Why is this important? Requirement Understand research articles Do research for yourself Real world

The Three Goals of this Course 1) Teach “factoids” 2) Teach a new way of thinking 3) Self-Confidence in statistics

Statistics

Descriptive Statistics

Practice Based on a sample of participants, it appears that a new drug will be effective at stopping headaches The enrollment in this course as of December 15th was 22

Practice On your first test you received a score of 84 out of 100 Markey will likely be the next president; of the 100 people surveyed 82% said they would vote for him

Inferential Statistics Problem: Is that going to be the exact answer? Chance influences the sample –“true” variation –“error” variation Sample = “true” + “error”

The meaning of numbers 90 The number correct on a test out of 100 The last two digits of your SSN Your place in a race with 100 participants Your place in the Boston Marathon The percentile you scored on the GRE

Nominal Scale Are not really scales at all They do not scale items along any dimension, but rather label them Numbers are used as names and have no quantitative value

Nominal Scales Gender Political party Your SSN Religion

Ordinal Scales Has the characteristics of the nominal scale PLUS: the characteristic of indicating greater than or less than –i.e., RANK ORDER

Ordinal Scales Rank of professor Your place in a foot race Saying “This class is smaller then my other class”

Interval Scales Has the properties of BOTH the nominal and ordinal scales PLUS: the intervals between the numbers are equal –e.g., the distance between 4 and 5 is the same distance between 1 and 2

Interval Scales Temperature –the difference between 10 o F and 20 o F is the same as the difference between 80 o F and 90 o F Problem: What does 0 o F mean? With interval scales you CAN NOT make ratio statements

Interval Scale Appears twice as large

Interval Scale Now it appears three-times as large!

Ratio Scales Has all the characteristics of the nominal, ordinal, and intervals scales PLUS: it has a true zero point This zero point indicates a complete absence of the thing measured

Ratio Weight Height Speed Distance

Features of the four scales

Why are the types of scales important? They help you understand what type of statistic to use

Practice Inches on a yardstick Drivers licenses number Dollars as a measure of income Order of finish in a car race Intelligence test scores

1) Is depressed, blue 2) Is not relaxed, does not handle stress well 3) Can be tense

4) Worries a lot 5) Is easily upset

Neuroticism Raw Score Add your answers –Your score can range between What does your score mean? Note: It is meaningless unless you know how others scored

Simple Frequency Distribution 1) Find the highest and lowest scores 2) Write in descending order all the numbers from 24 to 6

Simple Frequency Distribution 3) Start with the number in the upper-left corner, draw a line under it, and place a tally mark in the frequency distribution 4) Do this with all the data 5) Count the number a tally marks

Group Frequency Distribution Scores are grouped into equal-sized ranges called “class intervals” Usually want around 10 class intervals

Dieting

Pornography

Prostitution

Mate Seeking

Graphic Presentation of Data Basic parts of a graph X axis Y axis

Histogram Graphs quantitative data Neuroticism data

Graphing Data Frequency distributions give exact values, but lack a visual summary of the data Histographs provide a visual summary of the data, but lack exact values

Stem-and-Leaf Display Provide both exact values and a visual summary of data

Stem-and-Leaf Separate each value into a “stem” and a “leaf” Since we are using two digit numbers, the tens digit is the stem and the units digit is the leaf StemLeaf 12 The number 12

Stem-and-Leaf Display Group the numbers with the same stems and list the stems in numerical order. (If your leaf values are not in increasing order, order them now.) StemLeaf

Stem-and-Leaf Display Stem-and-leaf display with a bigger data set Note: The stem-and-leaf is like a histogram turned sideways!

Histogram

Frequency Polygon

Describing Distributions Bell-shaped distribution

Describing Distributions

Kurtosis The relative concentration of scores in the center of the distribution Mesokurtic

Kurtosis The relative concentration of scores in the center of the distribution Platykurtic

Kurtosis The relative concentration of scores in the center of the distribution Leptokurtic

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