Correlation, Causation, Experiments, and the Scientific Method

Correlation vs. Causation

  • A correlation coefficient indicates the strength of a correlation.

  • Correlation never implies causation, irrespective of its strength.

Positive and Negative Correlation

  • Negative correlation: one variable increases as the other decreases.

  • Positive correlation: both variables increase together.

  • Correlation coefficients range between -1 and +1.

  • Values of +0.85 or +0.9 indicate strong correlations.

Correlation Examples

  • The correlation doesn't equal causation.

  • Spurious correlations:

    • Facebook introduction and cholesterol decline after Justin Bieber's birth.

    • Number of math doctorates and suicides (positive correlation of 0.86).

Establishing Causation

  • Experiments are necessary to determine cause-and-effect relationships.

  • Experiments require regulated procedures and defined operational definitions for replication.

  • Independent Variable (IV):

    • The variable that is manipulated.

  • Dependent Variable (DV):

    • The variable that is measured depends on the IV.

  • Example: Aspirin's effect on headache symptoms

    • IV: Aspirin

    • DV: Headache symptoms

Random Assignment and Experimental Groups

  • Random assignment reduces pre-existing differences between groups.

  • Avoid hand-selecting group members unless sex/race/age is deliberately tested.

  • Experimental group:

    • Experiences the manipulation (receives the IV; e.g., aspirin).

  • Control group:

    • Serves as a baseline for comparison.

    • Receives a placebo (e.g., sugar pill) to control for the placebo effect.

  • Placebo effect: participants show improvement because they believe they are receiving treatment.

  • If the placebo reduces symptoms, the actual treatment's effectiveness may be questionable.

Research Ethics

  • Research participants have rights, which are increasingly important.

  • IRB (Institutional Review Board) approval is necessary for research.

  • Informed consent:

    • Includes explaining the study, potential risks, and benefits.

    • Participants can revoke consent at any time.

  • Confidentiality:

  • Debriefing:

    • Going over the experiment afterward.

  • Deception:

    • Rare; only used if absolutely necessary.

Cognitive Biases

  • Hindsight bias (the "I knew it all along" effect):

    • Believing one should have seen the signs after an event has occurred.

    • Example: recognizing signs of infidelity after it's discovered.

  • Confirmation bias:

    • Seeking information to support existing beliefs leads to a biased approach.

    • Need to look for refuting stuff and explain why one's position is still better.

  • “Man Who” bias: the statistical exception argument. Something didn’t work for one person, but somebody knows “a man who” it did work for

Neuron Structure and Function

  • Neuron (nerve cell): essential for transmitting information.

  • Three functions: receiving, interpreting, and transmitting information.

  • Information travels in one direction: dendrites → soma → axon → terminal buttons.

  • Dendrites:

    • Receive signals (like fingers).

  • Soma:

    • The cell body interprets information.

  • Axon:

    • Transmits the signal down the neuron to the terminal buttons.

  • Terminal buttons:

    • Release neurotransmitters to pass the signal to the next neuron.

  • Myelin sheath:

    • The fatty substance of the axon.

    • Speeds up neurotransmission.

The Synapse, Communication Between Neurons, and Enzymes

  • Synapse: space between neurons.

  • Presynaptic neuron (terminal button) and postsynaptic neuron (dendrite).

  • Connections between neurons form memory pathways.

  • Each neuron transmits information through neurotransmitters released into the synapse.

  • Neurotransmitters fit into receptors on the dendrites of the next neuron to relay the signal.

  • Enzymes: destroy neurotransmitters that don’t go the right way.

  • Keep things in line with what is supposed to do, like the security. Make sure what goes in here should go in here.

Neurotransmitters

  • Key information carriers are necessary for body function.

  • Examples include hunger, digestion, and walking.

  • Dopamine

    • Voluntary movement, learning, memory, emotion, thinking, pleasure, or rewardWee release dopamine with every thought

    • Dopamine is absorbed during sleep, which is called reuptake

    • Too much? schizophrenia

    • Not enough? Parkinsons disease

  • Serotonin

    • Necessary for mood regulation

    • Too much serotonin has no effect.

    • Not enough? Anxiety and depression

    • Reuptake vs. SSRIs

  • Acetylcholine

    • Muscle action

    • Not enough: can result in paralysis.

    • Too much- the action is tremors.

  • ## Norepinephrine

    • Internal Caffeine: wakes the body up and triggers our fight or flight response

    • Not enough? fatigue

    • Too much can be fatal: heart attacks.

  • GABA (Gamma-aminobutyric acid)

    is necessary to calm us down. It terminates the fight-or-flight response.

    Too much? no effect

    Not enough? Panic attacks, seizures, tremors, insomnia

  • Endorphin- “runner’s high” our internal morphine

    Reduces pain and elevates feelings of pleasure