a workshop on using r to select a sample for ehes

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A workshop on using R to select a sample for

EHES

Susie Cooper & Johan Heldal

Statistics Norway

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Overview• What is R and why use it?• Practical Exercises

1. Installing and loading R and packages2. Reading external files3. Calculating sample sizes4. Stage 1 - Selecting Primary Sampling Units (PSU)5. Stage 2 - Selecting Secondary Sampling Units (SSU)

• Where to get more information

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Why use R for EHES?• It has been agreed with EU because

• It’s free - therefore available for all countries involved.

• Very flexible• Very powerful and fast tool for sampling

and analyses.However…• There can be a steep learning curve to

using the program.• No user-friendly interface.

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What is EHESsampling?• A tool for planning the sampling

design• Can be used to find good stratifications• Can calculate cost-variance optimal

sample sizes within PSUs.• Can calculate costs and variances of

alternatives.• A tool for taking a probability sample

from a sampling frame.

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Using EHESsampling• The EHESsampling manual• Before using EHESsampling you have to

prepare some input datasets from the main sampling frame. For sampling at stage 1 you need• A dataset describing the PSUs• A dataset describing the strata

For stage 2 you need • The main sampling frame describing the

individual units

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1. Loading Packages• Load the EHESsampling package and

other necessary packages each time you re-open R:

library(EHESsampling)

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2. Reading External Files

• Open a new script by selecting File and New script

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2. Reading External Files

• Set the working directory where data files are stored by typing into the new script:

setwd("X:/120/EHES/R/Data")

• Then press + R to send the line to the console

Location on your computer where the data files are stored

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2. Reading External Files

• Read in the chosen file and save it in the working environment.

PSUs.df<-read.table("post1000.csv", sep=";", dec=",", header=T)

• The file is now stored as PSUs.df for this session.

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• To see the start of the data set type:head(PSUs.df)

2. Reading External Files

Print the first 6 lines of this

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Further Sampling Steps• Read in the strata dataset• Calculate the PSU sample sizes• Take a sample of PSUs – stage 1• Merge the selected PSUs with the

main sampling frame containing individual units.

• Sample individual units – stage 2

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Selected Individuals

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Help!• EHESsampling manual available at:

www.ehes.info • EHES participant manual – Part 1: Chapter

05• R websites:

• R official site: www.r-project.org• Quick R: www.statmethods.net

• Us:• Johan.Heldal@ssb.no• Susie.Cooper@ssb.no