📚 Experimental Methods and Variable Control in Psychology | 心理学实验方法与变量控制
Psychology is the scientific study of behaviour and mental processes. At the heart of this science lies the experiment, a method that allows researchers to establish cause-and-effect relationships by manipulating variables under controlled conditions. This article explains the experimental method and variable control — essential exam topics in psychology.
心理学是对行为与心理过程的科学研究。这一学科的核心是实验法——研究者通过在受控条件下操纵变量，从而建立因果关系。本文围绕实验方法与变量控制展开，这是心理学考试中的核心考点。
1. What Is an Experiment? | 什么是实验？
An experiment is a research method in which the researcher deliberately manipulates one variable (the independent variable) and measures its effect on another variable (the dependent variable), while holding all other conditions constant. The aim is to establish cause and effect: change in the independent variable causes change in the dependent variable.
实验是一种研究方法：研究者有目的地操纵一个变量（自变量），并测量它对另一个变量（因变量）的影响，同时保持其他条件不变。实验的目的是建立因果关系——自变量的变化引起因变量的变化。
Unlike correlational studies, which only describe relationships, experiments can test causal hypotheses. This is why experiments are considered the “gold standard” in psychological research.
与只能描述关系的相关研究不同，实验能够检验因果假设。因此，实验被视为心理学研究中的”金标准”。
2. Types of Experiments | 实验的类型
Laboratory experiments are conducted in a controlled environment. The researcher controls the IV, the DV and the extraneous variables as much as possible. This gives high internal validity, but the artificial setting may make behaviour less natural, lowering external validity and ecological validity.
实验室实验在受控环境中进行。研究者尽可能控制自变量、因变量和额外变量。这带来较高的内部效度，但人为环境可能使行为不够自然，从而降低外部效度和生态效度。
Field experiments take place in participants’ real-world environments, such as a school or a street. The researcher still manipulates the IV, but participants are usually unaware they are in a study. This increases external validity, but there is less control over extraneous variables, and ethical issues such as lack of informed consent can arise.
现场实验在参与者的真实环境中进行，例如学校或街道。研究者仍然操纵自变量，但参与者通常不知道自己正在参与研究。这提高了外部效度，但对额外变量的控制较弱，也可能引发缺乏知情同意等伦理问题。
Natural experiments (or quasi-experiments) occur when the IV is not manipulated by the researcher but arises naturally, for example comparing children who were adopted with those who stayed in orphanages. These allow research on variables that are unethical or impossible to manipulate, but they cannot establish causation as firmly as true experiments because there is no random allocation.
自然实验（又称准实验）是指自变量并非由研究者操纵，而是自然发生的情况，例如比较被收养的儿童与留在孤儿院的儿童。自然实验可用于研究那些在伦理上不允许、或无法操纵的变量，但由于没有随机分配，它无法像真正的实验那样牢固地建立因果关系。
3. Independent Variable (IV) and Dependent Variable (DV) | 自变量与因变量
The independent variable (IV) is the factor that the experimenter manipulates or changes. It is the presumed cause in the study. The dependent variable (DV) is the factor that is measured; it is the presumed effect. For example, in a memory experiment, if researchers give one group caffeine and another group a placebo, the amount of caffeine is the IV and the number of words recalled is the DV.
自变量（IV）是实验者操纵或改变的因素，是研究中预设的原因；因变量（DV）是被测量的因素，是预设的结果。例如，在记忆实验中，如果研究者给一组参与者服用咖啡因、给另一组服用安慰剂，那么咖啡因的剂量就是自变量，回忆出的单词数量就是因变量。
Every experiment must have at least one IV and one DV. The IV must have two or more levels or conditions, so that the researcher can compare the effects of different values of the IV on the DV.
每个实验至少包含一个自变量和一个因变量。自变量必须有两个或多个水平（条件），研究者才能比较自变量的不同水平对因变量的影响。
4. Operational Definitions | 操作性定义
An operational definition specifies exactly how a variable is measured or manipulated in a study. For example, “aggression” might be operationally defined as “the number of times a participant presses a button to deliver a loud noise to another participant.”
操作性定义明确规定了变量在研究中如何被测量或操纵。例如，”攻击性”可以被操作性地定义为”参与者按下按钮向另一名参与者传送响亮噪音的次数”。
Operational definitions make research replicable. Without them, two researchers might measure the same concept in different ways and obtain inconsistent results. In exams, students are often asked to suggest an operational definition for the IV or DV.
操作性定义使研究可以被重复验证。没有它们，两位研究者可能用不同方式测量同一概念，得到不一致的结果。考试中常要求学生为自变量或因变量提出操作性定义。
IV (caffeine) → DV (recall score) | 自变量（咖啡因）→ 因变量（回忆得分）
5. Extraneous Variables and Confounding Variables | 额外变量与混淆变量
Extraneous variables (EVs) are any variables other than the IV that could affect the DV. For example, in a memory test, noise level, time of day, participant age and gender are all potential extraneous variables.
额外变量（EV）是除自变量以外、可能影响因变量的任何变量。例如，在记忆测试中，噪音水平、一天中的时间、参与者的年龄和性别都是潜在的额外变量。
A confounding variable (CV) is a special type of extraneous variable that systematically varies with the IV, making it impossible to tell which variable caused the change in the DV. For example, if all participants in the caffeine group are tested in the morning and all participants in the placebo group are tested in the afternoon, time of day is a confounding variable because it changes together with the IV.
混淆变量（CV）是一种特殊的额外变量，它随自变量系统地变化，使人们无法判断究竟是哪个变量引起了因变量的变化。例如，如果咖啡因组的参与者全部在上午测试，安慰剂组的参与者全部在下午测试，那么时间就是混淆变量，因为它与自变量一同变化。
The key difference: extraneous variables are merely unwanted; confounding variables are dangerous because they offer an alternative explanation for the results.
关键区别在于：额外变量只是”不受欢迎”，而混淆变量则很危险，因为它为实验结果提供了另一种可能的解释。
6. Types of Experimental Design | 实验设计的类型
There are three main experimental designs used to control participant variables.
控制参与者变量主要有三种实验设计。
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Independent groups design: different participants take part in each condition. It avoids order effects and demand characteristics are less obvious, but participant differences may become a confounding variable.
独立组设计：每个条件使用不同的参与者。它可以避免顺序效应，需求特征也不太明显，但参与者差异可能成为混淆变量。
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Repeated measures design: the same participants take part in all conditions. It eliminates participant variables and requires fewer participants, but introduces order effects such as practice and fatigue.
重复测量设计：同一批参与者参加所有条件。它消除了参与者变量，需要的参与者更少，但会引入练习效应和疲劳效应等顺序效应。
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Matched pairs design: different but similar participants are paired on key variables such as age and IQ, and one member of each pair is assigned to each condition. It balances participant variables while avoiding order effects, but matching is difficult and time-consuming.
匹配组设计：将不同但相似的参与者按关键变量（如年龄和智商）配对，每对中的一人分入各个条件。它平衡了参与者变量，又避免了顺序效应，但匹配过程困难且耗时。
| Design | 设计 | Strength | 优点 | Weakness | 缺点 |
| Independent groups | 独立组 |
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