Mode
the appropriate measure of central tendency for nominal variables
Probability Sampling
method of sampling that enables researchers to specify, for each case in the population, the probability of its inclusion in the sample
Two
In a normal distribution, the 95th percentile is how many standard deviations from the mean?
Population, standard deviation and sample size
What is standard error of the mean calculated using?
Area below the Z-Score
To find the percentile rank of a given score, what is it necessary to determine?
Difference between the areas beyond each Z-Score
In order to find the proportion of the area under the normal curve, between two z-scores that are both above the mean, it is necessary to examine what?
Cumulative Percentage Column
Which column is most useful when using frequency distribution to identify the interval containing the mean?
Area under the curve between any score and the mean
With normal curves, if you know the mean and the standard deviation, what are you able to calculate?
Measures of Central Tendency
categories or scores that describe what is average or typical of the distribution
Mode
the category or score with the highest frequency (or percentage) in the distribution
Type of scale used for mode
nominal scales
Percentile
a score below which a specific percentage of the distribution fall
Median
the score that divides the distribution into two equal parts so that half the cases are above it and half are below it
Type of scale used for mode
ordinal scales
Mean
a measure of central tendency that is obtained by adding up all of the scores and dividing by the total number of scores. It is the arithmetic average.
Scale type for Mean
interval-ratio measurement scales
Skewed Distribution
the mean may give misleading information on the central tendency because its value is affected by extreme scores in the distribution
General rule with Skewed Distribution
the mean, median and mode do not coincide
Measures of Variability
numbers that describe diversity or variability in the distribution of a variable
Normal Distribution
a bell-shaped and symmetrical theoretical distribution with the mean, median and mode all coinciding at its peak
Standard Z Score
the number of standard deviations that a given raw score is above or below the mean
Standard Normal Table
a table showing the area (as a proportion, which can be translated into a percentage) under the standard normal curve corresponding to any Z score or its fraction
Population
group that includes all the cases in which a researcher is interested
Sample
a subset of cases selected from a population
Symmetrical Distribution
when the distribution is symmetrical - any of the three values can be used
Positive Distribution
right tail is longer, has extreme high scores ("outliers"), mean is greater than median because it is influenced by high outliers
Negative Distribution
left tail is longer, has extreme low scores ("outliers"), mean is less than median because it is influenced by low outliers
Parameter
a measure used to describe the population distribution
Index of Qualitative Variation
a measure of variability for nominal variables - it is based on the ratio of the total number of differences in the distribution to the maximum number of possible differences within the same distribution
Range
a measure of variation in interval-ratio variables - it is the difference between highest (maximum) and the lowest (minimum) scores in the distribution
Interquartile range (IQR)
the width of the middle 50% of the distribution. - it is defined as the difference between the lower and upper quartile ranges (Q1 and Q3)
Box Plot
can visually represent the range, the IQR, the median, the lowest and the highest score - provides a way to visually examine the center, the variation and the shape of distributions of interval ratio variables
Variance
measure of variation for interval-ratio variables - it is the average of the squared deviations from the mean
Standard Deviation
measure of variation for interval-ratio variables - it is equal to the square root of the variance
Statistic
a measure used to describe the sample distribution
Probability Sampling
a method of sampling that enables the researcher to specify for each case in the population, the probability of is inclusion in the sample
Standard Normal Distribution
a normal distribution represented in standard Z scores - with the mean=0 and standard deviation=1
Simple Random Sample is a sample designed in such a way as to ensure what?
That every member of the population has an equal chance at being chosen and that every combination of N members has an equal chance of being chosen
K=
population size/sample size
Stratified Random Sample is a method of sampling obtained by what?
Dividing the population into subgroups based on one or more variables central to the analysis and then drawing a simple random sample from each of the subgroups
Proportionate Stratified Sample
the size of the sample selected from each subgroup is proportional to the size of that subgroup in the entire population
Disproportionate Stratified Sample
the size of the sample selected from each subgroup is disproportional to the size of the subgroup in the population
Sampling Distribution
theoretical probability distribution of all possible sample values for the statistics in which we are interested
Sampling Distribution of the Mean
theoretical probability distribution of sample means that would be obtained by drawing from the population all possible samples of the same size
Standard deviation of the sampling distribution is also called what?
Standard error of the mean
Estimation
a process whereby you select a random sample from a population and use a sample statistic to estimate a population parameter
Point Estimate
a sample statistic used to estimate the exact value of a population parameter
Confidence Interval
a range of values defined by the confidence level within which the population parameter is estimated to fall. Sometimes the confidence intervals are referred to as margin of error
Confidence Level
the likelihood, expressed as a percentage or probability, that a specified interval will contain the population parameter
Margin of Error
The radius of the confidence interval