Spatial variability of soil organic carbon (SOC) of different land use patterns and soil types was examined in a county-wide red soil region of South China, using six sampling densities, 14, 34, 68, 130, 255, and 525 samples designed by the method of grid sampling in 6 different grid sizes, labeled as D14, D34, D68, D130, D255, and D525, respectively.
The specially commissioned sampler, designed by the OMM editorial team and Guardian Creative will feature new material and highlights from the magazine.
We avoid any bias due to data collection and/or sample design by using this approach.
These procedures allow incorporating the sample design by specifying the age-ethnicity strata and sampling weights.
20 All analyses allowed for the clustered, stratified sample design by using the "survey commands" in Stata version 11.
Because the ratio of sample size to population size was small, we approximated the sample design by a "with-replacement" design for purposes of variance estimation in SUDAAN.
All of our models use robust standard errors which adjust for this complex sample design by clustering at the PSU level.
We accounted for the clustering of observations and study sample design by specifying three nested random-effect terms, one for each sample "level", geographic region, University/city, and school, confirming their inclusion by a Likelihood Ratio (LR) "chunk" test [ 41] and a p-value criterion of <0.2.
We conducted a two-stage cluster sample design by administering a questionnaire on AIDS health awareness to senior high school students from three coastal cities to survey HIV/AIDS related information, motivation, behavioral skills and sexual behaviors from three coastal cities.
