总体（population）

• 定义：①具有某些共同的、可观测特征的一类事物的总体；②心理学研究中，指特定研究所关注的所有个体的集合。
• 基本单元：个体。
• 例子：想要统计北京市大学生的身高，那么总体就是北京市大学生。

• Definition：①The totality of a class of things with some common and observable characteristics. ②In psychological research, it refers to the set of all individuals that are the focus of a particular study.
• Basic unit：Individual.
• Example：If you want to count the heights of Beijing college students，the population is Beijing college students.

样本（sample）

• 定义：从总体中选出来作为真正研究对象的个体的集合。
• 特征：总体的子集。
• 诞生的原因：由于人力、财力的限制，难以统计到每一个人，只能从总体中抽取一些个体作为研究对象。
• 取样偏差：样本越大，越接近总体，对总体的代表性越强；样本小，可能造成取样偏差，对总体的代表性差。
• 取样的优点：①节约时间、开支；②抽样恰当的样本具有较强的代表性（怎样抽取样本才具有代表性？——随机取样）。
• 例子：想要统计北京市大学生的身高，可以在每个高校中随机取样一部分个体作为样本。

• Definition: The collection of individuals selected from the population as the research targets.
• Characteristic: The subset of population.
• Cause: Due to the limitation of human and financial resources, it is difficult to make statistics reach every individual. We have to select some individuals from the population as the object of study.
• Sampling bias: The larger the sample is, the closer it is to the population and the more representative it is of the population. Small sample may result in sampling bias and poor representation of the population.
• Advantages of sampling: ①Saving time and expenses. ②Properly sampled samples are highly representative.
• Examples: If you want to count the heights of college students in Beijing, a portion of individuals from each college can be taken as a sample by random sampling.

随机取样（random sampling）

• 定义：从总体抽取样本时，要求总体中每一个个体被抽到的机会均等。
• 用随机取样法得到的样本叫做随机样本。
• 具体方法：分层取样（按照年龄、性别比抽取）等。

• Definition: Each element of the population has an equal chance of been selected when drawing a sample from a population.
• The sample obtained by random sampling method is called random sample.
• Methods: Stratified sampling (by age, sex ratio), etc.