Psych Stats Quiz #2 4/10/23

Question 1

normal distribution characteristics

Answer 1

unimodal, symmetric, asymptotic

Question 2

empirical rule

Answer 2

approx. 68% of values are within 1 standard deviation of the mean
approx. 95% of the values are within 2 standard deviations of the mean
approx. 99.7% of the values are within 3 standard deviations of the mean

Question 3

z scores (standard scores)

Answer 3

to make direct comparisons by transforming raw scores by standardizing them and converting them to a z score

Question 4

computing z score formula

Answer 4

Z = (X - mean)/standard deviation

Question 5

positive/negative z scores

Answer 5

a positive z score means above the mean, negative z score means below the mean

Question 6

properties of standard z scores

Answer 6

mean of a set of z scores is always 0 and the standard deviation is always 1
the distribution of a set of standardized z scores has the same shape as the unstandardized scores (raw)

Question 7

starting with z score and work backward

Answer 7

X = mean + z score (standard deviation)

Question 8

percentile scores

Answer 8

the proportion of people with scores less than or equal to a particular score, percentile scores are ways of summarizing a person’s location in a larger set of scores

Question 9

p-th percentile

Answer 9

a number such that at most p percent of the measurements are below it and at most 100-p percent of the data are above it
ex. 85th percentile is 340 meaning that 15% of the measurements in the data are above 340 and that 85% are below 340

Question 10

the disadvantage of standard scores

Answer 10

1) because a person’s score is expressed relative to the group, that same person can have different z-scores when assessed in different samples
2) if the absolute score (raw) is meaningful it would be obscured by transforming it into a relative metric
ex. IQ of 140 has a meaning that is lost when
transformed into a z score

Question 11

relative frequency from the mean

Answer 11

calculate the relative frequency of scores between a particular score and the mean by finding the z score and then subtracting it from the standard deviation

ex. GPA mean = 2, standard deviation = 0.5
Friend GPA = 1.5
1.5-2/0.5 = -1 —> 0.1587 or 15.87%
0.5 of the scores are below the mean so relative frequency between -1 and the mean = 0.5 - .1587 = 0.3415 or 34.15%

Question 12

relative frequency of scores between two scores

Answer 12

calculate z score and then subtract smallest from the biggest to get the percentage of scores in between the two numbers
ex. x = 2.25 and x = 3.5
2.25 -2/5 = 0.5
3.5-2/5 = 3
both scores are above the mean (+)
z of 0.5 = 69.15% and z of 3.0 = 99.86%
0.9986-0.6915 = .3071 or 30.71% of the GPA is in between the two scores

Question 13

characteristics of z scores

Answer 13

a measure of relative standing in distribution
facilitate comparison across distributions by standardizing the meaning of zero and the meaning of one unit

Question 14

inferential statistical procedure

Answer 14

uses a random sample from a population to make inferences about the population

Question 15

parameter estimation

Answer 15

uses data in a random sample to estimate a parameter of the population from which the sample was drawn

Question 16

hypothesis-testing

Answer 16

requires the formulation of two opposing hypotheses about the population of interest
data from random samples are used to determine which of the opposing hypotheses is likely to be correct

Question 17

parametric hypothesis testing

Answer 17

the hypotheses refer to population parameters, usually the mean of the variance of the population

Question 18

nonparametric hypothesis testing

Answer 18

the specific hypotheses refer to the shape or location (central tendency) of the populations, rather than specific parameters

Question 19

steps to produce a random sample

Answer 19

write observations on paper and draw from a hat because each observation has an equal chance of being picked out of the hat

Question 20

biased sampling

Answer 20

ex. a university dean wants to gather data on graduation requirement changes and stops every 5th student entering the student union
seems random but is biased because the students that frequent the library would be systematically excluded from the sample

Question 21

overgeneralization

Answer 21

an inference about a population other than the one that was randomly sampled

Question 22

event

Answer 22

a value or range of values on the variables being measured

Question 23

simple probabilities

Answer 23

numbers that indicate the likelihood that an event occurs in a simple random observation from population

Question 24

mutually exclusive events

Answer 24

cannot occur on the same observation

Question 25

conditional probability

Answer 25

the probability of an event conditional upon the occurrence of some other event or the existence of a particular state of affairs