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Geology topics

W.A. Link

Publications and source records attributed to W.A. Link.

60 records · Page 4Linked to original sources
USGS1994

The 1992 and 1993 summary of the North American Breeding Bird Survey

Using data from the North American Breeding Bird Survey (BBS), continental and regional changes in bird populations were estimated for the 2-year periods of 1991-1992 and 1992-1993. These 2-year changes were placed in the context of population trends since 1966. During 1991-1992, 62% of all species exhibited positive continental trend estimates. For species showing significant population trends, 68 increased while 30 decreased. The percentage of species with positive continental trends was reduced to 45% during 1992-1993, when 39 species exhibited significant increases and 60 experienced significant decreases. Over the entire survey period of 1966-1993, 48% of all species showed positive trend estimates, with the number of species showing significant increases and significant decreases at 94 and 104, respectively. The continental and regional percentages were also analyzed for 12 groups of North American birds having shared life-history traits. While many regional patterns existed within these groups, the largest percentages of increasing species were generally found in the Central and Western BBS regions during 1991-1992. The smallest percentages of increasing species were generally evident in the Western BBS Region during 1992-1993.

Bird Populations↗
USGS1994

Estimating equations estimates of trends

The North American Breeding Bird Survey monitors changes in bird populations through time using annual counts at fixed survey sites. The usual method of estimating trends has been to use the logarithm of the counts in a regression analysis. It is contended that this procedure is reasonably satisfactory for more abundant species, but produces biased estimates for less abundant species. An alternative estimation procedure based on estimating equations is presented.

Bird Populations↗
USGS1993

Efficiency and optimal allocation in the staggered entry design

The staggered entry design for survival analysis specifies that r left-truncated samples are to be used in estimation of a population survival function. The ith sample is taken at time Bi, from the subpopulation of individuals having survival time exceeding Bi. This paper investigates the performance of the staggered entry design relative to the usual design in which all samples have a common time origin. The staggered entry design is shown to be an attractive alternative, even when not necessitated by logistical constraints. The staggered entry design allows for increased precision in estimation of the right tail of the survival function, especially when some of the data may be censored. A trade-off between the range of values for which the increased precision occurs and the magnitude of the increased precision is demonstrated.

Communications in Statistics - Theory and Methods↗
USGS1988

Bias of animal population trend estimates

A computer simulation study of the population trend estimator used for the Mourning Dove Call-Count Survey, Woodcock Singing Ground Survey, Breeding Bird Survey and other surveys concluded that the estimator had negligible bias in most situations but that observer covariables should not be used with less than five years of data. With rare species (e.g. two birds per route), at least five years should be used. The estimator is seriously biased towards not detecting population changes with very rare species (e.g. 0.3 birds per route). Other technical recommendations are made.

Book chapter↗
USGS1988

An identifiable model for informative censoring

The usual model for censored survival analysis requires the assumption that censoring of observations arises only due to causes unrelated to the lifetime under consideration. It is easy to envision situations in which this assumption is unwarranted, and in which use of the Kaplan-Meier estimator and associated techniques will lead to unreliable analyses.

Book chapter↗