# PSYC 102 Lecture Notes - Descriptive Statistics, Central Tendency, Randomized Controlled Trial

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25 Jan 2013
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Psychology 102: Developmental, Social, Personality, and Clinical Psychology
Lecture #3 - January 10, 2013
Replication: same finding with different participants in different situations
Random sampling: when each member of the target population has an equal chance of
inclusion in a sample (unbiased sample)
Three Basic Types of Scientific Studies
Descriptive: careful and accurate description (questionnaires and interviews)
o Naturalistic observation (observing life as it happens)
o Case studies (observe just a subset or a small group)
Correlational: evaluating relationships (links between two things, or among several things)
o Amount of sleep and the correlation to depression
o Can range from 0.00 to 1.00
No relationship 0.00, perfect relationship (1.00/-1.00)
Sign (+/-) indicates the direction of relationship (positive/negative)
Experimental: exploring cause and effect
o We will control one of the variables to see how the other variable reacts
Does the variable effect the outcome (amount of sleep and depression)
Depends on what is the independent and dependent variable
Independent variable: a factor manipulated by the experimenter
o The effect of the independent variable is the focus of the study
Dependent variable: a factor that may change in response to an independent variable
Evaluating Therapies:
Experimental condition: exposes the participant to the treatment
Control condition: participant is not exposed to the treatment
Placebo: an inert substance or condition that takes the place of an active treatment agent
Evaluating therapies: random assignment of participants to experimental or control
conditions
o Minimize all other differences between the groups except the treatment
Double-Blind randomized controlled trial: research participants and the researcher are
unaware of each participant's status (treatment or placebo)
Statistics:
Statistical procedures analyze and interpret data allowing us to see what the unaided eye
misses (objective and convenient)
Descriptive statistics: a meaningful description of data is important in research
o Misrepresentation may lead to incorrect conclusions
Purpose of Statistical Data:
Central tendency: something represents the general scores
Variation: something that represents the variation of scores
Mode: the most frequent occurring score in distribution
Mean: the middle of all scores (add up all, and divide by the quantity)
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