Post-Stratification as a Bias Reduction Technique

Anganuzzi, Alejandro; Buckland, Stephen T.

doi:10.2307/3809085

Cited by 13 publications

(7 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Stratification can be carried out before the survey takes place, when a priori information is available. Alternatively, post‐stratification might be used, either based on ancillary data, such as habitat categories, collected during the survey (e.g., Marques et al, 2001) or, with care, using the primary sightings data from the survey (e.g., Anganuzzi and Buckland, 1993). When object density is low, however, small sample sizes may preclude stratification or result in biased estimates of f (0), and hence of density, if stratification is carried out.…”

Section: Introductionmentioning

confidence: 99%

Incorporating Covariates into Standard Line Transect Analyses

Marques¹,

2003

Self Cite

View full text Add to dashboard Cite

An implicit assumption of standard line transect methodology is that detection probabilities depend solely on the perpendicular distance of detected objects to the transect line. Heterogeneity in detection probabilities is commonly minimized using stratification, but this may be precluded by small sample sizes. We develop a general methodology which allows the effects of multiple covariates to be directly incorporated into the estimation procedure using a conditional likelihood approach. Small sample size properties of estimators are examined via simulations. As an example the method is applied to eastern tropical Pacific dolphin sightings data.

show abstract

Section: Introductionmentioning

confidence: 99%

Incorporating Covariates into Standard Line Transect Analyses

Marques¹,

2003

Self Cite

View full text Add to dashboard Cite

show abstract

“…Density estimates were computed for each habitat type classified during fieldwork by means of stratification [38,50], since the density gradient for river dolphins is known to be greater in some river areas [40,41,10,18]. Additionally, geographic post-stratification of the study area into stratum in relation to the Tucuruí dam (downstream, reservoir 1, reservoir 2, upstream) allowed us to investigate the potential effect of the heterogeneity of densities across the study area, which are expected to occur because of substantial differences in the habitat across the sub-regions [51,50,48,52].…”

Section: Discussionmentioning

confidence: 99%

On the brink of isolation: Population estimates of the Araguaian river dolphin in a human-impacted region in Brazil

Paschoalini

Almeida

Trujillo³

et al. 2020

PLoS ONE

View full text Add to dashboard Cite

Populations of freshwater dolphins are declining in response to increased human pressure, including habitat degradation, overfishing, bycatch, poaching and obstruction of free-flowing river corridors by dams. At least three river dolphin species occur in South America: the Amazonian river dolphin, or boto (Inia geoffrensis), the Bolivian river dolphin (Inia boliviensis) and the tucuxi (Sotalia fluviatilis). A fourth species, the Araguaian boto (Inia araguaiaensis), been proposed for the Tocantins-Araguaia, a large river basin in northern Brazil. Here we show that the Araguaian boto population in the Tocantins River is relatively small (N = 1083, CV = 0.52). During a survey to estimate density and abundance, 138 groups (198 individuals) of botos were observed along a~600 km stretch of the Tocantins River in five different habitats (river margin, river channel, channel, island margin, and a dam reservoir). Overall, lower densities of the Araguaian boto were registered downstream of the Tucuruí dam, the world's fifth largest hydropower dam. Density was 68% lower in the river margin habitat downstream (0.23 ind./km 2 , CV = 0.92) than upstream (0.72 ind./km 2 , CV = 0.53). In addition, density within the Tucuruí reservoir decreases from upstream areas towards the dam. Geographic post-stratification of data into sub-regions (downstream, reservoir, upstream) in relation to the Tucuruí dam helped to reduce CV by~70%, which illustrates the high variability in the encounter rate in these areas. Our findings suggest that the Araguaian boto population has been impacted by the construction of the Tucuruí dam. The construction of other dams proposed for the Tocantins-Araguaia basin should be planned strategically to a1111111111 a1111111111 a1111111111 a1111111111 a1111111111

show abstract

“…When telemetry data are unavailable, RSFs developed for survey blocks using previous data from longterm series of surveys may be an alternative in areas where detection bias is minimal. In these situations, there is also the opportunity to include annual variation in environmental conditions, such as snow cover, in the prestratification and sample unit selection at the time of the surveys or even with poststratification (Anganuzzi and Buckland 1993).…”

Section: Discussionmentioning

confidence: 99%

Using Resource Selection Functions to Improve Estimation of Elk Population Numbers

et al. 2008

View full text Add to dashboard Cite

Stratification is commonly used to improve sampling efficiency of aerial surveys of ungulate populations with strata typically based on a priori information, such as preflight animal observations or vegetation attributes as surrogates for animal densities. We evaluated the usefulness of stratifying survey units for elk (Cervus elaphus) in the Rocky Mountain foothills of Alberta, Canada, using a resource selection function (RSF). We compared precision and design efficiency (DEFF) of population estimates from stratification approaches based on an RSF model to the past approach using amount of forest cover. We used a sample of telemetry relocations taken over a 3‐year period from 165 elk, rarified to times of the day and months of the year when aerial surveys are conducted, to develop the RSF. We then used the top RSF model, based on Akaike's Information Criterion, to derive the average RSF value for an 8‐km2 survey unit. Using survey data from the first year, we evaluated binning schemes to define RSF‐oriented strata based on poststratification and showed that Jenks natural breaks in the RSF values provided the greatest improvement in DEFF and increased precision, compared to 2 other stratification schemes. We then used this approach with data from 2 additional surveys to find that stratification by RSF consistently improves relative precision and design efficiency of elk population estimates, whether we employ pre‐ or poststratification. Where a RSF is available it could be used as a surrogate for animal densities when conducting stratified sampling for population surveys.

show abstract

Post-Stratification as a Bias Reduction Technique

Cited by 13 publications

References 8 publications

Incorporating Covariates into Standard Line Transect Analyses

Incorporating Covariates into Standard Line Transect Analyses

On the brink of isolation: Population estimates of the Araguaian river dolphin in a human-impacted region in Brazil

Using Resource Selection Functions to Improve Estimation of Elk Population Numbers

Contact Info

Product

Resources

About