How to Display Data- P15

How to Display Data- P15:The best method to convey a message from a piece of research in health isvia a fi gure. The best advice that a statistician can give a researcher is to fi rstplot the data. Despite this, conventional statistics textbooks give only briefdetails on how to draw fi gures and display data.
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How to Display Data- P1562 How to Display Data Table 6.2 Self-reported birthweight (kilograms) by delivery type, n 3178 women4 What kind of delivery? Birthweight (kg) Mean (SD) n Forceps delivery 3.46 (0.53) 88 Ventouse (vacuum extractor) 3.44 (0.50) 209 Normal vaginal delivery 3.41 (0.52) 2190 Emergency caesarean section 3.36 (0.70) 426 Planned caesarean section 3.29 (0.59) 249 Vaginal breech delivery 2.81 (0.70) 16 Total 3.39 (0.55) 3178first. The table has a title explaining what is being displayed and the col-umns and rows are clearly labelled. As with Table 6.1, the sample size foreach delivery type group is reported in the final column of the table as thisimproves the understanding of data. It is good practice to put the variablesof most interest, in this table the mean and SD, in the first data column asthey can be immediately read with their associated group label. In many studies, comparisons are made between different groups. Forexample, two groups of patients may be given different treatments and theoutcomes compared between these treatment groups. Table 6.3 shows anexample of a more complex table with three variables: birthweight (the out-come variable in this case); and two categorical variables or factors: parityTable 6.3 Self-reported birthweight (kg) by delivery type and parity, n 3176women4What kind of delivery? Primiparous Multiparous birthweight (kg) birthweight (kg) Mean (SD) n Mean (SD) nForceps delivery 3.43 (0.54) 75 3.68 (0.44) 13Emergency caesarean section 3.40 (0.67) 299 3.27 (0.77) 127 (once labour had started)Ventouse (vacuum extractor) 3.37 (0.47) 161 3.66 (0.53) 48Normal vaginal delivery 3.30 (0.51) 847 3.48 (0.50) 1341Planned caesarean section 3.15 (0.65) 70 3.35 (0.57) 179Vaginal breech delivery 3.02 (0.54) 7 2.64 (0.80) 9Total 3.32 (0.56) 1459 3.45 (0.54) 1717 Data in tables 63and delivery type. The outcome, birthweight, is cross classified by parity anddelivery type. In this example delivery is ordered by the combined samplesize for each delivery type.6.4 Tables for multiple outcome measuresThe use of health-related quality of life (HRQoL) measures is becomingmore frequent in clinical trials and health services research, both as primaryand secondary outcomes. It is typically assessed by a self-completed ques-tionnaire which asks a series of standardised questions about various aspectsor facets of a person’s HRQoL. The Medical Outcomes Study 36-Item ShortForm (SF-36) is the most commonly used HRQoL measure in the worldtoday.7,8 It contains 36 questions measuring health across eight dimensions:physical functioning (PF); role limitation because of physical health (RP);social functioning (SF); vitality (VT); bodily pain (BP); mental health (MH);role limitation because of emotional problems (RE) and general health (GH).These eight dimensions are usually regarded as a continuous outcome andare scored on a 0–100 scale, where 100 indicates ‘good health’. Table 6.4 shows SF-36 data from a postal survey of all patients aged 65years or over registered with 12 general practices. The survey aimed toassess the practicality and validity of using the SF-36 in a community-dwell-ing population over 65 years old, and obtain population scores in this agegroup.9 The table displays summary statistics (mean, SD and sample size) forthe eight main dimensions of the SF-36. The columns contain the ordered age categories and the rows contain theeight SF-36 dimensions. The column variable, age, has a natural ordering sothe columns are clearly ordered by the age categories: the row variables (theeight SF-36 dimensions) have no natural ordering, in this example they areordered by the dimension with the highest overall mean score (social func-tion). The footnote to the table also explains how the SF-36 is scaled. Theunits and scale of HRQoL may be unfamiliar to many readers (unlike otheroutcomes such as birthweight) and the footnote helps in the understandingand interpretation of the mean SF-36 dimension scores. Most HRQoL meas-ures generate a scale or scores that have no natural units and have varyingscale ranges: for som ...