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Causal relationship requires: 


	Temporal order. 

	Alternative causes. 

	Causal Mechanism. 

Spurious relationship: a relationship between two variables that is produced by their joint dependence on a prior variable. 

If the relationship is in one group, it is “conditional upon [variable]”. 

Partially spurious if the relationship is weakened. 

Need to understand a three way table. Three way tables are to show that two variables influence something. Formed the same way as controlling. 

Intervening variable: A variable that comes between a cause and effect. Use “because”. The variable needs to relate to both. 

Focus groups don’t represent the population or random sampling. 

Probability samples are for stratified and cluster samples. 

Margin of error are not for small samples or mall intercept.