What sample is large enough?
A great deal of statistical research has gone into this issue. As a
general rule, statisticians have found that for many population
distributions, once the sample size is at least 30, the sampling
distribution of the mean will be approximately normal. However, we
may be able to apply the central limited theorem for even smaller
sample sizes if a great deal of information is already known about the
Cluster analysis is used for classifying objects or cases, and sometimes
variables, into relatively homogeneous groups.
The groups of clusters are suggested by the data and are not defined a
Researches at Penn and Associates select variables for cluster analysis
based on hypothesis testing.
Data Collection Methods
There are several data collection methods and each have various
Email and web page surveys are the fastest methods, followed by
telephone interviewing. Interviewing by mail is the slowest.
Personal interviews are the most expensive followed by telephone and
then mail. Email and web page surveys are the least expensive for
Email and web page surveys offer fantastic advantages - cost, speed,
People are more likely to answer sensitive questions when interviewed
Factor analysis is a class of procedures used for reducing and
Each variable is expressed as a linear combination of the underlying
factors. Likewise, the factors themselves can be expressed as linear
combinations of the observed variables. The number of factors that
should be extracted can be determined a priori.
A rotation (varimax) transforms the factor matrix making it simpler
and easier to interpret.