Task: Read the following summaries of studies and how they got their samples. Identify the type of sampling method used. Was it:
(a) Random
(b) Self-selected/volunteer
(c) Opportunity
Mental Health and War: A psychologist studying the effects of war on mental health got a list of all enlisted soldiers in the countries army using public census records. They assigned a number to each name and then used an online number generator to decide who to ask to participate in the study.
Cross-cultural Survey of Altruism: A cross-cultural psychologist gathered survey data on altruism by visiting big cities in 20 different countries and spending two hours in the center of each city asking people walking by if they wanted to volunteer to fill out questionnaires.
Experiment on Social Isolation and Depression: A psychology professor offered course credit for her students if they signed up to participate in an experiment on the effects of being ignored by other people.
Social Media and Interpersonal Skills: A developmental psychologist wanted to study correlations between social media and interpersonal skills so they emailed a school and asked the Principal and teachers to see who wanted to participate. Three teachers were willing to give up an hour of their teaching time so the researcher could come into the class and gather data.
Remember: Participants in an opportunity sample can still be asked to volunteer (and decline).
Bullying Bystanderism: Researchers wanted to study bystanderism towards bullying in a real-life situation so they hired child actors to pretend like one was being bullied by a group of other kids. This happened in the foodcourt of a shopping mall. The researchers sat nearby and discretely gathered data on who helped.
Twin Study: SRI International (A research centre) is seeking participants for its twin study. They gather participants by advertising on their website (check it out here).
PTSD and 9/11: (This is a real example): In a study on the effects of 9/11, researchers used a telephone database and a random phone dialler to see if there were correlations between proximity to the twin towers and the psychological effects of the attacks.
Recreational Drug Use and Academic Achievement: A psychologist in Australia wants to study effects of recreational drug use (e.g. marijuana) on student academic achievement. They posted a flyer in the “Jobs Advertised” section of the student building’s noticeboard as well as on their Facebook group and in the Uni newspaper.
Teachers: Answers can be found in the ‘Student Workbook; Teacher’s Edition’ in the Quantitative Methods Teacher’s Support Pack
The following video from Simple Learning Pro. may help give you a better grasp of different types of sampling methods.
Travis Dixon is an IB Psychology teacher, author, workshop leader, examiner and IA moderator.