STAT20 Questions and Data Scope

Target Population, Access Frame, Sample

As part of making the connection between the data and the topic of the investigation, we idenfity following concepts; these concepts help us understand the scope of data, and are useful whether we aim to gain a knowledge about a population, scientific quantity, physical model, or social behavior.

 

Target Population

Target population consists of the collection of elements that you ultimately intend to describe and draw conclusions about.

Here, an element is sometimes called a unit of observation.

Access Frame

Access frame is the collection of elements that are accessible to you for actual measurment. The units that you can access the target. Units in an access frame may be only a subset of the target population. Additionally, the access frame may include units that don’t belong to the target population. 

Target population에는 포함되지 않지만, access frame에는 존재하는 경우를 예시로 들어보자. 국회의원 후보 선거에서 유권자가 어느 후보를 투표하였는지 알아보기 위해 유권자들에게 전화설문을 실시한다. 이때, 우리가 전화한 유권자가 해당 선거에서 투표를 하지 않았다면, 이 유권자는 우리의 access frame에는 포함되는 반면, target population에는 포함되지 않는다.반대로, Target population에 포함되는 반면, access frame에 포함되지 않는 경우는 다음과 같다. 우리가 전화를 건 유권자가 전화설문에 응하지는 않았지만(모르는 전화를 받지 않는 사람이라 생각해보자), 투표를 했을 경우, 이 유권자는 우리의 access frame에는 존재하지 않지만, target population에 포함된다.

Sample

Sample is the subset of units taken from the access frame to measure, observe, and analyze. 

 

다음 몇가지 예시들에서 위의 개념들을 적용시켜 볼 것이다.

Example 1: Kids watching TV

The Early Childhood Longitudinal Study (ECLS) followed children who were in kindergarten in 1998 through to eighth grade. Data were collected from principals, teachers, parents, and children, and included student test scores, family demographics, school demographics, etc. When the children were in the eighth-grade in 2006, they were given a paper-and-pencil questionnaire that asked questions how they spent their time after school, among other things.

The ECLS was developed under the sponsorship of the U.S. Department of Education, and carried out by Westat and the Educational Testing Service (ETS). Children were selected through a multistage process, where geographic areas were chosen; then, within the selected regions, elementary schools (both public and private) were chosen; and at each school a sample of kindergartners were invited to participate (actually, their parents were asked permission for their children to participate). All together 21,00 kindergartners across the US participated

 

Target population:

Access frame:

Sample:

Example 2: Environmental Hazards and Health

In 2020, Johnson & Johnson carried out a clinical trial for their new COVID vaccine. They wanted to determine the efficacy of their vaccine, i.e., how much more were people with the vaccine able to resist infection from COVID-19 compared to those who did not receive any vaccine.

To answer this question, they enrolled 43,738 people in the trial. These volunteers were:

• adults 18 and over;
• participants in the study from October to November, 2020;
• from 8 countries across 3 continents, including the US and South Africa.

The participants were split into two groups at random. Half received the new vaccine, and the other half received a placebo, a fake vaccine such as a saline solution. Then, everyone was followed for 28 days to see whether they contracted COVID-19.

 

Target population:

Access frame:

Sample:

Example 3: Flights out of the Bay Area

Example 4: COVID Vaccine Trials