognormal density to jointly model preclinical and clinical durations, and we model screening test sensitivity as a function of the sojourn time and number of previous false negative screens. We show that the mean clinical duration among screen-detected cases can be up to 40% higher, with shrinking standard deviation, than those among nonscreen-detected cases, due to biased sampling alone, irrespective of any possible benefit (increased survival time arising from earlier detection or reduction in mortality). These findings will aid in the design and interpretation of screening trials.
ABSTRACT We develop a probability model for evaluating long-term effects due to regular screening... more ABSTRACT We develop a probability model for evaluating long-term effects due to regular screening. People who take part in cancer screening are divided into four mutually exclusive groups: True-early-detection, No-early-detection, Overdiagnosis, and Symptom-free-life. For each case, we derive the probability formula. Simulation studies using the HIP (Health Insurance Plan for Greater New York) breast cancer study data provide estimates for these probabilities and the corresponding credible intervals. These probabilities change with a person’s age at study entry, screening frequency, screening sensitivity, and other parameters. We also allow the human life time to be subject to a competing risk of death from other causes. The model can provide policy makers with important information regarding the distribution of individuals participating in a screening program who eventually fall into one of the four groups.
Proceedings of the Royal Society B: Biological Sciences, 2014
Developmental responses to nutritional variation represent one of the ecologically most important... more Developmental responses to nutritional variation represent one of the ecologically most important classes of adaptive plasticity. However, knowledge of genome-wide patterns of nutrition-responsive gene expression is limited. Here, we studied genome-wide transcriptional responses to nutritional variation and their dependency on trait and sex in the beetle Onthophagus taurus. We find that averaged across the transcriptome, nutrition contributes less to overall variation in gene expression than do sex or body region, but that for a modest subset of genes nutrition is by far the most important determinant of expression variation. Furthermore, our results reject the hypothesis that a common machinery may underlie nutrition-sensitive development across body regions. Instead, we find that magnitude (measured by number of differentially expressed contigs), composition (measured by functional enrichment) and evolutionary consequences (measured by patterns of sequence variation) are heavily d...
This paper presents and develops three approaches for evaluating the degree of "homogeneity" or "... more This paper presents and develops three approaches for evaluating the degree of "homogeneity" or "randomness" present in a two-dimensional material. Such problems of detecting homogeneity arise in several technological, biological and geological applications. The first approach defines the concept of a "cluster" and develops some test statistics based on the number of clusters and their size distribution. The second approach divides the material into blocks and then applies a nonparametric analysis of variance to these blocks. The third approach employs a graph-theoretic model, in which the length of a certain minimum spanning tree is used as a measure of homogeneity. These approaches are compared using simulation experiments, and are then applied to a problem from materials science.
Frequently, a sample may contain observations that differ substantially from the other data value... more Frequently, a sample may contain observations that differ substantially from the other data values. There are various ways to deal with the possibility of such values so that the resulting analysis will not be adversely affected if they are present. All of these methods assign weights to observations according to some well-conceived algorithm. In this article we concentrate on two forms of assigning weights to observations. The first is trimming, which corresponds to assigning zero weight to a prespecified fraction of the extreme observations and equal weights to the rest. The second is Winsorizing, which also assign zero weights to the extreme observations, as in trimming, but assigns extra weight to the most extreme observations in the retained sample. In this article we will define these concepts for a single sample of observations, and briefly discuss the applications to more complex problems like regression.
Editor's Note: This article is one of two that will be presented orally at the Technometrics... more Editor's Note: This article is one of two that will be presented orally at the Technometrics session of the 38th Annual Fall Technical Conference, to be held in Birmingham, Alabama, October 20-21, 1994. The conference is cosponsored ...
Screening for a disease such as cancer is often regarded as a beneficial and successful strategy ... more Screening for a disease such as cancer is often regarded as a beneficial and successful strategy for reducing mortality. However, as with any clinical treatment or intervention, benefit cannot be assumed, and screening can entail both costs and harms, so the screening as a ‘treatment’ must undergo evaluation. An evaluation requires a definition of the treatment ‘benefit’, design of studies to measure that benefit with as little bias and variance as possible, and the development of methods for estimating the potential benefit. In screening studies, the factors most central to the evaluation are unobservable (e.g. earliest point in time at which disease becomes detectable, or ‘preclinical’; time at which disease might have been detected in the absence of screening; test sensitivity). Thus, screening programs should be evaluated on scenarios in which these factors are varied, to ensure the robustness of the estimated benefit under a variety of circumstances. This article describes the ...
