490 likes | 561 Views
Chapter 10. http://members.aol.com/johnp71/javastat.html. Goal. Not only to be able to analyze your own data but to understand the literature that you read. Data Analysis. Statistics Parameter. Reporting your Results. With words…. With numbers…. With Charts/Graphs…. Data. Categorical
E N D
Chapter 10 http://members.aol.com/johnp71/javastat.html
Goal • Not only to be able to analyze your own data but to understand the literature that you read.
Data Analysis • Statistics • Parameter
Reporting your Results • With words…. • With numbers…. • With Charts/Graphs…
Data • Categorical • Quantitative
Quantitative • In this chapter: • Correlation • Frequency • distributions • Measures of Central Tendency • Mean • Variability • Standard deviation
Distributions • Skewed Distributions • Positive – scores trailing to the right with a majority at the lower end • Negative – scores trailing to the left
Distributions • Normal • Large majority of scores in the middle • Symmetrical • Bell-shaped • Mean, median, and mode are identical
Types of Curves... The Normal Curve:
Measures of Central Tendency • Mode • Median • Point at which 50% of scores fall above and below • Not necessarily one of the actual scores in the distribution • Most appropriate if you have skewed data
Measures of Central Tendency • Mean • Uses all scores in a distribution • Influenced by extreme scores • Mean = sum of scores divided by the number of scores
Variability • Range • Low to High • Quick and dirty estimate of variability • Standard Deviation
Standard Deviation • 1. Calculate the mean • 2. Subtract the mean from each score • 3. Square each of the scores • 4. Add up all the squares • 5. Divide by the total number of scores = variance • 6. Take the square root of the variance.
Standard Deviation • The more spread out the scores the larger the standard deviation. • If the distribution is normal then the mean + two standard deviations will encompass about 95% of the scores. (+ three SD = 99% of scores)
% of Scores in 1 SD 1 SD = 68% of sample
2 Standard deviations? 2 SD = 95% of sample
Group A 30 subjects Mean = 25 SD = 5 Median = 23 Mode = 24 Group B 30 subjects Mean = 25 SD = 10 Median = 18 Mode= 13 What can you tell me about these groups?
Use your text (p. 207-208) Check your scores with this link. Scores: 12, 10, 6, 15, 17, 20, 16, 11, 10, 16, 22, 17, 15, 8 Mean = ?? SD = ?? Calculate the Standard Deviation and Average
Excel • Now go to the following web page and click on “class data”: assignments • Calculate mean, median, mode, SD for the ACT and Writing column data.
Standard Scores • A method in which to compare scores • Z scores – expressed as deviation scores • Example: • Test 1= 80 • Test 2 = 75
Example • Test 1: mean = 85, SD = 5 • Test 2: mean = 65, SD = 10
Probability • We can think of the percentages associated with a normal curve as probabilities. • Stated in a decimal form. • If something occurs 80% of the time it has a probability of .80.
Example • We said that 34% of the scores (in a normal distribution) lie between the mean and 1SD. • Since 50% of the scores fall above the mean then about 16% of the scores lie above 1SD
Example • The probability of randomly selecting an individual who has a score at least 1SD above the mean? • P=.16 • Chances are 16 out of 100.
Example • Probability of selecting a person that is between the mean and –2SD?
Z-Scores • For any z score we know the probability • Appendix B
Z-Scores • Can also be calculated for non-normal distributions. • However, cannot get probabilities values if non-normal. • If have chosen a sample randomly many distributions do approximate a normal curve.
Determining Relationships Between Scores Correlation
Relationships • We can’t assign blame or cause & effect, rather how one variable influences another.
Correlation • Helpful to use scatterplots
Plotting the relationship between two variables Age = 11 Broad Jump = 5.0 feet Y axis Age 11 5.0 X axis 5 Feet
Plot some more (Age & Broad Jump) y Do you see a relationship?? Age x Feet
Outliers • Differ by large amounts from the other scores
Correlation…. • Is a mathematical technique for quantifying the amount of relationship between two variables • Karl Pearson developed a formula known as “Pearson product-moment correlation”
Correlation • Show direction (of relationship) • Show strength (of relationship) • Range of values is 0 - 1.0 (strength) • 0 = no relationship • 1 = perfect relationship • Values may be + or - (direction)
Correlation r= 1.0 r = 0 r = -1.0
Correlation Strength • Very Strong .90 - 1.0 • Strong .80 - .89 • Moderate .50 - .79 • Weak < .50
Types of relationships Curvalinear Sigmoidal Linear
Test Your Skill Guess the Correlation
Quick Assignment • For the same excel spreadsheet that we opened earlier calculate a correlation coefficient for the ACT vs. Tricep. • Make a scatterplot of tricep vs. ACT. • Scatterplot and correlation for ACT vs. Writing
Coefficient of Determination • Determines the amount of variability in a measure that is influenced by another measure • I.e. how much does the broad jump vary due to varied ages? • Calculated as r2 (Corr. Squared)
Example: • Say that strength and 40yard sprint time have an r = .60 • How much does a variation in strength contribute to the variation in sprint speed?
Summarizing Data • Frequency Table • Bar Graphs/Pie Charts • Crossbreak Table • A graphic way to report a relationship between two or more categorical variables.
Assignment • Under assignments on my web page there is an excel spreadsheet published entitled “assignment 1”. • Download the spreadsheet by clicking here assignments
Assignment • 1. Calculate the mean, mode, and median for body density, ACT Score, and Reading Score on sheet 1 • 2. Calculate the mean and SD for TC, Trig, HDL, and LDL on sheet 2
Assignment • 3. Calculate a correlation coefficient for body density and age, ACT and Reading Scores, TC and LDL, and Trig and HDL • 4. Make a scatterplot for HDL and Trig as well as LDL and Total
Assignment • 5. Make a bar graph for the mean Total, Trig, LDL, HDL values.