PSYCH501 Module 1
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study population
clearly defined collection of people, animals, plants, or objects; usually a specific group of people

response variable
the measurement of the attribute of interest

ratio scale
 measurement with the following properties:
 0 represents comple absence
 ratio of any two scores correctly describes ratio of attribute quantites
 difference between two scores correctly describes difference in attribute quantities

interval scale
 measurement with the following properties:
 0 does not represent complete absence
 ratio of any two scores does not correctly describe ratio of attribute quantites
 difference between two scores correctly describes difference in attribute quantities

quantitative measurement
ratio or interval scale measurement

population parameter
single unknown numeric value that describes the measurements that could have been assigned to all N people in a specific study population

population mean
an unknown value; the average of all N scores that could have been assigned to all N people in a study population

random sample
a set of a study population of size n, selected in such a way that any set of size n has an equal chance of being selected

sample mean
an estimate of µ; the average of all scores from the sample

standard error

 value that numerically describes the accuracy of a parameter estimate

sample variance
 describes the variability of the scores in the sample

sample standard deviation
 estimate of ơ; describes the variability of the scores in a sample

confidence interval
range of values that is believed to contain an unknown population parameter value with some specified degree of confidence

null hypothesis
H0: µ = h; states that the mean is equal to some specified value

threedecision rule
_{1}a general hypothesis testing procedure in which one of the following decisions will be made: 1) accept H_{1, }2) accept H_{2}, 3) fail to reject H_{0}

test statistic
a value obtained from a ttest, used to determine whether or not to reject the null hypothesis

onesample ttest
a test of the null hypothesis applied to a single population mean

pvalue
a number determined by the test statistic; small pvalues correspond to high test statistics and the researcher may reject the null hypothesis if p is less than α (usually .05)

significance testing
an alternative to hypothesis testing where results are declared "significant" if the pvalue is less than some set value, usually .05

histogram
graph that visually displays a set of quantitative scores; displays the number of scores falling into specified ranges of scores

normal curve
 a curve in which:
 half of the scores are above the mean and half are below (the mean, median, and mode are identical)
 68% of scores are within 1 standard deviation above or below the mean
 95% of scores are within 2 standard deviations above or below the mean
 99.7% of scores are within 3 standard deviations above or below the mean

sampling distribution
the set of all possible sample means obtained from all possible samples in the study population

central limit theorem
states that if the sample size is sufficiently larg, the distribution of the sample means will be closely approximated by a normal distribution

unbiased estimate
an estimate which overestimates the population parameter with about the same tendency as it underestimates the population parameter

probability
a number on a 0 to 1 scale that describes the likelihood of an event

classical definition of probability
the proportion of all possible events that are of the type in question

power
the probability of rejecting the null hypothesis

type I error
rejecting the null hypothesis when, in reality, µ = h

prediction interval
 a range of plausible scores for one randomly selected person

planning value
a value obtained from experts, preliminary studies, or previoiusly published research

target population
a population of interest to the researcher from which the study population is taken

convenience sampling
nonrandom samlle obtained for ease or availability

random sampling assumption
requires the sample to be a random sample from the study population or some hypothetical population

independence assumption
requires that the responses from each participant in the study be independent of each other

normality assumption
requires that the scores in the study population have approximately a normal distribution

coefficient of skewness
numerically describes the skewness of a set of scores; zero if scores are symmetrical, positive if scores are skewed right, negative if scores are skewed left

coefficient of kurtosis
describes to degree to which a distribution is more less peaked than the normal distribution; equal to 3 in normal curve (coefficient  3 = excess kurtosis), excess kurtosis > 0 is highly peaked with long tails, excess kurtosis < 0 is lower peaked with short tails

data transformation
scores are all manipulated mathematically to reduce skewness and kurtosis