Evidence-Based Practice for Nurses

and synthesize collected data. Calculations and information presented with

descriptive statistics must be accurate. Inferential statistics involve analysis

of data as the basis for predictions related to the phenomenon of interest.

Inferential statistics are used to make inferences or draw conclusions about a

population based on a sample. They are used to develop population parameters

from the sample statistics. For example, a researcher conducted a study on the

efficiency of vitamin C in preventing the common cold. Descriptive statistics

would be used to report that 60% of subjects in the experimental group had

fewer colds than did subjects receiving the placebo. The researcher would then

use inferential statistics to determine whether the difference in the number of

colds between the two groups was statistically significant. If it was, then it could

be inferred that taking vitamin C would be advantageous. Descriptive statistics

are used to provide information regarding univariate or bivariate analyses.

Univariate analysis is conducted to present organized information about

only one variable at a time and includes information regarding frequency

distributions, measures of central tendency, shape of the distribution, and

measures of variability, sometimes known as dispersion. Bivariate analysis

is performed to describe the relationship between two variables that can be

expressed in contingency tables or with other statistical tests. Multivariate

analysis is done when the researcher wants to examine the relationship among

three or more variables.

The results of descriptive analysis are frequently presented in table format,

and scientific notations are often used. Therefore, it may be helpful to review

common notations used in tables as shown in Table 13-1.

KEY TERMS

Statistics:

The branch of

mathematics that

collects, analyzes,

interprets, and

presents numerical

data in terms

of samples and

populations

statistics: The

numerical

outcomes and

probabilities

derived from

calculations on

raw data

descriptive

statistics:

Collection and

presentation of

data that explain

characteristics of

variables found in

the sample

inferential

statistics: Analysis

of data as the basis

for prediction

related to the

phenomenon of

interest

population

parameters:

Characteristics of

a population that

are inferred from

characteristics of a

sample

sample statistics:

Numerical data

describing

characteristics of

the sample

univariate analysis:

The use of statistical

tests to provide

information about

one variable

Symbol/Abbreviation Definition

f Frequency

M Mean

Mdn Median

n Number in subsample

N Total number in a sample

% Percentage

SD Standard deviation

z A standard score

TABLE 13-1

Statistical Symbols for Descriptive

Statistics

332 CHAPTER 13 What Do the Quantitative Data Mean?