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# Chapter 1 PSY 205

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This 9 page Class Notes was uploaded by Yousra Notetaker on Sunday January 24, 2016. The Class Notes belongs to PSY 205 at Eastern Michigan University taught by Albright, Jeremy in Winter 2016. Since its upload, it has received 41 views. For similar materials see Quantitative Methods in Psychlogy at Eastern Michigan University.

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Date Created: 01/24/16

Chapter 1 Introduction to Statistics 12416 647 PM Statistics Science and Observations 0 Statistics means statistical procedures 0 Uses of Statistics 0 Organize and summarize information 0 Determine exactly what conclusions are justified based on the results that were obtained 0 Goals of statistical procedures 0 Accurate and meaningful interpretation 0 Provide standardized evaluation procedures Populations and Samples Population 0 The set of all the individuals of interest in a particular study Vary in size often quite large 0 Greek letters for parameters Sample 0 A set of individuals selected from a population 0 Usually intended to represent the population in a research study 0 Latin letters for statistics Variables and Data Variable 0 Characteristic or condition that changes or has different values for different individuals Distinguished from a Constant that does not vary Data plural 0 Measurements or observations of a variable Data set 0 A collection of measurements or observations A datum singular A single measurement or observation Commonly called a score or raw score Parameters and Statistics Parameter A value usually a numerical value that describes a population Derived from measurements of the individuals in the population Statistic A value usually a numerical value that describes a sample Derived from measurements of the individuals in the sample Descriptive amp Inferential Statistics Descriptive statistics Summarize data Organize data Simplify data Familiar examples 0 Tables 0 Graphs o Averages Inferential statistics 0 Study samples to make generalizations about the population Interpret experimental data 0 Common terminology o Margin of errorquot 0 Statistically significantquot Sampling Error 0 Sample is never identical to population 0 Sampling Error 0 The discrepancy or amount of error that exists between a sample statistic and the corresponding population parameter 0 Example Margin of Error in Polls 0 This poll was taken from a sample of registered voters and has a margin of error of plusorminus 4 percentage pointsquot Data Structures Research Methods and Statistics Individual Variables A variable is observed 0 Statistics describe the observed variable 0 Category andor numerical variables Relationships between variables 0 Two variables observed and measured 0 One of two possible data structures used to determine what type of relationship exists Relationships Between Variables Data Structure I The Correlational Method 0 One group of participants 0 Measurement of two variables for each participant 0 Goal is to describe type and magnitude of the relationship 0 Patterns in the data reveal relationships Nonexperimental method of study Data Structure II Comparing two or more groups of Scores 0 One variable defines the groups 0 Scores are measured on second variable 0 Both experimental and nonexperimental studies use this structure 0 Experimental Researcher controls which group subjects fall into 0 Quasiexperimental Nature assigns groups eg gender race country of origin Correlational Method Limitations 0 Can demonstrate the existence of a relationship 0 Does not provide an explanation for the relationship 0 Most importantly does not demonstrate a causeandeffect relationship between the two variables Experimental Method Goal of Experimental Method 0 To demonstrate a causeandeffect relationship Manipulation The level of one variable is determined by the experimenter Control rules out influence of other variables 0 Participant variables 0 Environmental variables IndependentDependent Variables Independent Variable is the variable manipulated by the researcher 0 Independent because no other variable in the study influences its value Dependent Variable o is the one observed to assess the effect of treatment 0 Dependent because its value is thought to depend on the value of the independent variable Experimental Method Control Methods of control 0 Random assignment of subjects 0 Matching of subjects not covered in this class 0 Holding level of some potentially influential variables constant not covered in this class Control condition 0 Individuals do not receive the experimental treatment 0 They either receive no treatment or they receive a neutral placebo treatment 0 Purpose to provide a baseline for comparison with the experimental condition Experimental condition 0 Individuals do receive the experimental treatment Nonexperimental Methods Nonequivalent Groups 0 Researcher compares groups 0 Researcher cannot control who goes into which group Pretest Posttest Individuals measured at two points in time o Researcher cannot control influence of the passage of time Independent variable is quasiindependent Variables and Measurement 0 Scores are obtained by observing and measuring variables that scientists use to help define and explain external behaviors The process of measurement consists of applying carefully defined measurement procedures for each variable Statistical Notation 0 Statistics uses operations and notation you have already learned 0 Statistics also uses some specific notation 0 Scores are referred to as X and Y o N is the number of scores in a population 0 n is the number of scores in a sample Scales of Measurement Nominal 0 all three measures of dispersion require data to be ranked or summed none of them are appropriate for data measured at the nominal level Ordinal level 0 The range and interquartile range are appropriate 0 The interquartile range is usually preferable Intervalratio level 0 All three measures of dispersion we have examined are appropriate 0 The standard deviation is usually preferable Summation Notation Summation A sum is represented by the Greek letter capital Sigma or 2 The sum of all of the individual values of X is represented by 2X 2XX1X2X3X4X5X6X7X8 X1X2X8 282227209 N Xi ALSO WRITTEN As i 0 This notation is useful if we want to sum specific observations for example the sum of the scores for students 3 through 6 can be written as 6 2X1 X3X4X5X6 100 i3 o If there are no subscripts on 2 assume the summation is over all individuals 0 Write the average score in summation notation 0 Many statistical procedures sum add up a set of scores 0 The summation sign 2 stands for summation o The Z is followed by a symbol or equation that defines what is to be summed o Summation is done after operations in parentheses squaring and multiplication or division 0 Summation is done before other addition or subtraction Orders of Operation remember PEMDAS 1 Any calculation contained within parentheses is done first 2 Squaring or raising to other exponents is done second 3 Multiplying andor dividing is done third A series of multiplication andor division should be done in order from left to right 4 Summation using the 2 is done next 5 Finally any other addition andor subtraction is done 12416 647 PM 12416 647 PM

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