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Hypotheses, Variables and Sampling Methods

How psychologists plan a study: writing an aim and a null or alternative hypothesis, choosing the independent, dependent and extraneous variables, and picking participants by random, opportunity, systematic or stratified sampling.

⏱️ 16 min 🎯 14 activities
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What you'll cover

Planning a study

Before psychologists run a study, they plan it carefully. They write an aim and a hypothesis, decide which variables to change and measure, and choose how to pick their participants. This module covers hypotheses, variables and sampling methods. Getting these right makes a study fair and its results trustworthy.

Aim, hypothesis, variables

Learn these four terms before you study how research is planned.

Two kinds of hypothesis

A study states two hypotheses about its variables.

Operationalise the variables

To reach the top grades, operationalise your variables, which means writing them so they can be measured. For example, do not just say sleep; say hours of sleep per night. Always be able to point to the independent variable you change and the dependent variable you measure.

Match the term

  • independent variable
  • dependent variable
  • extraneous variable
  • null hypothesis
  • the variable the researcher changes
  • the variable the researcher measures
  • an unwanted variable that could affect the results
  • the prediction that there is no difference

Match the sampling method

  • random sampling
  • opportunity sampling
  • systematic sampling
  • stratified sampling
  • every member of the population has an equal chance of being chosen
  • the people who are available at the time are used
  • every nth person on a list is chosen
  • subgroups are chosen in proportion to the population

Find the variable

A researcher tests whether students who revise with music score differently on a test. What is the independent variable?

  • Whether the students revise with music or without it.
  • The scores the students get on the test.
  • The number of students in the study.
  • The time of day the test is taken.

A good hypothesis

An alternative hypothesis does TWO of these things. Select the TWO.

  • It predicts a difference or a relationship between the variables.
  • It is a clear statement that can be tested.
  • It lists every participant by name.
  • It proves the results before the study begins.

Draw a sample

Put the steps of choosing a sample in order, earliest first.

  • Define the target population
  • Choose a sampling method
  • Select the participants
  • Gather the sample

Independent, dependent, and the rest

The variable the researcher changes is the _____ variable. The variable the researcher measures is the _____ variable. An unwanted variable that could affect the results is an _____ variable. A hypothesis that predicts no difference is the _____ hypothesis. Choosing people so that every member of the population has an equal chance is _____ sampling.

independent dependent extraneous null random alternative opportunity systematic stratified sample

Set up a systematic sample

A researcher wants a systematic sample of 25 students from a school roll of 500 names, choosing every nth name from a random starting point. What value of n should she use?

Tap the variables

A study tests whether people who drink more water solve more puzzles. Tap the independent variable and the dependent variable.

  • the amount of water people drink
  • the number of puzzles solved
  • the researcher who runs the study
  • the room where the study happens

Name the variable

For each part of a sleep study, decide which kind of variable it is.

  • The study changes how much sleep people get. How much sleep people get is the...
  • The study measures how many words people remember. That is the...
  • Noise from outside the room might affect the results by accident. That is an...

Plan a study

A psychologist wants to find out if students who eat breakfast score higher on a memory test. Write an alternative hypothesis for this study, and name the independent variable and the dependent variable.

  • Write an alternative hypothesis that predicts a difference
  • Name the independent variable the researcher changes
  • Name the dependent variable the researcher measures