A complete and coherent English summary of the lectures and workshops of Research Project (BT2103) in block . Includes some examples of the given slides.
LECTURE 2
Causal inference
Correlation does not imply causation. Several reasons why X and Y can correlate:
● X causes Y
● Y causes X
● Z causes both X and Y
● Spurious correlation
Reverse Causality: X appears to cause Y, but it is actually Y that causes Y
● → Sales of a brand of soda are higher during weeks of heavy advertising.
○ However, advertising is allocated when the stakes are greatest (e.g.,
during holidays and summer months). Thus, anticipated sales may
actually cause advertising.
Third Variable: X appears to cause Y, but both X and Y are actually caused by Z.
● On the average, the more toys a child has, the higher his or her IQ.
○ Both the number of toys and IQ may be caused by family resources such
as income (i.e., better nutrition and education).
When can we infer that X causes Y?
Three conditions for causality:
● Relationship between X and Y
○ X and Y vary together
● Time order
○ X cannot happen after Y
● Elimination of other possible causal factors
○ All other possible causes held constant or controlled
Experimental design
Independent variable is “manipulated” across groups or “between-subject”.
● Between-subject: one participant is assigned to one experimental condition of
the IV (e.g., ad A or ad B)
1
, ● Within-subject: one participant is assigned to several experimental conditions
(e.g., ad A and ad B)
Moderator
Experiments can also account for moderating variables, which affect the relationship
between the IV and the DV. The moderator can be either:
● Measured (e.g., with a Likert scale)
● Manipulated (e.g., with specific experimental conditions)
Experimental validity
Internal Validity
● Conclusions about the effects of IVs on DVs are valid
● How to ensure it? correct implementation of principles randomization, control of
extraneous factors, etc
● Lab studies are high in internal validity
External Validity
● Conclusions can be generalized outside the experiment e.g. lab participants →
consumers?
● Field studies are higher in external validity (although they tend to suffer from
internal validity)
Randomized Control Trial (RCT)
● In parallel groups: “between-subject experiment”
● In crossover: random allocation into different groups + DV measured several
times (e.g., before and after taking the drug).
● In cluster: pre-existing groups of participants (e.g., villages, schools) are randomly
selected to receive (or not receive) an intervention.
Designs that face threats to internal validity/causal claims
● Quasi-Experiment: Assignment to the experimental conditions is not random
(e.g., nutri-score in supermarket A vs. no nutri-score in supermarket B).
● Pre-post: The DV (e.g., stock price) is measured before and after an IV category
(e.g., before/after the new policy). Can be labeled a non-experimental
observational study.
WORKSHOP 1
Ensuring that all uncontrolled is random: A way to control for confounding factors
(“confounds”). Then you know that it’s actually X that causes your Y and not other
differences.
● Internal validity: A special case of “Holding everything the same”.
● External validity: Ensures that your effect holds under different conditions
2
Voordelen van het kopen van samenvattingen bij Stuvia op een rij:
Verzekerd van kwaliteit door reviews
Stuvia-klanten hebben meer dan 700.000 samenvattingen beoordeeld. Zo weet je zeker dat je de beste documenten koopt!
Snel en makkelijk kopen
Je betaalt supersnel en eenmalig met iDeal, creditcard of Stuvia-tegoed voor de samenvatting. Zonder lidmaatschap.
Focus op de essentie
Samenvattingen worden geschreven voor en door anderen. Daarom zijn de samenvattingen altijd betrouwbaar en actueel. Zo kom je snel tot de kern!
Veelgestelde vragen
Wat krijg ik als ik dit document koop?
Je krijgt een PDF, die direct beschikbaar is na je aankoop. Het gekochte document is altijd, overal en oneindig toegankelijk via je profiel.
Tevredenheidsgarantie: hoe werkt dat?
Onze tevredenheidsgarantie zorgt ervoor dat je altijd een studiedocument vindt dat goed bij je past. Je vult een formulier in en onze klantenservice regelt de rest.
Van wie koop ik deze samenvatting?
Stuvia is een marktplaats, je koop dit document dus niet van ons, maar van verkoper Milaa. Stuvia faciliteert de betaling aan de verkoper.
Zit ik meteen vast aan een abonnement?
Nee, je koopt alleen deze samenvatting voor €5,49. Je zit daarna nergens aan vast.
