Chapter 2 Basic Concepts

2 Chapter 2 Basic Information Major Points Scales of measurement Scales of measurement Variables Variables Random sampling Random sampling Notation Notation Review questions Review questions

3 Chapter 2 Basic Information Scales of Measurement Numbers are used to identify, to represent position in an ordered series, or to quantify Numbers are used to identify, to represent position in an ordered series, or to quantify Nominal scales: name or identify Nominal scales: name or identify Ordinal scales: place objects in order Ordinal scales: place objects in order Interval scales: equal intervals between points on the measurement scale Interval scales: equal intervals between points on the measurement scale Ratio scales: also have absolute zero Ratio scales: also have absolute zero What does it all mean? What does it all mean?

4 Chapter 2 Basic InformationVariables Define variable Define variable Property of an object or event that can take on different values Property of an object or event that can take on different values Discrete variable Discrete variable Variable that can take on only a small set of possible values, there are gaps between values. Variable that can take on only a small set of possible values, there are gaps between values. Continuous variable Continuous variable Variable that can take on any value. Variable that can take on any value. Cont.

5 Chapter 2 Basic Information Variables --cont. Independent variables Independent variables Those variables controlled by the experimenter Those variables controlled by the experimenter Dependent variables Dependent variables Those variables being measured Those variables being measured The data or score The data or score

6 Chapter 2 Basic Information Random Sampling Inferring from sample to population Inferring from sample to population Random implies “equal chance of being selected” Random implies “equal chance of being selected” Distinguish between random sampling and random assignment Distinguish between random sampling and random assignment How to draw a random sample How to draw a random sample A big hat A big hat Random number tables Random number tables Computer generated Computer generated

7 Chapter 2 Basic InformationNotation Variable names Variable names X and Y X and Y Individual values Individual values X versus X i X versus X i Summation notation Summation notation  X  X  X 2  X 2 (  X) 2 (  X) 2  XY  XY  X  Y  X  Y Constant Constant

8 Chapter 2 Basic Information Hypothetical data on family size by decade of 20th century: does family size decrease as decade increases? Complete the following… Please do not forget to include the sum of each column at the bottom.

9 Chapter 2 Basic Information Hypothetical data on family size by decade of 20th century: does family size decrease as decade increases?

10 Chapter 2 Basic Information Review Questions Give an example of a nominal, ordinal, interval, and ratio scale. Give an example of a nominal, ordinal, interval, and ratio scale. What is the scale relationship between hours of sunlight and quality of life? What is the scale relationship between hours of sunlight and quality of life? Why is random assignment more important than random sampling? Why is random assignment more important than random sampling? Cont.

11 Chapter 2 Basic Information Review Questions -- cont. Why are  X 2 and (  X) 2 different? Why are  X 2 and (  X) 2 different? What happens when you multiply by a constant, or add a constant? (consult text) What happens when you multiply by a constant, or add a constant? (consult text)

Handouts Complete the Scales of Measurement Assignment for practice