Evidence Based Medicine
Study Methodology
Which of the following best describes an intention to treat analysis:
Answer:
An intention to treat (ITT) analysis is one in which all patients are included in the analysis, classified according to the group into which they were randomised, even if they were withdrawn from the study and did not actually receive the treatment, did not comply with treatment or drop-out. Intention to treat analysis is a more reliable estimate of true treatment effectiveness by replicating what happens in the ‘real world’ (e.g. noncompliance and protocol violations commonly affect therapies).Interventional Trials
Evidence Based Medicine / Study Methodology
Last Updated: 21st April 2019
Interventional trials are used to test a hypothesis that a particular healthcare intervention is different from another, or from no intervention. Interventional studies provide the most convincing evidence for any hypothesis as it is generally possible to control for confounding factors that may affect outcome. Randomised control trials (RCTs) are the gold standard for studying treatment effects, providing a reliable measure of efficacy and allowing for meta-analysis but they are difficult, time-consuming and expensive to set up. There can also be ethical problems in giving different treatments to two groups.
Phases
- Phase I: the first stage of human testing where a small group of healthy volunteers is given the intervention under close monitoring to evaluate safety, tolerability and pharmacodynamics
- Phase II: larger trials in both healthy volunteers and patients in which safety and tolerability continue to be assessed, but efficacy is also evaluated
- Phase III: even larger multicentre randomised controlled trials (RCTs) to definitively assess efficacy against the gold standard, interventions with satisfactory results will get marketing authorisation
- Phase IV: post-marketing surveillance trials in which safety data continue to be collected, and specific issues, such as drug interactions and pregnancy may be evaluated, even after the intervention is licensed
The sample size in a phase II or III clinical trial is critical and must be determined knowing the incidence of the disease in question, the potential effect of the intervention (estimated from earlier studies), the significance level deemed acceptable, and the variance of the outcome measure.
Randomisation
Randomisation to study groups removes any allocation bias. It also may improve the chance of having comparably matched groups by randomly distributing confounding variables between the treatment arms, depending on the randomisation strategy.
Blinding
- Open trial: everybody knows which intervention is being given.
- Single blind trial: either the subject or the researcher is not blinded. This is usually either because the placebo does not perfectly mimic the intervention, or because the researcher has to know the full facts.
- Double blind: both the subject and researcher are blinded. This usually achieves the highest standard of scientific rigor.
Cross-Over Study
Each patient receives both (or all) of the interventions being compared, and therefore acts as their own control (although comparison takes place at different time points). The order in which they receive the interventions must be randomised and there is usually a 'washout period' between different drugs. This is only suitable for chronic disease that is not curable but for which treatment may give short-lived, temporary relief. Fewer patients are required because many between-patient confounders are removed, thus they are often used to study rare diseases.
Follow-Up
The follow-up period must be long enough to allow outcomes of the trial to occur, which requires prior knowledge about the natural history of the condition being studied. Drop-out rates must be sufficiently low so as not to bring into doubt the results of the trial.
An intention to treat (ITT) analysis is one in which all patients are included in the analysis, classified according to the group into which they were randomised, even if they were withdrawn from the study and did not actually receive the treatment, did not comply with treatment or drop-out. Intention to treat analysis is a more reliable estimate of true treatment effectiveness by replicating what happens in the ‘real world’ (e.g. noncompliance and protocol violations commonly affect therapies).
This type of analysis is in contrast to ‘per protocol’ analysis (where analysis includes only those patients who completed the treatment originally allocated) and ‘as treated’ analysis (where analysis classifies patients based on the actual treatment they received and not the treatment they were originally allocated to).
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
