Target population-> Study Population-> Sample
7
Target population-> Study Population-> Sample 1 WWW.HIVHUB.IR Target Population : All homeless in country X Study Population : All homeless in capital shelters in the Sample: Homeless at particular shelter
description
Target population-> Study Population-> Sample. Sample: Homeless at particular shelter. Study Population: All homeless in capital shelters in the . Target Population: All homeless in country X. What do we want from our sample?. - PowerPoint PPT Presentation
Transcript of Target population-> Study Population-> Sample
Slide 1
Target population-> Study Population-> Sample1WWW.HIVHUB.IRTargetPopulation:All homeless in country XStudyPopulation:All homeless in capital shelters in the Sample:Homeless at particular shelter
Principles of Sampling12/19/2009A.Mirzazadeh1What do we want from our sample?Unbiased estimates of our indicators = Low Systematic Error
Precise estimates of our indicators = Low Random Error2WWW.HIVHUB.IR
Principles of Sampling12/19/2009A.Mirzazadeh2Selection biasesSelection biases, that pose a threat to external validity3WWW.HIVHUB.IRTarget PopulationStudy PopulationNon-participants Participants Remaining partResponseNon-Response
Principles of Sampling12/19/2009A.Mirzazadeh3How to avoid selection biasesAvoiding selection bias requires a random/probability sample.
Monitoring the sampling process from the beginning to the end of the survey.
4WWW.HIVHUB.IR
Principles of Sampling12/19/2009A.Mirzazadeh4Precise estimatesParameter: the value of our variable in the whole populationStatistics: the value of a variable in the sample
Standard error: is a measure which shows how much our statistics is close to the parameter5WWW.HIVHUB.IR
Principles of Sampling12/19/2009A.Mirzazadeh5How to improve the precisionStandard error (or precision) depends upon:Size of the sample ( Total / Efficient sample size)Distribution of character of interest in the population
6WWW.HIVHUB.IR
Principles of Sampling12/19/2009A.Mirzazadeh6General ConclusionIn HIV surveillance surreys, we have to estimate relevant indicators in the whole population, and/or in the most at risk groups.Since, census is impossible, we have to measure these indicators in a sample and extrapolate the findings to the whole target populationTo increase the accuracy, we have to have an unbiased sample with reasonable sample size
7WWW.HIVHUB.IR
Principles of Sampling12/19/2009A.Mirzazadeh7