Screening tests are used frequently for control of diseases such as cancer. The increased surviva... more Screening tests are used frequently for control of diseases such as cancer. The increased survival time of screen‐detected cases over those that are detected clinically may be due in part to ‘lead time’, or the length of time by which the disease is diagnosed earlier by screening in the presence or absence of any real extension in survival time. A realistic evaluation of screening needs to assess the true benefit of screening; that is, the length of time by which survival has been extended, beyond merely the time of the advanced diagnosis. The comparison of survival measured from time of entry between cases in a screening arm and in a control arm in randomized studies avoids the lead time bias. If the effects of average lead time and average benefit on survival are additive, these effects can be estimated by recognizing that (a) the difference in survival curves since time of diagnosis confounds benefit and lead time, but (b) the difference in survival curves since time of start of ...
Randomized screening trials provide the optimal means of assessing the benefit of screening for c... more Randomized screening trials provide the optimal means of assessing the benefit of screening for cancer and other chronic diseases. Unlike therapy trials, however, where strict eligibility criteria assure the comparability of cases of disease in the arms of the trial, the cancer cases identified during follow‐up are a subset of all randomized participants. Furthermore, those cases detected by screening tend to arise from length biased sampling which also can bias estimates of the screening benefit and of average lead time. To reduce or eliminate this bias, we propose several methods for defining comparable groups of cases from the trial arms. We examine, via simulation, these methods with respect to their effects on (i) point and interval estimates of average lead time and average benefit time and (ii) the logrank test statistic for a mortality effect of screening. The most successful new method for defining comparable case groups uses an estimate of the mean sojourn time (mean precl...
Detecting patterns in health-related data for geographic areas is facilitated with the use of exp... more Detecting patterns in health-related data for geographic areas is facilitated with the use of exploratory methods, especially smoothing. In addition, these data often must be adjusted for known prognostic factors such as age and gender. The analysis in this paper focuses on mortality rates due to malignant melanoma in White males and White females; these data are adjusted for both age and latitude, separately for males and females, and then smoothed using (a) a non-linear smoother known as weighted head-banging, and (b) a new method that incorporates the adjustment and the smoothing simultaneously. Maps of the continental United States show regions of high rates, even after having adjusted for age and latitude, and suggest the possibility of other variables that may influence the rates.
John Tukey's impact on statistics, and on science in general, is broad and lasting. This article ... more John Tukey's impact on statistics, and on science in general, is broad and lasting. This article discusses some of these contributions, with a special emphasis on those that led to the development of robust methods and data exploration. In view of today's emphasis on data mining techniques, the recollection of Tukey's influence is especially timely.
Large-scale strategies are needed to reduce overuse of antibiotics in US communities. To evaluate... more Large-scale strategies are needed to reduce overuse of antibiotics in US communities. To evaluate the impact of a mass media campaign-"Get Smart Colorado"-on public exposure to campaign, antibiotic use, and office visit rates. Nonrandomized controlled trial. Two metropolitan communities in Colorado, United States. The general public, managed care enrollees, and physicians residing in the mass media (2.2 million persons) and comparison (0.53 million persons) communities. : The campaign consisting of paid outdoor advertising, earned media and physician advocacy ran between November 2002 and February 2003. Antibiotics dispensed per 1000 persons or managed care enrollees, and the proportion of office visits receiving antibiotics measured during 10 to 12 months before and after the campaign. After the mass media campaign, there was a 3.8% net decrease in retail pharmacy antibiotic dispenses per 1000 persons (P = 0.30) and an 8.8% net decrease in managed care-associated antibiotic dispenses per 1000 members (P = 0.03) in the mass media community. Most of the decline occurred among pediatric members, and corresponded with a decline in pediatric office visit rates. There was no change in the office visit prescription rates among pediatric or adult managed care members, nor in visit rates for complications of acute respiratory tract infections. A low-cost mass media campaign was associated with a reduction in antibiotic use in the community, and seems to be mediated through decreases in office visits rates among children. The campaign seems to be cost-saving.
