Critical Appraisal Series

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1 Definition for therapeutic study Terms Definitions Study design section Observational descriptive studies Observational analytical studies Experimental studies Pragmatic trial Cluster trial Researcher observed and report one participant or a group of patients without any control gorup. i.e. case report / cases series Researcher report similarities and differences observed between 2 or more group of participants Researcher intervenes with the treatment under investigation to one group and treat the other group with another treatment, mostly conventional treatment, placebo, or no intervention, the outcome difference in outcome will be studied. Pragmatic trial is designed to measure the effectiveness of the intervention. The trial is carried out in an ordinary clinical situation which the result is more reflective of the daily practice. Participants re randomly assigned as a cluster or group instead of as individuals. This tends to be use for evaluating the delivery of health services. [see cluster sampling] Method section Target population Sample population Random sampling Stratified sampling Cluster sampling Convenience sampling Inclusion & exclusion criteria Target population is the population of interest set by the research. This population is screened by investigator in order to identify the target population Sample population is selected from target population by by the study inclusion and exclusion criteria. Every participant in the target population has been selected by equal chance. The target population is divided into 2 or more subgroup or strata based on its characteristic [confounder] and randomly sample from each strata. Its aim is to equally spread the confounder among the groups in order to avoid hidden confounder or biases. The target population is divided into cluster i.e. centre 1 vs centre 2 or one ambulance service vs another one. The sampling is recruited randomly from these clusters. The target population is sampled as convenient. Convenice sampling is easiest and potentially most dangerous for biases. Good results often obtained but with potential bias. A set of criteria which is set by the researcher in order to select the sample population. This would be a key assessment for diagnostic purity bias and the generalisability of the trial result. The study internal validity and generalisability are often a trade off. Dr J Leung Page 1 of 7 Definition for therapeutic study

2 Internal validity External validity Concealed allocation Randomisation Block randomisation Whether the study method permits the result to be a reflection of the truth - i.e. can it trust the result presented? Can the study result be extrapolated to a wider population? - i.e. generalisability Key assessment - target population selection and setting of the study The researcher does not know which group the participant is being allocated when recruited and before randomisation. It is different from different to blinding as it occur prior to randomisation. The method to achieve concealed allocation can be achieved by the following method:- - Centralised concealment scheme Clinician check eligibility, gain consent, decides on enrolment - then finally contact the centre for randomisation to determine group allocation. Purpose is to prevent selection bias which can compromise the randomisation process. The trial participants are randomly allocated to in each group in order to equally spread the confounders and characteristic among the study group. Simple randomisation would sometime results in unequal number of confounders especially in a small number of participant. It is design to allow equal number in each study group. Stratified block randomisation Cluster randomisation Adaptive randomisation Quasi-randomisation A process designed to allocated participant into different block according to their known confounder i.e. gender. Block randomisation occur among the stratified group. This will result in equal number of known confounder spread among the study groups in order to minimize the effect of confounder. Randomisation applied to a group/cluster of participant i.e. patient recruited via London ambulance service would receive treatment X and East of England ambulance would receive treatment Y etc. Participant is allocated into different group using probability in order to achieve similar number in each group with similar characteristic. It is a superior randomisation method to equally distribute the confounder. The participant is randomised according to certain characteristic i.e. when certain clinician is on duty Vs other clinician or time of the day [ 9:00-17:00 in one group and out of hours in another] This is an inferior method of randomisation. Dr J Leung Page 2 of 7 Definition for therapeutic study

3 Blinding Open trial It is a method which ensure either the researcher, participant or the analyst are blinded to the intervention that the participant is receiving in order to prevent selection, observational and analytical bias. Blinding occurs after randomisation. No blinding occur Single blind Double blind Triple blind Difficulty of blinding Placebo Placebo effect Double dummies Intention to treat analysis Follow-up Effectiveness The participants or researcher are blinded to their intervention allocation. The patient and the researcher are blinded to the intervention or control groups allocation The participants, researcher and the analyst are all blinded to the allocated group until the end of the trial result analysis. Blinding can sometime be difficult to be achieved due to the nature of the intervention i.e. EGDT Vs conventional treatment for sepsis. However, a good methodology would ensure analyst are blinded to the allocated groups. The use of dummy drug as a control treatment. The dummy drug should ideally be as similar to the treatment as possible. Placebo should have all the components of the investigating treatment except the active component of the drug. Placebo is now rarely used due to ethnical consideration. It is the improvement of outcome observed in the placebo group. The use of 'Hard' primary outcome tends to be less affected by placebo effect. The participant would appear to receive both treatment together with either of the active component of control and intervention treatment in the drug. This is a superior method to reduce the placebo effect. Downside of this is very expensive to run. Patient is always analysed in the group that they were randomised, regardless of what treatment they actually received. This can avoid the possible of attrition bias. [Drop out bias] The length of follow up always need to consider in critical appraisal if a short follow up can lead to the miss out of the outcome effect A high postal questionnaire response rate can indicate the cohort is a highly selected patient group. The effect of the treatment in a ordinary clinical condition. Its outcome result tends to be less impressive compare with the efficacy data. Dr J Leung Page 3 of 7 Definition for therapeutic study

