Systematic survey

Systematic survey

Description of the algorithms

We use the same algorithms as the simple random sampling without discount.
The difference being of course the selection of the sample. We use the same principles for calculating total and proportions to finish on statistical evaluation of the results.

Selection algorithm

The selection algorithm , which is close to the selection algorithm of a survey
simple random without replacement, is as follows (example 220 ​​samples):

/* echantillonage Sas sur les  echantillons */!
proc surveyselect data=tPres2007 method=SYS n=220 !                
reps=50 seed=1213  out=sasPres2007 stats;!
run;

We use the procedure sas " SURVEYSELECT " by selecting the " SYS " method. The algorithm selects the units to a fixed interval . The size of the interval is
calculated by N / n . Here the interval is : 297 . Every 297 samples , the algorithm
selected value. The starting value which is therefore between 1 and 297 is selected at random . The selection is made ​​equal probability (n / N) and without replacement.
We used the " rep " parameter to generate 50 replications and the seed for the random generation 1213.Ceci we generate 50 * 220 pooled samples in the
dataset " sasPres2007 ." The "stats" variable we used then to calculate the total with
the procedure " surveymean ." code is the same for the circulation of 500 samples with the difference that "n" is 500.

Results Of 220 samples

Comment samples and detailed results of Ségolène Royal

Mean = 0.46883, standard deviation = 0.00731 confidence interval 95% CI = [0.46675, 0.47091] 

The accuracy of this draw is immediately more accurate than simple random sampling without replacement equal size survey. 

The effect of sampling is 0.73. We won almost 26% difference - the type of the result. 

Comment and detailed results of Nicolas Sarkozy

Mean = 0.53117 

Standard deviation = 0.00731 

Confidence interval 95% CI = [0.52909, 0.53325] This draw gives Sarkozy winner 53.117%. This result is close to the final value 

53.04%. The variance is more accurate than simple random sampling with a sampling effect of nearly 73%.

On 500 samples

Comment and detailed results of Ségolène Royal

Mean = 0.47052 , standard deviation = 0.00425 , confidence interval 95% CI = [0 . 46931 ;

0.47173 ] I must say that by studying this distribution , it 's quickly see an effect

staircase is attached has the pulling method . The list of polling stations has not been sorted before the draw . We certainly face a sampling error,

cycle or not , even if it seems fairly obvious to determine. This can be a

explanation for this surprising result . A prior authorization by Slice of Urban Area certainly give us

a better result. The standard deviation here is smaller than the simple random sampling without replacement sample

equal size ( n = 500 ) .

The effect of this sample is 0.8 which is greater than that found on the sample size to 220 .

The Gaussian assumption seems compromised.

Comment and detailed results of Nicolas Sarkozy

Mean = 0.52948, standard deviation = 0.00425, confidence interval 95% CI = [0.52827; 

0.53069] can be found on the distribution, the opposite effect on the outcome of candidate Royal staircase 

down. The draw is not sorted according to a previously good distribution, we get this.