Page 68 - Anthropometry, Apparel Sizing and Design

Developing apparel sizing system using anthropometric data 97

4.2.2 Step 2: Anthropometric planning

Anthropometric planning comprises the preliminary study, sample size calculation,
and fieldwork coordination. The first purpose of the preliminary study is to test the
whole process of measuring, to understand the nature of the survey, and to solve
any potential problems before undertaking the real anthropometric survey. The second
purpose is to take the measurements needed to calculate the sample size for the anthro-
pometric survey.
4.2.2.1 Preliminary survey

The preliminary survey can be conducted on a small scale and is usually called the
pilot study. The sample size can range from 30 to 100 people. The main objective
is to collect sufficient body measurements to calculate the sample size needed for
the real anthropometric survey.
One common technique that can be used to calculate the sample size for a study is the
proportionate stratified random sampling technique (Hair et al., 1998; Bartlett et al.,
2001). Proportionate stratified sampling refers to taking the same proportion (sample
fraction) from each stratum (Tabachnick and Fidell, 2007). For example, say there
are three groups of students: group A with 100 people, group B with 50 people, and
group C with 30 people. These groups are referred to as strata. The sample units are
randomly selected from each stratum based on proportion. For example, a proportion
of 10% from each group (strata) would mean that 10 people were taken from group
A, 5 people from group B, and 3 people from group C. The stratum group for this study
was based on two groups, age (7–17years old) and gender (female and male).
A study can have, for example, four demographic variables: age, gender, ethnic group,
and geographical area (rural and urban). If the study is focused on two factors such as age
and gender, then the proportionate sample size will reflect the distribution of age and
gender groups in the real population. The other two parameters, ethnic group and geo-
graphical area, can be selected according to simple random technique with the targeted
number of subjects calculated from the proportionate sample size (Bartlett et al., 2001).
Data obtained from the preliminary study can be analyzed to calculate the total
sample size using the stratified random sampling formula (Eq. 1.1). Then the number
of subjects to be sampled from six gender and age groups can be calculated using pro-
portionate sampling based on the actual number of subjects present in the geograph-
ical area of interest. The steps are given in detail later.
4.2.2.2 Sample size determination

The sample size for a survey can be calculated using the stratified random sampling
formula as shown in Eq. (1.1) (Scheaffer et al., 2005):

l
X
2 2
N σ =a i
i i
i¼1
n ¼ (1.1)
l
X
2
2 2
N D + N σ
i i
i¼1