Unit 3: Science of Psychology WHS AP Psychology Unit 3: Science of Psychology Essential Task 3-6: Apply basic statistical concepts to explain research findings: - Descriptive Statistics: Central Tendency  (mean, median, mode, skewed distributions) Variance ( range, standard deviation, and normal distributions) Logo Green is R=8 G=138 B=76 Blue is R= 0 G=110 B=184 Border Grey is R=74 G=69 B=64

The Science of Psychology Approaches to Psych Growth of Psych Research Methods Statistics Descriptive Correlation Experiment Case Study Survey Naturalistic Observation Inferential Ethics Sampling Central Tendency Variance Careers We are here

Essential Task 3-6: Descriptive Statistics: Central Tendency Variance Outline Descriptive Statistics: Central Tendency  Mean, median, and mode skewed distributions Variance  Range standard deviation normal distributions

Statistical Reasoning Statistical procedures analyze and interpret data and let us see what the unaided eye misses. OBJECTIVE 15| Explain the importance of statistical principles, and give an example of their use in daily life. Composition of ethnicity in urban locales 4

Central Tendency Tendency of scores to congregate around some middle variable A measure of central tendency identifies what is average or typical in a data set 5

Measures of Central Tendency Mode: The most frequently occurring score in a distribution. Mean: The arithmetic average of scores in a distribution obtained by adding the scores and then dividing by their number. Median: The middle score in a rank-ordered distribution. OBJECTIVE 17| Describe three measures of central tendency and tell which is most affected by extreme scores. 6

But the mean doesn’t work in a skewed distribution The Median is a much better measure of the center 7

Skewed distributions Negatively Skewed Positively Skewed 8

Measures of Variation Statistical dispersion (how distributed the data points are) is a key concept in statistics. Two key ways of measuring statistical dispersion Range Standard Deviation 9

Range The range simply gives the lowest and highest values of a data set. 10

Standard Deviation Standard deviation gives a measure of dispersion. Essentially, they are measures of the average difference between the values. Standard deviation gives a value that is directly comparable to your mean values. 11

Formulas for Standard Deviation

Standard Deviation 13

Standard Deviation in Action A couple needs to be within one standard deviation of each other in intelligence (10 points in either direction). —Neil Clark Warren, founder of eHarmony.com 14

Normal Distributions The distribution of data also gives us key info. We know that many human attributes… e.g height, weight, task skill, reaction time, anxiousness, personality characteristics, attitudes etc. …follow a normal distribution. 15

Normal Distribution 16

IQ follows a Normal Distribution Mean = 100 SD = 15 17

What percentage score below 100? Mean = 100 SD = 15 18

What percentage score below 100? Mean = 100 SD = 15 19

What percentage score above 100? Mean = 100 SD = 15 34.1% + 13.6% + 2.1% 20

Normal Distribution 21

What percentage score between 85 and 100? Mean = 100 SD = 15 34.1% 22

Normal Distribution 23

What percentage score between 85 and 115? 34.1% + 34.1% = 68.2% Mean = 100 SD = 15 24

What percentage score between 70 and 130? Mean = 100 SD = 15 13.6% + 34.1% + 34.1% + 13.6% = 95.4% 25

What percentage score below 70 and above 130? Mean = 100 SD = 15 26

Interpret this graph Figure 6. The distribution of IQ scores in male and female populations. Adjusted parameter values yielded a male-female gap of 0.162 SD in g equivalent to 2.43 IQ points in favor of men 27