# 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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