biostats exam 2

descriptive statistics

using various attributes of a population to describe it and using numbers to describe those attributes; describing different parameters. Includes measures of central tendency and measures of variation

mean

the arithmetic average of a distribution, obtained by adding the scores and then dividing by the number of scores. prof def: average

average

returns the average (arithmetic means) of its arguments

population mean

the sum of the values in the population divided by the population size.

Sample Mean (x̄)

Average value calculated from sample data.

Median

the middle score in a distribution; half the scores are above it and half are below it. prof def: the middle value

robust

not impacted by outliers / excludes outliers

Outliers

Numbers that are much greater or much less than the other numbers in the set. prof def: extreme, non-typical data value; quantitatively, a value more than 1.5 × IQR away from the interquartile range

Mode

the most frequently occurring score(s) in a distribution. prof def: the most common value

symmetrical distribution

if you put a line through the peak and both sides mirror each other; in a boxplot, median is in the middle and whiskers are about the same length. a distribution balanced around the center

asymmetrical distribution

not symmetrical. a distribution that is uneven on one side

skewed distribution

a representation of scores that lack symmetry around their average value. prof def: not symmetrical; one tail/whisker is longer

range

the difference between the highest and lowest scores in a distribution

Interquartile Range (IQR)

the difference between the first and third quartiles. prof def: the middle 50% of the data; end of the third quartile minus end of the first quartile

Quartiles

Values that divide a data set into four equal parts. prof def: four equal groupings

Interquartile

The difference between the upper and lower quartiles. prof def:the distance from the end of the first quartile to the end of the third quartile

Variance

standard deviation squared. prof def:measures dispersion, average squared distance from mean

inflection point

change in slope

Population Variance

Equals the mean squared deviation. Variance is the average squared distance from the mean. variance calculated using population data

Sample Variance

s² = Σ ( xi - x̄ )² / ( n - 1 ) variance calculated using sample data

Sums of Squares

the sum of the deviation scores for a distribution

standard deviation

a computed measure of how much scores vary around the mean score. prof def: distance from the population mean to the inflection point. the square root of variance; measures spread around the mean

Population Standard Deviation

the square root of the population variance

Sample Standard Deviation

the positive square root of the sample variance

coefficient of variance

A measure of the size of variability in relation to the size of the mean; calculated by dividing the standard deviation by the mean. standard deviation divided by the mean × 100

relative frequency

the fraction or percent of the time that an event occurs in an experiment. prof def: count divided by total; values range from 0 to 1. the proportion of observations in each category.

cumulative relative frequency

the sum of relative frequency up through, and including, the category of interest. prof def: running total of relative frequencies; ends at 1.0

adjacent values

the most extreme observations that still lie within the lower and upper limits. prof def: smallest and largest values that are not outliers

Accuracy

closeness to the true value

Precision

closeness of repeated measurements to each other

dispersion and variability

how spread out data values are

Histogram

a bar graph depicting a frequency distribution

polygon (frequency polygon)

a line graph connecting frequencies

cumulative frequency polygon

Displays cumulative frequency for continuous variables

continuous data

Data that can take on any value. There is no space between data values for a given domain. Graphs are represented by solid lines.

interval

grouped range of values

Box Plot

A diagram that shows the five number summary of a distribution.