Download presentation

Presentation is loading. Please wait.

Published byAldo Cameron Modified over 3 years ago

1
Random vs. systematic sampling J. Gallego, MARS AGRI4CAST

2
Geographic systematic sampling Positive More efficient than random sampling if the spatial autocorrelation is a decreasing function of the distance More difficult to manipulate: it gives more confidence Important if the results are politically sensitive

3
Geographic systematic sampling (2) Negative It may introduce a distortion in the variance if the landscape is repetitive Chess board effect if the size and orientation of the cells is the same as the sampling step This can be an issue in small pilot regions Unlikely in large complex regions There is no unbiased estimator of the variance The usual variance estimators are conservative (overestimate the variance)

4
Variance estimation in LUCAS Usual variance estimator for two-phase random sampling (incomplete stratification) The estimated variance of Y in stratum h can be written This estimator is strongly biased for systematic sampling The bias is reduced with a local estimator of the variance of Y:

5
Example of sophisticated sampling scheme TREES-2: estimation of tropical deforestation Very efficient in terms of variance, but strongly attacked in the political forum

6
Alternative by FAO for general land cover monitoring One tile of 10x10 or 20x20 km each lat-long degree Half-rate above 60º Problem of bias Less problematic in tropical countries

Similar presentations

OK

Lecture 14 Dustin Lueker. 2 Inferential statistical methods provide predictions about characteristics of a population, based on information in a sample.

Lecture 14 Dustin Lueker. 2 Inferential statistical methods provide predictions about characteristics of a population, based on information in a sample.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on sports day at school Ppt on 3d printing technology Ppt on single entry system Ppt on sources of energy for class 8th physics Ppt on formation of company for class 11 Download maths ppt on circles for class 9 Ppt on obesity prevention and awareness Download free ppt on child labour Free ppt on minimum wages act 1948 Ppt on conservation of wildlife and natural vegetation of brazil