Statistics

1
Statistics

• Sample Descriptive Statistics
• Population Inferential Statistics

2
Descriptive Statistics

• Measures of central tendency
• Mean
• Median
• Mode
• Measures of variability
• Standard deviation (SD)
• Variance (SD squared)
• Correlation measure of relatedness

3
Populations and Samples

• Population all the possible scores
• All living humans
• All possible rolls of a pair of dice
• Sample a subset of the population
• Random sample best kind unbiased
• Relationship of sample mean to population mean
  example number of pets

4
Example of Comparing 2 Means

• DV of minutes balancing on one foot
• IV whether blindfolded or not
• Hypothesis Lack of visual cues decreases balance
• Means of two samples 2.6 yes, 5.1 no
• Confirmed hypothesis?
• Is the difference due to chance?
• How can you tell if a difference found in an
  experiment is due to chance?
• How often do differences this big occur by
  chance?

5
Tests of Significance

• t
• F
• Tell us how often we would get the results we see
  in our sample just by chance

6
Hypothesis Testing

• H0 the null hypotheis
• Mean1 Mean2
• Experimental Condition Control Condition
• H1 the research hypothesis
• Mean1 does not equal Mean2
• Experimental Condition does not equal Control
  Condition

7
Hypothesis Testing Logic

• Assume H0
• Calculate a test statistic (such as t) to get p
  (p how often a difference this large would
  occur by chance)
• If p lt .05, conclude that H0 is false (reject
  H0)
• If you reject H0, you are left with H1
• Conclude that the means are really different
• Say the difference is statistically
  significant.
• If p gt .05, you can not reject H0
• Say the difference was not statistically
  significant.

8
Testing Hypotheses

• Are the means for the two groups really
  different? (Blindfolded vs. not)
• Steps to Follow
• Check for invalid data (analyze-gt descriptive
  statistics -gt explore)
• Check for outliers remove outliers
• Compare means with t-test (analyze -gt compare
  means)
• Independent Samples for 2 groups
• Paired Samples for repeated measures (one
  group)