Statistics Flashcards
sample
A sample is selected to represent the population in a research study; helps answer questions about a population.
variable
characteristic or condition that can change or take on different values.
discrete variables
(such as class size) consist of indivisible categories (weird when it is represented by a fraction
continuous variables
(such as time or weight) are infinitely divisible into whatever units a researcher may choose. Also, that can be legitimately measured.
goal of experiment
Goal of an experiment is to demonstrate a cause-and-effect relationship between two variables; that is, to show that changing the value of one variable causes changes to occur in a second variable.
IV and DV
In an experiment, the manipulated variable is called the independent variable and the observed variable is the dependent variable.
non-experimental or quasiexperimental
non-experimental or quasi-experimental, are similar to experiments because they also compare groups of scores. These studies do not use a manipulated variable to differentiate the groups. Instead, the variable that differentiates the groups is usually a pre-existing participant variable (such as male/female) or a time variable (such as before/after).
Similar to correlational research because they simply demonstrate and describe relationships
positively skewed
In a positively skewed distribution, the scores tend to pile up on the left side of the distribution with the tail tapering off to the right.
negatively skewed
In a negatively skewed distribution, the scores tend to pile up on the right side and the tail points to the left.
percentile rank
The percentile rank for a particular X value is the percentage of individuals with scores equal to or less than that X value. When an X value is described by its rank, it is called a percentile.
nominal
name only, categorical; only permit you to determine whether two individuals are the same or different. (i.e. male/female; diagnosis)
ordinal
rank ordered (e.g. height shortest to tallest); tell you the direction of difference between two individuals.
spearman correlation (i.e. class rank)
interval
consistent intervals between numbers but no absolute zero (i.e. IQ); identify the direction and magnitude of a difference
ratio
interval plus absolute zero – height in inches; identify the direction and magnitude of differences and allow ratio comparisons of measurements
reliability
same results with repeated administrations
validity
measures what it says it measures- taps into the construct
standard error of the mean (SEM)
measure of variability; the average expected difference between sample means (i.e. M1 – M2 expected)
confidence interval
a type of interval estimate of a population parameter and is used to indicate the reliability of an estimate. Certain factors may affect the confidence interval size including size of sample, level of confidence, and population variability. A larger sample size normally will lead to a better estimate of the population parameter.
sampling error
The discrepancy between a sample statistic and its population parameter is called sampling error.
central tendency in normal distribution
a statistical measure that determines a single value that accurately describes the center of the distribution and represents the entire distribution of scores. The goal of central tendency is to identify the single value that is the best representative for the entire set of data. Allows researchers to summarize or condense a large set of data into a single value (thus a descriptive statistic).
mean and a mean in skewed data
Mean: the average; most commonly used; requires scores that are numerical values measured on an interval or ratio scale
When a distribution contains a few extreme scores (or is very skewed), the mean will be pulled toward the extremes (displaced toward the tail).
median
Median: If the scores in a distribution are listed in order from smallest to largest, the median is defined as the midpoint of the list; values measured on an ordinal, interval, or ratio scale
Relatively unaffected by extreme scores
mode
the most frequently occurring category or score in the distribution; any scale of measurement: nominal, ordinal, interval, or ratio
what will be equal in a symmetrical distribution
the mean and median will always be equal