4 Efficacy Subjective 'Hard' outcome Patient - centred outcome Surrogate outcome The treatment efficacy is investigated in an ideal condition. i.e. phase III trial of treatment. The treatment effect tends to be more impressive than effectiveness of treatment Outcome measure is subjective i.e. mortality or M.I recurrence Outcome measures which patient care about. i.e. quality of life. As It is a soft' outcome and objective, it is prior to observational bias. These outcomes are an indirect measurement of the hard outcome. i.e. BP measurement or ICP measurement. Tends to be less valid and poor clinical significant compare with subjective outcome like mortality. Validity Section Validity Bias Selection bias Observation bias Hawthorne effect Confounding Chance Is the finding true? - have they measured what they supposed to? Systemic error occurs as a result of how observation was made or experiment was carried out which lead to inaccurate estimate. Bias is avoidable. The selection of sample is not properly randomised, hence sample obtained is not a true representative of the population intended to be studied. Bias introduced into studies when the method of observation used causes the result to be skewed in some non-random manner, leading to inaccurate results. People behave differently as they are being observe which can potentially introduce observational bias into the study. Confounding is an error of interpretation. The results of the study may be precise and accurate, but they are misinterpreted and a false conclusion is drawn. Random error/variation which leads to imprecision. Power The likelihood of detecting a true difference. It is also the probability of rejecting the null hypothesis. The power of a study is defined as 1-beta. Conventionally, a study should aim to recruit a sufficient sample size for the power to be 80 or 90%. Several factors will influence study power: Level at which alpha is set 0.05 by convention Sample size Variability of the outcome measure (defined by its standard deviation) The minimum clinically significant difference we wish to detect Dr J Leung Page 4 of 7 Definition for therapeutic study

5 Accuracy Precision Type 1 error Type 2 error External validity Jadad score This describe how close an estimate is to true value. An inaccurate estimate will differ from the true value because bias has led to a systematic error in the estimate. P-value Precision describes how close an estimate is to true value. Imprecision estimate will differ from the true value because random variation has led to a random error [chance] in the estimate. The trial estimate have rejected the null hypothesis when it is true [false-positive result] The trial estimate have accepted the null hypothesis when it is false. [False -negative result] it is whether the study result is generalisable to a wider population outside the study. it is a methodological way to assess the quality of the trial [ usually a RCT] and allocate a score to each component of the trial. Questions:- 1) Was the study randomised?[1point] 2) Was the study double blind?[1point] 3) Was there a description of withdrawal or drop out? [1point] 4) randomisation appropriate? [1 point] 5) blinding= appropriate? [1 pont] Point =deduced:- a) Random = described but inappropriate b) Blinding = inappropriate Result & statistic section Experimental Event rate [EER] Control Event rate [CER] Absolute risk reduction [ ARR] Relative risk [RR] Relative risk reduction Rate of worst primary outcome event in the experimental treatment group. [No. of Treated patient with primary outcome / Total No. of treated patient.] EER= a/(a+b) Rate of worst primary outcome event in the control group. [No. of patient in the control group with primary outcome / Total No. of tpatint in the control group.] CER= c/(c+d) The absolute different in event rate between the control group and the experimental group. ARR=CER-EER The relative risk between the experimental group and the control group. RR= EER/CER The absolute difference between the control group and the experimental group divided by the control event rate RRR = (CER-EER)/CER Dr J Leung Page 5 of 7 Definition for therapeutic study

6 Number needed to treat [NNT] Odds Odd ratio Mean Median Mode The number of people who have been given the allocated treatment to generate one positive outcome. NNT = 1/AAR A way of describing risks. Odds is calculated by the number of events divided by the number of non-event. [a/b or c/d] The odd from the treated group divided by the control group. RR depends on baseline event rate and prevalence but odd ratio os not affected OR is not affected by prevalence. The sum of the values divided by the number of values The middle number of the group when the values are ranked in order. - if there is an even amount of values then the mean number of the two middle values is taken. - Median is used in skewed value in order to reduce the effect of outliers. The most frequently occuring number in a list. Mode is mostly used to describe non-numerical data [ e.g. ethnic group] Inter quartile range IQS - measure for the spread of the data. It is the difference between the lower and the upper quartiles, which included middle 50% of the sample data. It is used to lessen the effect of the outliers in a skewed data set. Quartiles are values that divided sample data into 4 equal numbers of observations. P-value Paired data The probability of that the null hypothesis is true. The lower the p-value is less likely that the result is due to chance. Conventional p-value cut-off is 0.05 in order to claim the result to be statistical significant. Dataset is collected in same individual with a different time point. Unpaired data Dataset is collected from two or more different groups of patient cohort. It is known as independent data' Dr J Leung Page 6 of 7 Definition for therapeutic study

7 Worst outcome Worst outcome Positive negative Total Experiment a b a+b Control c d c+d Total a+c b+d a+b+c+d CER EER ARR Relative risk Relative risk reduction NNT Odds of outcome in experimental group Odds of outcome in control Odds ratio c / (c+d) a / (a+b) CER-EER EER/CER ARR/ CER 1/ ARR a / b c / d ad/bc [ (a/b) / (c/d) Dr J Leung Page 7 of 7 Definition for therapeutic study

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