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Library Administration and Management

Notes A common goal for a statistical research project is to investigate causality, and in particular to
draw a conclusion on the effect of changes in the values of predictors or independent variables
on dependent variables or response. There are two major types of causal statistical studies:
Experimental Studies, and
Observational Studies.
In both types of studies, the effect of differences of an independent variable (or variables) on the
behaviour of the dependent variable are observed. The difference between the two types lies in
how the study is actually conducted. Each can be very effective.

Experimental Studies

An experimental study involves taking measurements of the system under study, manipulating
the system, and then taking additional measurements using the same procedure to determine if
the manipulation has modified the values of the measurements. In contrast, an observational
study does not involve experimental manipulation. Instead, data are gathered and correlations
between predictors and response are investigated.
Experiments
The basic steps of a statistical experiment are:

Planning the research, including finding the number of replicates of the study, using the
following information: preliminary estimates regarding the size of treatment effects,
alternative hypotheses, and the estimated experimental variability. Consideration of the
selection of experimental subjects and the ethics of research is necessary. Statisticians
recommend that experiments compare (at least) one new treatment with a standard
treatment or control, to allow an unbiased estimate of the difference in treatment effects.
Design of experiments, using blocking to reduce the influence of confounding variables,
and randomized assignment of treatments to subjects to allow unbiased estimates of
treatment effects and experimental error. At this stage, the experimenters and statisticians
write the experimental protocol that shall guide the performance of the experiment and
that specifies the primary analysis of the experimental data.

Performing the experiment following the experimental protocol and analysing the data
following the experimental protocol.

Further examining the data set in secondary analyses, to suggest new hypotheses for
future study.

Documenting and presenting the results of the study.
Observational Studies

In epidemiology and statistics, an observational study draws inferences about the possible
effect of a treatment on subjects, where the assignment of subjects into a treated group versus a
control group is outside the control of the investigator. This is in contrast with experiments,
such as randomized controlled trials, where each subject is randomly assigned to a treated
group or a control group. The assignment of treatments may be beyond the control of the
investigator for a variety of reasons:
A randomized experiment would violate ethical standards. Suppose one wanted to
investigate the abortion – breast cancer hypothesis, which postulates a causal link between

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