# PS102 Lecture Notes - Lecture 3: Statistical Inference, Descriptive Statistics, Developmental Psychology

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Published on 20 Jan 2018
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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
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:
repeatedly over some subset of their lifespan
Example: Birth year is 1925 (see table)
Can access developmental change!
Very expensive and time consuming
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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