Introduction:
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 more than one industry
• They worked in areas of actual production (i.e. not in an office or other areas away from the industrial activity).
• They had not smoked historically or currently
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?
worker ID sector length of service (years) age (years) % damaged cells
B323 brick 13 57 1.3
B324 brick 1 35 1.2
B325 brick 10.17222224 64 0.6
B326 brick 2 34 0.35207807
B327 brick 2.446823892 26 0.3
B328 brick 3 24 2
B329 brick 13 44 0.633876697
B330 brick 8.175885209 24 0.414168654
B331 brick 24 43 4.3
B332 brick 6 56 2.01604888
B333 brick 0.539553847 23 0.2
B334 brick 2.466619598 51 2.721072948
B335 brick 19 40 0.2
B336 brick 7.205074716 31 2.607234271
B337 brick 12 29 3.314161098
B338 brick 10 34 0.352532839
B339 brick 1 18 0.595044196
B340 brick 3 26 2.3
B341 brick 23.32145497 65 2.599286581
B342 brick 11 47 0.703916403
B343 brick 4 25 0.4
B344 brick 5 27 3.555735741
B345 brick 6.380664215 28 1.4
B346 brick 1.197184049 27 1.972830638
B347 brick 3 30 2.035834392
B348 brick 11.34698746 45 0.724646831
B349 brick 14.45928287 64 2.78833789
B350 brick 18.25232769 55 1.340745686
B351 brick 6.494044232 40 3.226793059
B352 brick 3 46 0.3
B353 brick 1 21 0.405424264
B354 brick 1 35 0.576491674
B355 brick 10 43 2.152212798
B356 brick 6 28 1.2
B357 brick 11.19477808 28 1.416950217
B358 brick 4 26 1.73598537
B359 brick 34 60 3.7
B360 brick 10.64858781 47 2.095141256
T129 tile 7 30 1.1
T130 tile 10.8629815 30 1.4
T131 tile 15 40 1
T132 tile 4 47 0.3
T133 tile 14.47172085 46 1.1
T134 tile 24 59 1.5
T135 tile 3 42 0.2
T136 tile 1 50 1.8
T137 tile 1.978288806 23 1.1
T138 tile 8.833887325 39 1.1
T139 tile 8.107908927 25 0.5
T140 tile 7 32 0.9
T141 tile 2.702858074 49 1
T142 tile 13 62 2.5
T143 tile 1 17 0.2
T144 tile 6.226062453 52 1.1
T145 tile 11.3271056 63 0.6
T146 tile 17.54094615 49 1.4
T147 tile 8.287174887 25 1
T148 tile 12 29 1.2
T149 tile 3 31 0.3
T150 tile 20.24408395 37 4.3
T151 tile 2.353855551 47 2.1
T152 tile 27.2279628 65 4.5
T153 tile 10 48 1.1
T154 tile 22.65437058 40 2.3
T155 tile 2.557845585 49 0.5
P023 porcelain 8.371485248 40.5558592 1.886405148
P024 porcelain 19 55 2.992972544
P025 porcelain 11.59619063 34.61112704 0.862168524
P026 porcelain 8.090693036 45.6128605 0.995702446
P027 porcelain 7.102451133 26.12686753 0.502547151
P028 porcelain 7.428987956 39.71387317 1.177289233
P029 porcelain 14.18550293 55 3.675640746
P030 porcelain 2.858025141 24 0.777680308
P031 porcelain 4.760865564 44.35678183 1.823722308
P032 porcelain 8.201644009 38.00057188 1.310549102
P033 porcelain 10.22612608 34.22287547 3.4
P034 porcelain 24 54 2.251796861
P035 porcelain 2.582331791 40.67579658 0.889105367
P036 porcelain 12 41.09642099 1.18117711
P037 porcelain 3.927737642 23.13349528 2.278443748
P038 porcelain 17 39.0033046 2.280087156
P039 porcelain 9.69111684 48.29395928 2.03976138
P040 porcelain 5.608429472 36.98603761 0.964676691
P041 porcelain 7.93275577 38.48671775 1.945007662
P042 porcelain 25 64 2.7
P043 porcelain 9.806492426 24.21324053 1.75142032
P044 porcelain 2.467252664 40.90654769 1.068146815
P045 porcelain 11.01922419 37.26758688 0.489062015
P046 porcelain 13.81743106 34.87322563 3.6
P047 porcelain 10.43379123 38.51412721 1.60590288
P048 porcelain 9.69313805 25.76867433 2
P049 porcelain 4.469880948 39.86441134 2.176767505
P050 porcelain 3.961242472 24.4306443 1.969909764
P051 porcelain 11.12978142 45.08924148 1.615387386
P052 porcelain 6.724451345 30.7093758 1.349825858
P053 porcelain 10.80964825 39.91628014 2.3
P054 porcelain 11.39836959 30.84998708 2.2
C529 crystal glass 15.29154528 38.18790483 3.8
C530 crystal glass 5.67437413 35.63187344 2.6
C531 crystal glass 3 19.84358278 1.8
C532 crystal glass 4.935711247 24.9788656 2.119275659
C533 crystal glass 3.063330747 27.94495885 1.481705795
C534 crystal glass 4.469990657 38.36365959 0.3
C535 crystal glass 3.707322304 43.58876255 2.8
C536 crystal glass 8 35.50421682 2
C537 crystal glass 8.040393521 45.11012695 2.229345482
C538 crystal glass 7.033910407 33.08836527 2.350078597
C539 crystal glass 8.837084711 29.52140461 1.558601151
C540 crystal glass 6.293678951 38.92805758 1.310880774
C541 crystal glass 1 32.23978263 2.892660012
C542 crystal glass 11 49.35094729 3.2
C543 crystal glass 11 32 2.454768845
C544 crystal glass 3.168462963 42.46744799 1.03468882
C545 crystal glass 6.554210304 33.27253443 2.500814712
C546 crystal glass 8.470654339 35.23297805 2
C547 crystal glass 7.811836103 32.92559527 1.114276207
C548 crystal glass 6.230743744 51.72123031 3
C549 crystal glass 2.371707754 39.50219674 1.666117373
C550 crystal glass 1 40.16428368 0.507681884
C551 crystal glass 9.45517513 49.94000125 1.90603166
C552 crystal glass 7 36.39015164 1.904389365
C553 crystal glass 16.39833217 61 4.7
C554 crystal glass 10.9239396 40.55633376 1.029520086
C555 crystal glass 13.01190473 48 4.1
C556 crystal glass 7.14970634 31.43611225 1.661941931
C557 crystal glass 11.59505127 37.73546348 2.4
C558 crystal glass 0.887796923 41.67246546 0.827883978