Whether HSE is genuine or not in the evidence of difference in the potential health hazard between workers at the two operations

Test book : Author : Dytham C, 1999, Choosing and using statistics: a biologist’s guide. Blackwell science: oxward (ebook)
Test book: Author: Aveyard H, 2010, Doing a literature review in health and social care. A practical guide. Maidenhead: McGraw-Hill open university press (ebook)
The Health and Safety Executive (HSE), commissions you to analyse information obtained from a
study by the Health and Safety Laboratory (HSL) of workers from brick and tile industries. The HSE
wants to know if there is any cause for concern that the worker
s may potentially be affected by
silicosis (see below). Data for two sectors has been provided which the HSE hope may shed light
on any potential problems.
There are
two key questions
which the HSE require you to address:
•
Is there any difference in th
e health (as indicated by cell damage) of the workers in the two
operations?
•
What associations exist, if any, between length of service and recorded health effect?
Background
The problem
Brick and tile manufacturing along with many other industrial activ
ities in the ceramics sector use
quartz (a form of crystalline silica [CS]), feldspar and china clay as typical raw materials. Fine dusts
formed during brick and tile production activities, however, are a potential health hazard. One of
the reasons for thi
s is that the smallest particles in fine dusts may contain Respirable Crystalline
Silica (RCS) formed from the quartz component of the raw materials. It is known that prolonged
and excessive exposure to RCS
–
containing dusts may cause silicosis, a particula
r form of
pulmonary fibrosis leading to incapacity and premature death. As such the HSE takes the issue
seriously and has undertaken a preliminary study via the agency of the HLS to look into any
potential problems and it is the results of this study that
you are commissioned to analyse.
The use of LDH as a warning sign
Lactate dehydrogenase (LDH) is an intracellular enzyme. It oxidizes lactate in the presence of
NADH
(reduced form of nicotinamide adenine dinucleotide)
or reduces pyruvate in the presence o
f
NAD (oxidised form of
NADH)
. It is used clinically to determine cell damage in a number of organs
including heart, liver, muscle and blood. Elevations in LDH release are known to be associated
with increased levels of cell membrane permeability and its m
easurement is therefore considered a
good indicator of the extent of cell damage. It is deemed to be a useful indicator of the initial stages
of cell damage caused by trauma from introduction of alien particles to cells including RCS
–
containing dusts. In t
he data presented herein, LDH release in blood cells has been recorded and
the results have been calculated to produce a % cell damage figure.
The study group and the data collected
The HSL in undertaking the study stipulated three key criteria for work
ers to take part in the study,
namely:
•
They must not have worked in both brick and tile works.
•
They worked in areas of tile or brick production (i.e. not in an office or other areas away
from the industrial activity).
•
They did not smoke.
From the popula
tion satisfying these criteria, a sub
–
sample of 65 workers
was
randomly selected
for blood testing, 38 from brick operations, and 27 from tile operations.
In the Minitab worksheet the results of the study are shown in 5 columns of data.
C1
–
A worker
ID, identifying the sector (letter B or T) and the individual (3 digit number)
C2
–
The sector in which the employee worked (brick or tile)
C3
–
Length of service of each employee in the sector (in years)
C4
–
Age of each employee (in years)
C5
–
The perce
ntage of damaged cells for each employee as calculated by results of the LDH
assay (%)
Your task
You a required to produce a coherent, concise, well presented and well structured
report that
informs the HSE
whether or not there is genuine evidence of diff
erence in the potential health
hazard between workers at the two operations.
Further, you are required to report on
whether there is any association between worker length of
service in the industry and the potential damage to their health.
In concluding
the report you cannot
assume that the HSE understands statistical methods in detail and you will therefore have to
summarise your findings in plain non
–
technical language. The length of the report should be
in the
region of 4 to 8
pages.
You are expected
to:
•
introduce the type of question you are facing including
an explanation of
hypothesis testing
•
produce appropriate descriptive/graphical summaries of the data
•
justify your choice and undertake the correct statistical tests
•
interpret any p
–
values and con
fidence intervals
and correlation co
efficients correctly
•
arrive at brief and clear conclusions that directly answer the problem
•
finally, you are free to explore and will be credited for any further analyses of the data you
deem worthy of investigation
–
a
re the HSE asking exactly the right questions?