Peter A. Rogerson

Spatial Analysis and GIS

Keywords: integration of GIS Reference Record created on 2005-06-20, modified on 2016-08-08

Positional Accuracy of Geocoded Addresses in Epidemiologic Research

Background Geographic information systems (GIS) offer powerful techniques for epidemiologists. Geocoding is an important step in the use of GIS in epidemiologic research, and the validity of epidemiologic studies using this methodology depends, in part, on the positional accuracy of the geocoding process. Methods We conducted a study comparing the validity of positions geocoded with a commercially available program to positions determined by Global Positioning System (GPS) satellite receivers. Addresses (N = 200) were randomly selected from a recently completed case–control study in Western New York State. We geocoded addresses using ArcView 3.2 on the GDT Dynamap/2000 U.S. Street database. In addition, we measured the longitude and latitude of these addresses with a GPS receiver. The distance between the locations obtained by these two methods was calculated for all addresses. Results The distance between the geocoded point and the GPS point was within 100 m for the majority of subject addresses (79%), with only a small proportion (3%) having a distance greater than 800 m. The overall median distance between GPS points and geocoded points was 38 m (90% confidence interval [CI] = 34–46). Distances were not different for cases and controls. Urban addresses (median = 32 m; CI = 28–37) were slightly more accurate than nonurban addresses (median = 52 m; CI = 44–61). Conclusions. This study indicates that the suitability of geocoding for epidemiologic research depends on the level of spatial resolution required to assess exposure. Although sources of error in positional accuracy for geocoded addresses exist, geocoding of addresses is, for the most part, very accurate.

GIS and spatial analytical problems

Abstract Increasingly, methods of spatial analysis are being integrated within geographical information systems. As this integration occurs, it is important to ensure that, (i) users of GIS recognize the limitations of spatial analysis, (ii) researchers continue to work on removing the existing impediments to accurate spatial analysis, and (iii) developers of GIS consider these limitations. In this article we discuss eight general impediments that arise in spatial analyses that span a diverse range of substantive applications. Geographical information systems offer not only the opportunity to integrate various methods of spatial analysis, but also the chance to learn more about the underlying impediments.

Elderly Parents and the Geographic Availability of their Adult Children

Using data from the 1987 National Survey of Families and Households, this study examines the distribution and determinants of the geographic distance between elderly parents and their adult children. The majority of elderly Americans have at least one adult child living within 10 miles of their residence; for those with two or more adult children, the second-closest child is usually within 30 miles. Compared with the urban elderly, rural elders live farther from their second closest-children. Daughters live no closer than sons to their parents. The analysis shows that education and number of children are the most important factors in predicting parent-child proximity. Other factors, such as age, health, and the family size of the closest adult child, are also important.

Monitoring point patterns for the development of space–time clusters

Existing statistical methods for the detection of space–time clusters of point events are retrospective, in that they are used to ascertain whether space–time clustering exists among a fixed number of past events. In contrast, prospective methods treat a series of observations sequentially, with the aim of detecting quickly any changes that occur in the series. In this paper, cumulative sum methods of monitoring are adapted for use with Knoxs space–time statistic. The result is a procedure for the rapid detection of any emergent space–time interactions for a set of sequentially monitored point events. The approach relies on a ‘local’ Knox statistic that is useful in retrospective analyses to detect when and where space–time interaction occurs. The distribution of the local Knox statistic under the null hypothesis of no space–time interaction is derived. The retrospective local statistic and the prospective cumulative sum monitoring method are illustrated by using previously published data on Burkitts lymphoma in Uganda.

Surveillance systems for monitoring the development of spatial patterns

Statistical methods concerned with the identification of temporal patterns may be classified into those that examine retrospectively a set of observations, and those that constitute surveillance systems that monitor changes as new observations become available. A similar distinction applies to the identification of geographical patterns in spatial data. There has been a notable lack of attention given to the surveillance of spatial pattern. This paper concerns development of a cumulative sum statistic and procedure for the monitoring of spatial pattern, and its application to both simulated data and to data on Burkitts lymphoma in Uganda.

Changes in geographic proximity between parents and their adult children

This study employs a weighted sample of 2173 respondents aged 60 years and older who had at least one surviving adult child and valid distance measurements from both panels of the US National Survey of Families and Households. The aim is to examine the joint effects of each generations structural characteristics on the likelihood of distance moves. Distance moves include changes due to convergence (reduced distance to the closest child) and divergence (increased distance from the closest child) or no change. Proximity accounts for potential parent moves child moves or both moves. The degree of change beyond 36 miles is not a consideration. The analysis follows and expands the models of Silverstein on general life cycle migration. The model is expanded to take into consideration the characteristics of adult children (onset of widowhood and changes in functional physical limitations). It is assumed that the closest adult child is the same at first and second observation. Berks two stage method is used in the multinomial logistic model construction. The results show that economic well being and marital status were related to changes in geographic proximity. About 12.2% lived closer and 15.2% lived farther away at the second observation. Respondents who lived within 10 miles were the least likely to change distances. Of those elderly who lived within 11-35 miles of their closest adult child 44.6% changed the distance 33% moved closer and 11.6% moved farther away. 24.8% of the elderly moved between the surveys. 36.4% of the elderly did not move and had at least one child move. The likelihood of a reduced distance to the closest child (convergence) increased with an increase in functional limitations and widowhood. The higher the level of education and income the greater the likelihood of either convergence or divergence. Longer housing tenure by the elderly was related to lower likelihood of convergence. Increases in disability and a shift to widowhood had a statistically significant impact on decisions to live with a child and to move closer to a child. Living with a child was related to higher educational level and having more children. Living in a nonmetropolitan area reduced the likelihood. Demographic characteristics of respondents and children were not strong predictors of a change in geographic proximity.

