SADC Course in Statistics

The Swaziland area survey

Choice Ginindza

Overview

• Annual crop-cutting survey

• Concentrate on the measurement of areas– under each crop

• Forms for collection

• What happens to the data– after they have been collected

Each enumerator has a copy of this

guide

Holding layout sketch plan

Field 1 Maize

Field 2 60% maize,

40% pumpkins

Field 4 maize

Field 3 beans

Symbols for the sketch plan

Field area measurements

1 2 2 0 1 0 5 2

0 1

125 50 27.5

0.85

113 100

0.25

112 60 139 40

Area in each field

01 Maize 100% 113 0.85 02 M 60% Pk 40% 112 139 03 Beans 100% 131 0.53 04 Maize 100% 113 0.98

Total crop area

0.151.83

0.610.53

Other information is also recorded

Plus household information

What happens next?

• 75 staff collect these area data• between November and January each year

• The completed forms are sent to me in HQ– there are about 2000 forms each year– it is one form per household, unless a household

has more than 12 fields

• The forms are checked for consistency – before being sent for data entry

• They are then sent for data entry– By the end of January

Then – the data are entered

• Special software is used for the data entry– It is called CSPRO– and is designed specially for data entry

• A headquarters' staff member– has programmed CSPRO– to make the data entry screen – the same as the data entry form

• There are 7 staff – in the Government data entry team– and I add 2 of my staff just for this work

• It takes about 2 weeks

Checking the data once entered

• The resulting computer files – are returned to me

• I first look at them in an editor– it is called OX-edit and is just like Notepad– that is on every computer

• I use the editor to look for “shifts” – in the data from CSPRO– one character missing can make the transfer – to Excel or a statistics package very odd

• That checking just takes an hour perhaps

The data now

• Then I open the data in SPSS– That is a commonly used statistics package

• They look the same in Excel – – as shown on the next slide

• There are now 3945 records, – each one is a crop within a household.

• Plus the household information

Crop area information

Household information

Checking in SPSS

• I check the data in SPSS– That typically takes one day

• I also have the paper records available– And check odd values against them

• I correct in SPSS (and Ox-Edit)

• Sometimes records are returned – to the data entry people– and there is a further round

• Typically we find problems with 10 to 30 records

Analysis

• Now I analyse the data using SPSS

• That takes perhaps 1 day

• The most important is maize, – so that is done first.

• I get results from each Enumeration area

• And then total them for each district

• I compare with the previous year – as another check

• I then export the summaries from SPSS to Excel

Results

• Here is the sort of table I get.

Reporting

• This information is then sent – to our Meteorological Service

• They have to be there by the end of February

• The met service estimates yields

• And these estimates are multiplied – by these areas

• To give the estimated production

Publishing

• The estimates are then in a monthly– agroclimatic bulletin

• Which is part of our NEW system– NEW = National Early Warning

• to provide the food-balance sheet– for the current year

• Later we produce our own report– once we have the yields as well