Statistical methods
Descriptive epidemiology for each group as defined by pattern of ALF testing will include analysis of continuous and categorical data on subject characteristics using χ2 tests for categorical variables and by t-tests for continuous variables or non-parametric equivalents.
For the baseline population, liver function tests will be extracted and number and frequency tabulated by year. The 'liver function tests' will be:
Liver function
• Bilirubin
• Albumin
Liver damage
• Alkaline phosphatase (Alk Phos)
• Gamma-glutamyl transferase (GGT)
• Alanine transaminase (ALT)
• Aspartate aminotransferase (AST)(not routinely measured)
Normal and abnormal (and possibly mildly abnormal) categories will be defined for each test using regional laboratory standard cut-offs which vary by age and sex for some tests (table 1). Sensitivity analyses will be performed for some tests (eg ALT where mild abnormality or top quartile in Normal range may be a useful category for prediction.)
Table 1  Liver function tests and definitions of abnormal   Categories of patterns of tests will be defined. For example the following may be possible:
1. Raised ALT + normal Alk Phos + normal GGT (suggesting hepatitis)
2. Raised Alk Phos +/- raised GGT + normal ALT (suggesting biliary cirrhosis)
3. Any one abnormal
4. Any 2 or more abnormal and/or explore patterns.
Patterns of repeat tests will also be explored. The main outcomes and covariates will be tabulated by initial and repeat LFT patterns (Rates presented as events per thousand person years).
Sensitivity, specificity, positive predictive value and likelihood ratios will be calculated for LFT patterns compared with actual outcome. Kaplan-Meier plots of time to outcomes will be plotted for patterns of tests and individual tests above.