Journal of the American Statistical Association, 1982
Kafadar: A Biweight Approach to the One-Sampie Problem 417 in Lax (1975, as referenced in Mostell... more Kafadar: A Biweight Approach to the One-Sampie Problem 417 in Lax (1975, as referenced in Mosteller and Tukey 1977, p. 207). In terms of their average values, ave(iw) and ave(i<0)) approach cr and (2/3)cr, respectively, as n ...
Earlier work by Saha et al. rigorously derived a general probabilistic model for the PCR process ... more Earlier work by Saha et al. rigorously derived a general probabilistic model for the PCR process that includes as a special case the Velikanov-Kapral model where all nucleotide reaction rates are the same. In this model the probability of binding of deoxy-nucleoside triphosphate (dNTP) molecules with template strands is derived from the microscopic chemical kinetics. A recursive solution for the probability function of binding of dNTPs is developed for a single cycle and is used to calculate expected yield for a multicycle PCR. The model is able to reproduce important features of the PCR amplification process quantitatively. With a set of favorable reaction conditions, the amplification of the target sequence is fast enough to rapidly outnumber all side products. Furthermore, the final yield of the target sequence in a multicycle PCR run always approaches an asymptotic limit that is less than one. The amplification process itself is highly sensitive to initial concentrations and the reaction rates of addition to the template strand of each type of dNTP in the solution. This paper extends the earlier Saha model with a physics based model of the dependence of the reaction rates on temperature, and estimates parameters in this new model by nonlinear regression. The calibrated model is validated using RT-PCR data.
Background. The effect of urbanization on age-adjusted lung cancer mortality rates in US counties... more Background. The effect of urbanization on age-adjusted lung cancer mortality rates in US counties is investigated. The data come from National Cancer Institute, and urban trends are estimated in time periods 1970-1979 and 1980-1987, for both white males and white females. To account for possibly different gradients in different parts of the country, the 48 contiguous states are divided into seven regions. Methods. A measure of urbanness, urbanicity, is defined and is used to stratify counties. A multiplicative model is proposed that relates county mortality rates to urbanicity. The residuals from this multiplicative model serve as age-and urbanadjusted rates. Results. Urban-rural gradients are significant for nearly all regions for both white males and white females, diminishing slightly in the latter time period for white males but becoming stronger for white females. Conclusions. The age-and urban-adjusted rates may be used in mapping to investigate geographical patterns that remain after removal of the urban factor.
The abcissa on certain figures in "Statistical Modeling and Analysis of Trace Element Concentrati... more The abcissa on certain figures in "Statistical Modeling and Analysis of Trace Element Concentrations in Forensic Glass Evidence" [Pan and Kafadar (2018)] and the corresponding supplement have been corrected. Estimated match rates are around 20-30% lower than originally stated (when the true relative difference in concentrations is less than 15% in all elements); however, the main results and conclusions of the paper remain unchanged. Two samples that come from batches whose mean log concentrations differ by δ = 0.1 (roughly 10%) in all 17 elements would not be "considered distinguishable" [ASTM International (2016), Section 11.1.7] 62.22-65.41% of the time using the covariance matrix estimate from the German data, and 77.18-78.14% of the time using the estimate from the Canadian data set. Affected figures and tables below are labeled corresponding to Pan and Kafadar (2018). Section 2 contains corrected supplemental figures and tables.
Fundamental concepts in statistics form the cornerstone of scientific inquiry. If we fail to unde... more Fundamental concepts in statistics form the cornerstone of scientific inquiry. If we fail to understand fully these fundamental concepts, then the scientific conclusions we reach are more likely to be wrong. This is more than supposition: for 60 years, statisticians have warned that the scientific literature harbors misunderstandings about basic statistical concepts. Original articles published in 1996 by the American Physiological Society’s journals fared no better in their handling of basic statistical concepts. In this review, we summarize the two main scientific uses of statistics: hypothesis testing and estimation. Most scientists use statistics solely for hypothesis testing; often, however, estimation is more useful. We also illustrate the concepts of variability and uncertainty, and we demonstrate the essential distinction between statistical significance and scientific importance. An understanding of concepts such as variability, uncertainty, and significance is necessary, b...
