# 13. Statistics, Tests and Measurements (Ch2)

### 13.1 Descriptive and Inferential Statistics Samples, populations, norms

• Statistics
• collection, analysis, interpretation, and presentation of numeric data
• Samples
• representative subset of larger population
• random sample
• Populations
• group of people looking to study
• Norms
• identifying normal behavior of group to compare to
• standardizing
• Descriptive Statistics
• used for correlational and experimental designs
• measurements of behavior from sample
• Mean
• average
• Mode
• most commonly occurring score
• Median
• middle score, separates lower and upper halves of scores
• Standard Deviation
• statistical measure of how much scores in a sample vary around the mean
• higher SD = more variability (more spread)
• lower SD = less variability (less spread)
• Normal Distribution
• bell curve showing symmetrical alignment of two variables (e.g Intelligence)
• Inferential Statistics
• inferences about population based on characteristics of sample
• statistical significance
• not likely to have happened by chance
• significant equals 5% of the time or less

### 13.2 Reliability and Validity • Reliability

• stability and consistency of scores
• does not need to be valid to be reliable
• Types of Reliability

• test-retest reliability • internal consistency
• How well does a test correlate with itself
• split-half reliability
• Cronbach’s alpha: avg correlation for every way a test can be split in half • Validity

• how well a test measures what it is supposed to measure
• must be reliable to be valid
• Types of validity

• face/content validity
• whether a test looks as though it is measuring what it is supposed to measure
• predictive validity
• how well scores on the test predict the actual behavior of the type that the test is supposed to measure
• construct validity
• whether the scores on a questionnaire are related in expected ways, either positively or negatively, to scores on other questionnaires that are proposing to measure the same thing. • standardizing measures

### 13.3 Types of Tests

• Tests used to rule out chance
• t-test: computed for two means to see if they come from same population (e.g., of two groups or variables)
• ANOVA: analysis of variance • Pearson correlation coefficient (-1.0 to +1.0) ### 13.4 Measurement of Intelligence

• Stanford-Binet Intelligence Scale

• first IQ test
• still widely used today
• norming and standardization
• Wechsler Intelligence Tests

• WISC-V: Children
• WPPSI-IV: Pre-school and primary school • Flynn effect

• each generation, higher IQ ### Quiz

• Which of the following is a measure of central tendency that can be easily distorted by unusually high or low scores?
• (A) Mean
• (B) Mode
• (C) Median
• (D) Range
• (E) Standard deviation
• Which of the following statistics indicates the distribution with the greatest variability?
• A variance of 30.6
• (B) A standard deviation of 11.2
• (C) A range of 6
• (D) A mean of 61.5
• (E) A median of 38
• Which of the following is a true statement about the relationship between test validity and test reliability?
• (A) A test can be reliable without being valid.
• (B) A test that has high content validity will have high reliability.
• (C) A test that has low content validity will have low reliability.
• (D) The higher the test’s validity, the lower its reliability will be.
• (E) The validity of a test always exceeds its reliability.
• If the null hypothesis is rejected, a researcher can conclude that the
• (A) treatment effect was significant
• (B) theory must be modified, a new hypothesis formed, and the experimental procedure revised
• (C) theory does not need modification, but the hypothesis and the experimental procedure need revision
• (D) theory and hypothesis do not need modification, but the experimental procedure needs revision
• (E) hypothesis is false
• In order to illustrate how often a particular score occurs in a given data set, researchers use
• (A) inferential techniques
• (B) cognitive mapping
• (C) cluster analysis
• (D) the median
• (E) a frequency distribution