Page 123 - Foundations of Cognitive Psychology : Core Readings

126 Daniel J. Levitin

3. Privacy and confidentiality. The experimenter must carefully guard the
data that are collected and,whenever possible,code and store the data in
such a way that subjects’ identities remain confidential.
4. Fraud. This principle is not specific to human subjects research,but
applies to all research. An essential ethical standard of the scientific com-
munity is that scientific researchers never fabricate data,and never know-
ingly,intentionally,or through carelessness allow false data, analyses,or
conclusions to be published. Fraudulent reporting is one of the most seri-
ous ethical breaches in the scientific community.

6.8 Analyzing Your Data

6.8.1 Quantitative Analysis
Measurement Error Whenever you measure a quantity,there are two compo-
nents that contribute to the number you end up with: the actual value of the
thing you are measuring and some amount of measurement error,both human
and mechanical. It is an axiom of statistics that measurement error is just as
likely to result in an overestimate as an underestimate of the true value. That is,
each time you take a measurement,the error term (let’s call it epsilon)is just as
likely to be positive as negative. Over a large number of measurements,the
positive errors and negative errors will cancel out,and the average value of
epsilon will approach 0. The larger the number of measurements you make,the
closer you will get to the true value. Thus,as the number of measurements
approaches infinity,the arithmetic average of your measurements approaches
the true quantity being measured. Suppose we are measuring the weight of a
sandbag.
Formally,we would write:

n ! y; e ¼ 0
where e ¼ the mean of epsilon,and
n ! y; w ¼ w

where w ¼ themeanofall theweightmeasurementsand w ¼ thetrueweight.
When measuring the behavior of human subjects on a task,you encounter
not only measurement error but also performance error. The subjects will not
perform identically every time. As with measurement error,the more observa-
tions you make,the more likely it is that the performance errors cancel each
other out. In psychoacoustic tasks the performance errors can often be rela-
tively large. This is the reason why one usually wants to have the subject per-
form the same task many times,or to have many subjects perform the task a
few times.
Because of these errors,the value of your dependent variable(s) at the end
of the experiment will always deviate from the true value by some amount.
Statistical analysis helps in interpreting these differences (Bayesian inferencing,
meta-analyses,effect size analysis,significance testing) and in predicting the
true value (point estimates and confidence intervals). The mechanics of these