因果研究设计
Three Causal Conditions
 Concomitant variation ｘ和ｙ有同步变异 is the extent to which a
cause, X, and an effect, Y, occur together or vary together in the
way predicted by the hypothesis under consideration.
 The time order of occurrence condition states that the causing
event must occur either before or simultaneously with the effect; it
cannot occur afterwards.ｘ发生在ｙ前面
 The absence of other possible causal factors means that the factor
or variable being investigated should be the only possible causal
explanation.ｘ是ｙ的唯一或排他性原因
Figure 1a: Example of a Classic Scientific Experiment
Randomly sample 100 healthy
people during flu season.
Randomly Assign
50 get daily
vitamin C tablets
50 get daily
placebo tablets
Days later: Count # colds in each group
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EXTERNAL FACTORS IN CAUSAL RELATIONSHIPS
• History--Specific events external to an experiment, but occurring at
the same time, which may affect the criterion or response variable
(注意“历史“是指事件的影响)
• Maturation--Processes operating within the test units in an
experiment as a function of the passage of time per se (成熟是指实
验期间被试者的某些变化影响测量结果)
• Testing--Contaminating effect in an experiment due to the fact that
the process of experimentation itself affected the observed response
(测试效应可能影响因变量的测量结果)
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• Main testing effect--the impact of prior observation /treatment on
later observation (测试主效应指之前的测量影响后面的结果)
• Interactive testing effect--the condition when a prior measurement
affects the test unit’s response to the experimental variable (测试互
作效应指之前的测量和实验处理发生互作)
• Instrument Variation--Any and all changes in the measuring device
used in an experiment that might account for differences in two or
more measurements (工具变异指测量工具改变引起变化)
• Statistical Regression--Tendency of extreme cases of a
phenomenon to move toward a more central position during the
course of an experiment (统计回归指原来的极端值自动向平均
数靠拢的现象，和实验处理无关)
• Selection Bias--Contaminating influence in an experiment
occurring when there is no way of certifying that groups of test
units were equivalent at some prior time (选择偏差指事先存在的
组间差异，和处理无关)
• Experimental Mortality--Experimental condition in which test units
are lost during the course of an experiment (实验者流失)
内源和外源效度
内源效度: 效果确实是由原因引起的吗? (例如：我们能够肯定对手机
的选择完全受广告影响吗？)
外源效度: 我们可以把结果推广到群体中去吗? (例如我们能把实验
室结果推广到市场上去吗？)
Major Causal Designs
One-Shot Case Study 一次性案例研究
X
01
• There is no random assignment of test units.无随机配置
• Appropriate for exploratory, not for conclusive research
One-Group Pretest-Posttest Design 单组前试加后试设计
01 X 02
• A group of test units is measured twice.
• There is no control group.
• The treatment effect is computed as 02 – 01.
• The validity is questionable since extraneous variables are largely
uncontrolled.
Static Group Design 静态组间对比设计
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EG:
X 01
CG:
02
• A two-group experimental design.
• The experimental group 实验处理组(EG) is exposed to the
treatment, and the control group 对照组(CG) is not.
• Measurements on both groups are made only after the treatment.
• Test units are not assigned at random.
• The treatment effect would be measured as 01 - 02.
True Experimental Designs 真实或完全实验设计
EG: R 01 X 02
CG: R 03
04
• Test units are randomly assigned to either the experimental or the
control group.
• A pretreatment measure is taken on each group.
• The treatment effect (TE) is measured as: (02 - 01) - (04 - 03).
• Selection bias is eliminated by randomization.
• The other extraneous effects 外源效应 are controlled as follows:
02 – 01= TE 处理效应+ H 历史 + MA 成熟 + MT 测试主效 + IT
测试互作 + I 测量工具变异 + SR 统计回归 + MO 主体流失
04 – 03= H 历史+ MA 成熟+ MT 测试主效+ I 测量工具变异+ SR
统计回归+ MO 主体流失=EV(Extraneous Variables)
• The experimental result is obtained by:
(02 - 01) - (04 - 03) = TE + IT
• Interactive testing effect is not controlled
Posttest-Only Control Group Design 后试组间对照设计
EG : R
X
01
CG :
R
02
• The treatment effect is obtained by TE = 01 - 02
• Except for pre-measurement, the implementation of this design is
very similar to that of the pretest-posttest control group design
Time Series Design 时间序列设计
01 02 03 04 05
X 06
07 08 09 010
• There is no randomization of test units to treatments.
• The timing of treatment presentation, as well as which test units
are exposed to the treatment, may not be within the researcher's
control.
EG: 01 02 03 04 05
X
06 07 08 09 010
CG: 01 02 03 04 05
06
07 08 09 010
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• If the control group is carefully selected, this design can be an
improvement over the simple time series experiment.
• Can test the treatment effect twice: against the pretreatment
measurements in the experimental group and against the control
group.
Limits of Experiments (Time, cost and control)
• Experiments can be time consuming, particularly if the researcher
is interested in measuring the long-term effects.
• Experiments are often expensive. The requirements of
experimental group, control group, and multiple measurements
significantly add to the cost of research.
• Experiments can be difficult to administer. It may be impossible to
control for the effects of the extraneous variables, particularly in a
field environment.
• Competitors may deliberately contaminate the results of a field
experiment.
Summary of Designs
X
01
01
单次案例研究设计
X
02 单组前试加后试设计
X 01
EG:
02 静态组间对比设计
CG:
EG: R 01 X 02
CG: R 03
04 真实或完全实验设计
EG: R
X 01
CG: R
02 后试组间对照设计
01
02
EG: 01
CG: 01
03
02
02
04
03
03
05
04
04
X
05
05
06
X
07
06
06
08
07
07
09
08
08
010
09
09
010
010