PS102 Lecture Notes - Lecture 3: Statistical Inference, Descriptive Statistics, Developmental Psychology
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How do psychologists make sense of research results?
(Lecture 2 Continued)
● Experiments allow causal conclusions
○ Uses inferential statistics to make inferences about data sets
■ Conclude differences between groups are genuine and not due to chance
■ First, need to look at Descriptive statistics
○ Descriptive statistics= statistics that are used to organize raw data into
meaningful descriptions
■ Measures of central tendency= a numerical value that represents the
center of the distribution
● Example: mean, median, mode
■ Measures of variability= a numerical value that represents how different
the scores within a group are from each other
● Example: range, standard deviation, variance
○ Descriptive statistics in our example:
■ Recall we were comparing Grade 12 math scores in people who received
a minimum of 10 hours a week of musical training from 3-13 years of age
with people who had no musical training
Using the appropriate inferential test, a researcher calculates the statistical significance of
their results.
➢ When you have a ‘very low probability’ that your findings are due to chance
○ What is considered a ‘very low’ probability?
■ Researchers generally accept a 5% chance that the results are due to
chance alone
● The calculation of this is based on whether the difference between
groups is greater than the differences within a group
● If so, one would say that “p < .05”
What is the appropriate inferential test? It depends on your research design
➢ Recall our example: compared two groups of participants tested at one point in time and
manipulated one independent variable
○ The inferential statistic used for testing the statistical significance of two groups is
a t-test
■ If the difference between the two means is great enough, and the
variability within groups is small enough, then the t-value will be big
■ Big t-value= Small p-value
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Chapter 4 Overview
● Issues in developmental psychology
● Studying developmental psychology
● Prenatal development
● Infancy and childhood
● Adolescence
● Adulthood
Issues in developmental psychology
● Development:
○ Refers to the continuities and changes that occur within the individual between
conception and death
○ The most dramatic changes occur early in the lifespan, so we will focus there
➔ Nature and nurture
◆ How do our genes and experience guide development over our lifespan?
➔ Change and stability
◆ In what ways do we change as we age, and in what ways do we stay the same?
➔ Sensitive period
◆ How much flexibility do we have in the timing of our exposure to specific
environmental input in order for a specific ability to develop ‘normally’?
➔ Continuity versus stages
◆ Is development a gradual change or are there some leaps to a new way of
thinking or behaving?
● Longitudinal design:
○ A developmental research design in which the same individuals are studied
repeatedly over some subset of their lifespan
○ Example: Birth year is 1925 (see table)
○ Advantages:
■ Can access developmental change!
○ Disadvantages:
■ Very expensive and time consuming
■ Selective attribution:
● Loss of people such that the sample ends up being completely
different from the population as a whole
■ Original research question may become obsolete
■ Practice effects
■ Cohort effects (Generational)
1930
1950
1975
2000
5 years
25 years
50 years
75 years
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