Evidence Based Library and Information Practice, 2008
Objective – This article measures the extent of the synonym problem in full-text searching. The s... more Objective – This article measures the extent of the synonym problem in full-text searching. The synonym problem occurs when a search misses documents because the search was based on a synonym and not on a more familiar term. Methods – We considered a sample of 90 single word synonym pairs and searched for each word in the pair, both singly and jointly, in the Yahoo! database. We determined the number of web sites that were missed when only one but not the other term was included in the search field. Results – Depending upon how common the usage is of the synonym, the percentage of missed web sites can vary from almost 0% to almost 100%. When the search uses a very uncommon synonym ("diaconate"), a very high percentage of web pages can be missed (95%), versus the search using the more common term (only 9% are missed when searching web pages for the term "deacons"). If both terms in a word pair were nearly equal in usage ("cooks" and "chefs"), t...
Length-biased sampling exists in screening programs where longer duration disease is detected dur... more Length-biased sampling exists in screening programs where longer duration disease is detected during the preclinical stage because a longer sojourn time (preclinical duration) has a higher probability of being screen detected. By modeling the course of disease, we quantify the effect of length-biased sampling on clinical duration when cases are subject to periodic screening with variable test sensitivity. We use the highly flexible bivariate lognormal density to jointly model preclinical and clinical durations, and we model screening test sensitivity as a function of the sojourn time and number of previous false negative screens. We show that the mean clinical duration among screen-detected cases can be up to 40% higher, with shrinking standard deviation, than those among nonscreen-detected cases, due to biased sampling alone, irrespective of any possible benefit (increased survival time arising from earlier detection or reduction in mortality). These findings will aid in the design and interpretation of screening trials.
ABSTRACT We develop a probability model for evaluating long-term effects due to regular screening... more ABSTRACT We develop a probability model for evaluating long-term effects due to regular screening. People who take part in cancer screening are divided into four mutually exclusive groups: True-early-detection, No-early-detection, Overdiagnosis, and Symptom-free-life. For each case, we derive the probability formula. Simulation studies using the HIP (Health Insurance Plan for Greater New York) breast cancer study data provide estimates for these probabilities and the corresponding credible intervals. These probabilities change with a person’s age at study entry, screening frequency, screening sensitivity, and other parameters. We also allow the human life time to be subject to a competing risk of death from other causes. The model can provide policy makers with important information regarding the distribution of individuals participating in a screening program who eventually fall into one of the four groups.
Proceedings of the Royal Society B: Biological Sciences, 2014
Developmental responses to nutritional variation represent one of the ecologically most important... more Developmental responses to nutritional variation represent one of the ecologically most important classes of adaptive plasticity. However, knowledge of genome-wide patterns of nutrition-responsive gene expression is limited. Here, we studied genome-wide transcriptional responses to nutritional variation and their dependency on trait and sex in the beetle Onthophagus taurus. We find that averaged across the transcriptome, nutrition contributes less to overall variation in gene expression than do sex or body region, but that for a modest subset of genes nutrition is by far the most important determinant of expression variation. Furthermore, our results reject the hypothesis that a common machinery may underlie nutrition-sensitive development across body regions. Instead, we find that magnitude (measured by number of differentially expressed contigs), composition (measured by functional enrichment) and evolutionary consequences (measured by patterns of sequence variation) are heavily d...
This paper presents and develops three approaches for evaluating the degree of "homogeneity" or "... more This paper presents and develops three approaches for evaluating the degree of "homogeneity" or "randomness" present in a two-dimensional material. Such problems of detecting homogeneity arise in several technological, biological and geological applications. The first approach defines the concept of a "cluster" and develops some test statistics based on the number of clusters and their size distribution. The second approach divides the material into blocks and then applies a nonparametric analysis of variance to these blocks. The third approach employs a graph-theoretic model, in which the length of a certain minimum spanning tree is used as a measure of homogeneity. These approaches are compared using simulation experiments, and are then applied to a problem from materials science.
