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, tile, porcelain and crystal glass industries. The HSE wants to know if there is any cause for concern that the workers may potentially be affected by silicosis (see below).  Data for four 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:

    Are there any differences in the health (as indicated by cell damage) of the workers in the sectors?
    What associations exist, if any, between length of service and recorded health effect?

The problem

Brick, tile, porcelain and crystal glass manufacturing along with many other industrial activities in the ceramics sector use quartz (a form of crystalline silica [CS]), feldspar and china clay as typical raw materials. Fine dusts formed during production activities, however, are a potential health hazard. One of the reasons for this 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 particular 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 HSL 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 of 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 measurement 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 the 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 workers 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 population satisfying these criteria, a sub-sample of 127 workers were randomly selected for blood testing, 38 from brick, 27 from tile, 30 from crystal glass and 32 from the porcelain sector .

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,T, P or C) and the individual (3 digit number)
C2 The sector in which the employee worked (brick, tile, porcelain or crystal glass)
C3 Length of service of each employee in the sector (in years)
C4 Age of each employee (in years)
C5 The percentage 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 which informs the HSE whether or not there is genuine evidence of difference in the potential health hazard between workers at the 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 no longer than 6 pages.

You are expected to:

    introduce the type of question you are facing including hypothesis testing
    produce appropriate descriptive/graphical summaries of the data
    justify your choice and undertake the correct statistical tests
    interpret any p-values and confidence 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 are the HSE asking exactly the right questions have potential confounding variables been adequately considered?

General advice

As I have previously indicated, only include computer output which you fully label and refer to in the text, and which you feel helps answer the problem. Please bear in mind my lecture on the use of graphics and tables.

Do not produce vast amounts of output from computer software. Only include computer output which you fully format, label, and discuss in the text. Be selective on use of Tables and graphics. Do not write the report like an instruction manual on how to operate Minitab focus on the interpretation and discussion of the output generated, not on how it was produced. Regarding referencing, you are not expected to cite a large amount of references in this kind of work. If however, you have read material that is relevant to your report, please cite it and reference it according to University Guidelines. Proof read your work before submitting it.

Finally and most importantly, it is the clarity and insight that you display in your interpretation and evaluation of the results obtained that is the key to obtaining a good grade.

Submission and deadline

You should submit on-line via Turnitin by 30th April 2014.

Assessment Criteria for Assignment 2