Chapter 2 & Appendix B: Statistics
Monday, September 26, 20112:00 PM
Statistics: What It's About
- The use of numbers
- Statistical methods allow for the collection, classification
- Statistics are just another way to quantify (assign numbers to) properties of objects or events of interest
- The use of numbers increase precision of communication/description
- Statistical methods are used to go beyond the numbers
○ Extracting info and permitting accurate interpretations
Populations &Samples
- Population-- all members of a group who are alike on at least one specific characteristic
- Sample-- any number of cases less than the total number of cases in the population from which it is drawn
- Samples are usually the object of studies
- Info about samples is used to make inferences about the characteristics of the larger population as a whole
- Samples must be representative of the population in order to draw meaningful and accurate inferences
- Samples from different populations can be compared in a study (e.g., autistic children vs. normally
developing children)
- Samples must be comparative
- Sample selection methods matter
Types of Samples
- Random sample-- each member of the pool has an equal probability of being selected on any given draw
and each possible sample of members has an equal probability of being selected
- Randomized sample-- each member of the sample has an equal chance of being assigned to a given
condition of the experiment
- Matched sample-- yields pairs of observations to produce highly comparable groups
○ Two participants are paired based on similarities in relevant characteristics and each takes part in one
of the conditions, OR
○ The same participant takes part in both conditions
○ Most suitable for experiments in which there are only 2 conditions or groups
Parametersand Statistics
- Population parameters-- the properties of populations (e.g., λ)
○ E.g. the average number of books read by college graduates last year in North America
Types of Data
- Numerical Data
○ Tell us how much of a given property each sample member exhibits
○ Magnitude and rank-order data
- Magnitude Data: Number indicating the amount of a property that exists along a continuum ("how much")
- Rank-Order (Ordinal) Data: Amounts of a property expressed as a rank relative to other individuals (1st,
2nd, 3rd)
- Categorical or Nominal Data
○ Information reflects mutually exclusive categories in which participants fall
○ Participants either display the attribute of they don't
E.g., male vs. female, fall vs. short, low mood vs. normative mood vs. elevated mood
Unit 1 Page 1 E.g., male vs. female, fall vs. short, low mood vs. normative mood vs. elevated mood
- Numerical (magnitude, ordinal) and categorical data are informative in their own way
○ Each form lends itself to certain statistical analyses
○ Choose carefully which type of data will help you answer your question (i.e., how you measure
constructs of interest
Descriptive Statistics
- Used to organize and summarize data
- Include measures of central tendency, measures of variability, and the correlation coefficient
Measures of CentralTendency
- Describe typical or average features of a distribution/set of values/data
○ 1) Mean-- the arithmetic average

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