Research
methodology
75
Data analysis – quantitative data
Analysis of quantitative data involves the production and interpretation of frequencies, tables,
graphs, etc., that describe the data.
1. Frequency counts
From the data master sheets, simple
tables can be made with frequency counts for each
variable. A frequency count is an enumeration of how often a certain measurement or a
certain answer to a specific question occurs.
For example,
Smokers 51
Non-smokers 93
Total
144
If numbers are large enough it is better to calculate the frequency distribution in percentages
(relative frequencies)
: 51/144 x 100 = 35% are smokers and 93/144 x 100 = 65% non-
smokers. This makes it easier to compare groups than when only absolute numbers are
given.
In other words, percentages standardise the data.
It is usually necessary to summarise the data from numerical variables by dividing them into
categories. This process may include the following steps:
(1) Inspect all the figures: What is their range? (The range is the difference
between the largest and the smallest measurement.)
(2) Divide the range into three to five categories. You can either aim at having a
reasonable number in each category (e.g. 0-2 km, 3-4 km, 5-9 km, 10+ km
for home-clinic distance) or you can define the categories in such a way that
they are each equal in size (e.g., 20-29 years, 30-39 years, 40-49 years,
etc.). Sometimes one looks actively for a ‘critical’ value,
when making
different categories. For example, in a study relating family income to
prevalence of diarrhoea over a certain period,
there appeared to be no
statistical relation when income was arbitrarily subdivided into four
categories. When the
average income was calculated, however, this
Research methodology
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appeared to be a critical value. The children in families with an income
above average had had significantly less diarrhoea than the children in
families with an income below average.
(3) Construct a table indicating how data are grouped and count the number of
observations in each group.
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