An Empirical Comparison of Edge Effect Correction Methods Applied to K -function Analysis

This paper explores various edge correction methods for K-function analysis via Monte Carlo simulation. The correction methods discussed here are Ripleys circumference correction, a toroidal correction, and a guard area correction. First, simulation envelopes for a random point pattern are constructed for each edge correction method. Then statistical powers of these envelopes are analyzed in terms of the probability of detecting clustering and regularity in simulated clustering/regularity patterns. In addition to the K-function, K(h), determined for individual distances, h, an overall statistic k is also examined. A major finding of this paper is that the K-function method adjusted by either the Ripley or toroidal edge correction method is more powerful than what is not adjusted or adjusted by the guard area method. Another is that the overall statistic k outperforms the individual K(h) across almost the entire range of potential distances h.

Case control study of the geographic variability of exposure to disinfectant byproducts and risk for rectal cancer

BackgroundLevels of byproducts that result from the disinfection of drinking water vary within a water distribution system. This prompted us to question whether the risk for rectal cancer also varies, depending upon ones long term geographic location within the system. Such a geographic distribution in rectal cancer risk would follow naturally from an association between level of byproduct and rectal cancer risk. We assess the effects of estimated geographic variability in exposure to some of the components of the trihalomethane group of disinfectant byproducts (DBPs) on the odds ratios and probabilities for rectal cancer in white males in a case control study of 128 cases and 253 controls, conducted in Monroe County, Western New York State, U.S.A. The study was designed around health data initially collected at the University at Buffalo (Department of Social and Preventative Medicine) as part of the Upstate New York Diet Study, and trihalomethane (THM) data collected from a separate independent study of THMs conducted by Monroe County Department of Health. Case participants were chosen from hospital pathology records. The controls are disease-free white males between 35–90 years old, living in Monroe County, and chosen from control groups for studies from cancer of five other (unrelated) sites. Using a combination of case control methodology and spatial analysis, the spatial patterns of THMs and individual measures of tap water consumption provide estimates of the effects of ingestion of specific amounts of some DBPs on rectal cancer risk. Trihalomethane (THM) data were used to spatially interpolate levels at the taps of cases and controls, and odds ratios were estimated using logistic regression to assess the effects of estimated THM exposure dose on cancer risk, adjusting for alcohol, dietary beta carotene intake, tap water intake, and total caloric intake.ResultsTrihalomethane levels varied spatially within the county; although risk for rectal cancer did not increase with total level of trihalomethanes, increasing levels of the component bromoform (measured in ug/day) did correspond with an increase in odds ratios (OR = 1.85; 95% CI = 1.25 – 2.74) for rectal cancer. The highest quartiles of estimated consumption of bromoform (1.69–15.43 ug/day) led to increased risk for rectal cancer (OR = 2.32; 95% CI = 1.22–4.39). Two other THMs were marginally associated with an increase in risk – chlorodibromomethane (OR = 1.78, 95% CI = 1.00–3.19) and bromodichloromethane (OR = 1.15; 95% CI = 1.00–1.32).ConclusionLevels of THMs in the water distribution system exhibited spatial variation that was partially due to variation in water age. We also observed a geographic pattern of increased risk of rectal cancer in areas with the highest levels of bromoform in the county.

Population distribution and redistribution of the baby-boom cohort in the United States: Recent trends and implications

Over 70 million people were born into the baby-boom cohort between 1946 and 1964. Over 65 million of these individuals are presently alive, and thus the cohort continues to exert a powerful influence on regional population change in the United States. In this article, we examine the recent and current geographic distribution of the baby-boom cohort. In 1990, the members of the cohort comprised a particularly high proportion of the population in a small number of dynamic metropolitan areas. We also highlight the recent migration trends exhibited by this cohort; these trends are potentially important early indicators of the retirement-related migration patterns that the cohort might follow. The spatial redistribution of the cohort has many implications, including potentially significant consequences for intergenerational relationships and caregiving. Also highlighted in the article are the temporal and geographical implications for intergenerational caregiving. There has been much attention given to the “sandwich” generation, with its members having dual caregiving responsibilities to both parents and children. A more appropriate designation may be the “stretched” generation, because caregiving seems to extend over a long period. In particular, many members of the baby-boom cohort are beginning to care for their aging parents just as they finish child rearing.