chapter 12: descriptive statistics Flashcards
descriptive statistics
refers to a set of techniques for summarizing and displaying data for a sample.
distribution
the way scores are distributed across levels of a variable. unimodal or bimodal. symmetrical or skewed.
symmetrical
when a histogram’s left and right halves are mirror images of each other.
skewed
when a histogram’s peak is either shifted toward the upper end of its range and has a relatively long negative tail (negatively skewed) or the peak is shifted toward the lower end of its range and has a relatively long positive tail (positively skewed).
frequency table
a display of each value of a variable and the number of participants with that value.
histogram
a graphical display of a frequency distribution.
outlier
an extreme score that is much higher or lower than the rest of the scores in the distribution.
central tendency
is the middle of a distribution—the point around which the scores in the distribution tend to cluster. aka average.
mean
the average of a distribution of scores (M) where the sum of the scores are divided by the number of scores.
median
the midpoint of a distribution of scores in the sense that half the scores in the distribution are less than it and half are greater than it.
mode
the most frequently occurring score in a distribution.
variability
the extent to which the scores vary around their central tendency in a distribution.
range
a measure of dispersion that measures the distance between the highest and lowest scores in a distribution.
standard deviation
is the average distance between the scores and the mean distribution.
percentile rank
for any given score, the percentage of scores in the distribution that are lower than that score.
z score
is the difference between that individual’s score and the mean of the distribution, divided by the standard deviation of the distribution. it represents the number of standard deviations the score is from the mean.
effect size
describes the strength of a statistical relationship.
cohen’s d
the most widely used measure of effect size for differences between group or condition means, which is the difference between the two means divided by the standard deviation.
linear relationship
relationships between two variables whereby points on a scatterplots fall close to a single straight line.
nonlinear relationship
relationships between two variables in which the points on a a scatterplot do not fall close to a single straight line, but often fall along a curved line.
restriction of range
when one or both variables have a limited range in the sample relative to the population, making the value of the correlation coefficient misleading.
figures
graphical descriptions of data, such as pie charts, bar graphs, or scatterplots used to clearly and efficiently report a number of results.
bar graph
a graphical presentation of data as bars of varying size, generally used to present and compare the mean scores for two or more groups or conditions.
error bar
bars that represent the variability in each group or condition.
standard error
how different the population mean is likely to be from a sample mean. the standard deviation of the group divided by the square root of the sample size of the group.
line graph
graphs used when independent variable is measured in a more continuous manner (ex time) or to present correlations between quantitative variables when the independent variable has, or is organized into, a relatively small number of distinct levels.
scatterplot
a graph that presents correlations between two quantitative variables, one on the x-axis and one on the y-axis. scores are plotted at the intersection of the values on each axis.
correlation matrix
shows the correlation coefficient between pairs of variables in the study.
raw data
unanalyzed data that has several different forms—completed paper-and-pencil questionnaires, computer files filled with numbers or text, videos, or written notes which may have to be organized, coded, or combined in some way.
data file
data that has been entered into a spreadsheet and formatted in order to be analyzed.
planned analysis
used to test a relationship that you expected in your hypothesis.
exploratory analysis
an analysis used to examine the possibility that there might be relationships in the data that you did not hypothesize.
