11.1.5 Methods of Sampling & 6 Experimental Designs

What are Sample Bias and Sample Error?

Sample bias: when the sample recruited is made up of a particular type of person which may not reflect the target population.

Sample error: when a sample differs in qualities from the target population it intends to represent.

Define Random Sampling , and state its main strength and weakness

Definition: Defined as a sample in which every member of the population has an equal chance of being chosen

Strength: Free from researcher bias as they have no influence on who is selected.

Weakness: Difficult and time-consuming; may end up with an unrepresentative sample.

Define Opportunity Sampling, who usually uses it? and its main strength and weakness.

Definition: Taking people who are available at the time and fit the criteria (most used by psychology students)

Strength: Convenient as saves time and effort, also less costly.

Weakness: Biased (e.g., taken from only one street/town), so findings cannot be generalised

How is Stratified Sampling defined ? What are its strength and weakness?

Definition: Classifying the population into categories and choosing a sample from each category in the same proportions as they are in the population. (将总体分类，并按总体中的实际比例从各层中抽取样本。)

Strength: Avoids researcher bias and produces a representative sample. (避免研究者偏差，能产生代表性强的样本。)

Weakness: Time-consuming; strata cannot reflect all the ways people differ. (耗时；分层无法完全涵盖人与人之间的所有差异。)

Define Volunteer Sampling. What are its strength and weakness?

Definition: Participants become part of a study because they volunteer when asked or in response to an advert.

Strength: Easy, requires minimal input from researcher, less time-consuming.

Weakness: Volunteer bias (e.g., people being helpful or keen), which affects generalisability.

What does Target population mean in the context of sampling?

Definition: The entire group of people from which a sample may be drawn.

Context: Identifying everyone in the target population is the first step before applying methods like random sampling. (在应用随机抽样等方法前，第一步就是识别出目标总体中的所有人。)

Define Repeated Measures. What are its advantage and disadvantage?

Definition: All participants take part in all conditions of the experiment.

Advantage: Fewer people are needed as they take part in all conditions (i.e., saves time and money).

Disadvantage: There may be order effects (e.g., practice or fatigue effects).

Define Independent Groups. What are its advantage and disadvantage?

Definition: Participants are allocated to different groups where each group represents one experimental condition.

Advantage: Avoids order effects as people participate in one condition only.

Disadvantage: More people are needed (more time-consuming), and participant variables between groups may affect results.

Define Matched Pairs. What are its advantage and disadvantage?

Definition: Pairs of participants are first matched on some variable(s) that may affect the DV, then one assigned to condition A and the other to Condition B. (成对的参与者首先根据可能影响因变量的某些变量进行匹配，然后一人分配到条件A，另一人分配到条件B。)

Advantage: Reduces participant variables and avoids order effects (counterbalancing is not necessary).

Disadvantage: Very time-consuming trying to find closely matched pairs, and it is impossible to match people exactly.