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Unformatted text preview: to make inferences about… on the basis of a par@cular sample Sample: a part of the popula@on for which a researcher collects data and knows a set of scores 10 9/10/13 Why do we study samples, rather than a popula@on? Prac@cality Goal is to make generaliza@ons or predic@ons about events beyond our reach Try to study a sample of people who are representa@ve of the popula@on of interest Random selec@on is ideal From the full popula@on of interest, randomly select individuals to be included in sample OCen is imprac@cal or impossible to obtain a truly random sample ▪ Instead, try to get a sample that is not systema@cally unrepresenta@ve of popula@on in any known way ▪ Avoid haphazard selec@on Sta@s@cal terminology varies for sample sta@s@cs versus popula@on parameters Population Parameter Sample Statistics Scores from entire population Scores of sample only (Usually unknown) (Calculated from known data) µ (mu) M σ (sigma) SD (sigma squared) SD 2 Mean
Standard
Deviation
Variance σ2 11 9/10/13 Probability deﬁni@on: Expected rela@ve frequency of an outcome Outcome: result of experiment/situa@on Frequency: how many @mes something happens Rela@ve frequency: number of @mes something happens rela@ve to the number of @mes it could have happened Expected rela@ve frequency: what you expect to get in the long run if you repeat the experiment/situa@on many @mes Long
run rela@ve frequency interpreta@on of probability vs. subjec@ve interpreta@on of probability Probability = Possible successful outcomes All possible outcomes What is the probability of genng a 4 when you roll a die? 1/7 = 0.14 What is the probability of choosing a heart from a deck of cards? 13/52 = 1/4 = 0.25 Range: 0 to 1, also represented 0
100% Probability as the likelihood of occurrence Impossible to Certain 12 9/10/13 Probability is symbolized as the le]er p, and usually represented as a decimal (0 to 1) rather than a percent p = .5 represents a 50/50 chance p < .05 represents “the probability is less than .05” The normal distribu@on can be thought of as a probability distribu@on 15 70 85 100 115 130 You apply to 20 graduate programs, 10 of which are in clinical psychology, 5 of which are in counseling psychology, and 5 of which are in social work. You get a message from home that you received a le]er from one of the programs. Give the probabili@es that it is from A clinical psychology program. A counseling psychology program. From any other program besides social work. 13 9/10/13 A student wants to study the eﬀect of stress on memory. He posts a sign
up sheet for anyone willing to par@cipate. The student is conduc@ng: a. Random selec@on b. Haphazard selec@on c. Speciﬁed selec@on d. Quota selec@on In sta@s@cal language, a scoop of water drawn from a ﬁsh tank full of tropical saltwater ﬁsh to determine the exact salt content of the water is: a. Popula@on b. Parameter c. Sample d. Popula@on distribu@on In a normal curve, approximately __?__ percentage of scores are lower than 2 standard devia@ons below the mean. In a normal curve, approximately 68% of the scores are between a z
score of __?__ and a z
score of __?__. In a normal curve, what percentage of scores fall within 2 standard devia@ons of the mean? 14...
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This note was uploaded on 03/24/2014 for the course PSY 21201 taught by Professor Bernard during the Winter '13 term at SUNY Stony Brook.
 Winter '13
 bernard
 Psychology

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