Frequently, a sample may contain observations that differ substantially from the other data value... more Frequently, a sample may contain observations that differ substantially from the other data values. There are various ways to deal with the possibility of such values so that the resulting analysis will not be adversely affected if they are present. All of these methods assign weights to observations according to some well-conceived algorithm. In this article we concentrate on two forms of assigning weights to observations. The first is trimming, which corresponds to assigning zero weight to a prespecified fraction of the extreme observations and equal weights to the rest. The second is Winsorizing, which also assign zero weights to the extreme observations, as in trimming, but assigns extra weight to the most extreme observations in the retained sample. In this article we will define these concepts for a single sample of observations, and briefly discuss the applications to more complex problems like regression.
Editor's Note: This article is one of two that will be presented orally at the Technometrics... more Editor's Note: This article is one of two that will be presented orally at the Technometrics session of the 38th Annual Fall Technical Conference, to be held in Birmingham, Alabama, October 20-21, 1994. The conference is cosponsored ...
Screening for a disease such as cancer is often regarded as a beneficial and successful strategy ... more Screening for a disease such as cancer is often regarded as a beneficial and successful strategy for reducing mortality. However, as with any clinical treatment or intervention, benefit cannot be assumed, and screening can entail both costs and harms, so the screening as a ‘treatment’ must undergo evaluation. An evaluation requires a definition of the treatment ‘benefit’, design of studies to measure that benefit with as little bias and variance as possible, and the development of methods for estimating the potential benefit. In screening studies, the factors most central to the evaluation are unobservable (e.g. earliest point in time at which disease becomes detectable, or ‘preclinical’; time at which disease might have been detected in the absence of screening; test sensitivity). Thus, screening programs should be evaluated on scenarios in which these factors are varied, to ensure the robustness of the estimated benefit under a variety of circumstances. This article describes the ...
Screening tests are used frequently for control of diseases such as cancer. The increased surviva... more Screening tests are used frequently for control of diseases such as cancer. The increased survival time of screen‐detected cases over those that are detected clinically may be due in part to ‘lead time’, or the length of time by which the disease is diagnosed earlier by screening in the presence or absence of any real extension in survival time. A realistic evaluation of screening needs to assess the true benefit of screening; that is, the length of time by which survival has been extended, beyond merely the time of the advanced diagnosis. The comparison of survival measured from time of entry between cases in a screening arm and in a control arm in randomized studies avoids the lead time bias. If the effects of average lead time and average benefit on survival are additive, these effects can be estimated by recognizing that (a) the difference in survival curves since time of diagnosis confounds benefit and lead time, but (b) the difference in survival curves since time of start of ...
Randomized screening trials provide the optimal means of assessing the benefit of screening for c... more Randomized screening trials provide the optimal means of assessing the benefit of screening for cancer and other chronic diseases. Unlike therapy trials, however, where strict eligibility criteria assure the comparability of cases of disease in the arms of the trial, the cancer cases identified during follow‐up are a subset of all randomized participants. Furthermore, those cases detected by screening tend to arise from length biased sampling which also can bias estimates of the screening benefit and of average lead time. To reduce or eliminate this bias, we propose several methods for defining comparable groups of cases from the trial arms. We examine, via simulation, these methods with respect to their effects on (i) point and interval estimates of average lead time and average benefit time and (ii) the logrank test statistic for a mortality effect of screening. The most successful new method for defining comparable case groups uses an estimate of the mean sojourn time (mean precl...
Detecting patterns in health-related data for geographic areas is facilitated with the use of exp... more Detecting patterns in health-related data for geographic areas is facilitated with the use of exploratory methods, especially smoothing. In addition, these data often must be adjusted for known prognostic factors such as age and gender. The analysis in this paper focuses on mortality rates due to malignant melanoma in White males and White females; these data are adjusted for both age and latitude, separately for males and females, and then smoothed using (a) a non-linear smoother known as weighted head-banging, and (b) a new method that incorporates the adjustment and the smoothing simultaneously. Maps of the continental United States show regions of high rates, even after having adjusted for age and latitude, and suggest the possibility of other variables that may influence the rates.
