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Lecture 2

Department

PsychologyCourse Code

PSYB07H3Professor

Dwayne PareLecture

2This

**preview**shows pages 1-2. to view the full**8 pages of the document.**PSYB07 - Data Analysis in Psychology

Lecture 2 - Descriptive Statistics

Readings: Chapter 2

Lecture Outline

● Descriptive Statistics vs. Inferential Statistics

○ DS can be something that describes data from a sample/population

○IN is used to try to infer from the sample data what the population might

think

● Distribution

● Central Tendency

Distribution

● Modality

○ How many peaks does the distribution have?

○ Mode -> peak of the distribution

○ Modality -> # of peaks

○ Unimodal

■ Distribution with one clear peak or

most frequent value. The values

increase at first, rising to a single

peak where they then decrease. The

“mode” in unimodal refers to the

local maximum in a chart

○ Bimodal

■ A continuous probability distribution

with two different modes. These

appear as distinct peaks (local

maxima) in the probability density

function

○ Multimodal

■ Distribution that has multiple modes

(thus two or more “peaks”).

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○ Amodal (uniform)

○

● Symmetry

○ Is the distribution the same on both sides?

○ Skewness

■ Symmetrical vs. Asymmetrical

■ An asymmetrical distribution is skewed

● The body of the data is shifted to one side

● One of the tails is longer than the other

●

■ The direction of skew is the direction that the tail is pointing

■ Positively skewed

■

● Lots of the body is on the negative side

● E.g., when students do poorly in the class

■ Negatively Skewed

■

● Lots of the body is on the positive side

● E.g., when students do really well in the class

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● Kurtosis

○ How pointy or flat is the distribution?

○ Kurtosis - how pointy or flat the shape of the distribution is

■ Where is the data clustered?

○ Need to know because it changes the analysis we need to use

○ Mesokurtic

■ Normal distribution

○

○ Platykurtic

○

○ Leptokurtic

○

● Normal Distribution/Bell Curve

○ Single peak

○ Symmetrical

● The graph is telling us in respect to marks is that there is a little bit of people who did

really well (right side), a little bit of people who didn’t do so well (left side) and in the

middle is people who did averagely

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