John Tukey's impact on statistics, and on science in general, is broad and lasting. This article ... more John Tukey's impact on statistics, and on science in general, is broad and lasting. This article discusses some of these contributions, with a special emphasis on those that led to the development of robust methods and data exploration. In view of today's emphasis on data mining techniques, the recollection of Tukey's influence is especially timely.
Large-scale strategies are needed to reduce overuse of antibiotics in US communities. To evaluate... more Large-scale strategies are needed to reduce overuse of antibiotics in US communities. To evaluate the impact of a mass media campaign-&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;Get Smart Colorado&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;-on public exposure to campaign, antibiotic use, and office visit rates. Nonrandomized controlled trial. Two metropolitan communities in Colorado, United States. The general public, managed care enrollees, and physicians residing in the mass media (2.2 million persons) and comparison (0.53 million persons) communities. : The campaign consisting of paid outdoor advertising, earned media and physician advocacy ran between November 2002 and February 2003. Antibiotics dispensed per 1000 persons or managed care enrollees, and the proportion of office visits receiving antibiotics measured during 10 to 12 months before and after the campaign. After the mass media campaign, there was a 3.8% net decrease in retail pharmacy antibiotic dispenses per 1000 persons (P = 0.30) and an 8.8% net decrease in managed care-associated antibiotic dispenses per 1000 members (P = 0.03) in the mass media community. Most of the decline occurred among pediatric members, and corresponded with a decline in pediatric office visit rates. There was no change in the office visit prescription rates among pediatric or adult managed care members, nor in visit rates for complications of acute respiratory tract infections. A low-cost mass media campaign was associated with a reduction in antibiotic use in the community, and seems to be mediated through decreases in office visits rates among children. The campaign seems to be cost-saving.
Journal of the American Statistical Association, 1982
Kafadar: A Biweight Approach to the One-Sampie Problem 417 in Lax (1975, as referenced in Mostell... more Kafadar: A Biweight Approach to the One-Sampie Problem 417 in Lax (1975, as referenced in Mosteller and Tukey 1977, p. 207). In terms of their average values, ave(iw) and ave(i<0)) approach cr and (2/3)cr, respectively, as n ...
Earlier work by Saha et al. rigorously derived a general probabilistic model for the PCR process ... more Earlier work by Saha et al. rigorously derived a general probabilistic model for the PCR process that includes as a special case the Velikanov-Kapral model where all nucleotide reaction rates are the same. In this model the probability of binding of deoxy-nucleoside triphosphate (dNTP) molecules with template strands is derived from the microscopic chemical kinetics. A recursive solution for the probability function of binding of dNTPs is developed for a single cycle and is used to calculate expected yield for a multicycle PCR. The model is able to reproduce important features of the PCR amplification process quantitatively. With a set of favorable reaction conditions, the amplification of the target sequence is fast enough to rapidly outnumber all side products. Furthermore, the final yield of the target sequence in a multicycle PCR run always approaches an asymptotic limit that is less than one. The amplification process itself is highly sensitive to initial concentrations and the reaction rates of addition to the template strand of each type of dNTP in the solution. This paper extends the earlier Saha model with a physics based model of the dependence of the reaction rates on temperature, and estimates parameters in this new model by nonlinear regression. The calibrated model is validated using RT-PCR data.
Background. The effect of urbanization on age-adjusted lung cancer mortality rates in US counties... more Background. The effect of urbanization on age-adjusted lung cancer mortality rates in US counties is investigated. The data come from National Cancer Institute, and urban trends are estimated in time periods 1970-1979 and 1980-1987, for both white males and white females. To account for possibly different gradients in different parts of the country, the 48 contiguous states are divided into seven regions. Methods. A measure of urbanness, urbanicity, is defined and is used to stratify counties. A multiplicative model is proposed that relates county mortality rates to urbanicity. The residuals from this multiplicative model serve as age-and urbanadjusted rates. Results. Urban-rural gradients are significant for nearly all regions for both white males and white females, diminishing slightly in the latter time period for white males but becoming stronger for white females. Conclusions. The age-and urban-adjusted rates may be used in mapping to investigate geographical patterns that remain after removal of the urban factor.
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Papers by Karen Kafadar