What is bias? What are three types of bias? is any factor or process that tends to deviate the results or conclusions of a “Bias systematically away from the truth.” Sackett Three types of bias: Selection bias the outcomes of a trial are affected by systematic differences in the – “when way in which individuals are accepted or rejected for a trial or in the way in which the interventions are assigned to individuals once they have been accepted into a trial” Jadad Ascertainment bias when the results or conclusions of a trial are systematically – “occurs distorted by knowledge of which intervention each participant is receiving” Jadad Missing data bias occurs when participants are lost to follow-up, drop out of the or – there are deviations from the protocol so data is not collected at appropriate time points. Publication bias propensity for investigators and sponsors to and submit, and for – “a peer-reviewers and editors to accept, manuscripts for publication depending on the direction of the findings.” Jadad i.e. Positive results are more likely to be published. What selection bias is apparent in this study? Allocation bias - not all participants in the study were given an equal opportunity to receive the intervention under study. In this trial, the weekly blocks were assigned randomly but individual patients within the blocks did not all receive or not receive the intervention. There was no blinding and individual clinicians determined which patients presenting during the POC testing weeks received the intervention. What is allocation concealment? Allocation concealment is procedure for protecting the randomisation process so that “the the treatment to be allocated is not known before the patient is entered into the study”, Forder For example: by sequentially numbered, opaque, sealed envelopes or by off-site assignment of randomisation. Have the investigators taken any steps to control for selection bias?
What is bias? What are three types of bias? “Bias is any factor or process that tends to deviate the results or conclusions of a systematically away from the truth.” Sackett Three types of bias: Selection bias – “when the outcomes of a trial are affected by systematic differences in the way in which individuals are accepted or rejected for a trial or in the way in which the interventions are assigned to individuals once they have been accepted into a trial” Jadad Ascertainment bias – “occurs when the results or conclusions of a trial are systematically distorted by knowledge of which intervention each participant is receiving” Jadad Missing data bias – occurs when participants are lost to follow-up, drop out of the or there are deviations from the protocol so data is not collected at appropriate time points. Publication bias – “a propensity for investigators and sponsors to and submit, and for peer-reviewers and editors to accept, manuscripts for publication depending on the direction of the findings.” Jadad i.e. Positive results are more likely to be published. What selection bias is apparent in this study? Allocation bias - not all participants in the study were given an equal opportunity to receive the intervention under study. In this trial, the weekly blocks were assigned randomly but individual patients within the blocks did not all receive or not receive the intervention. There was no blinding and individual clinicians determined which patients presenting during the POC testing weeks received the intervention. What is allocation concealment? Allocation concealment is “the procedure for protecting the randomisation process so that the treatment to be allocated is not known before the patient is entered into the study”, Forder For example: by sequentially numbered, opaque, sealed envelopes or by off-site assignment of randomisation. Have the investigators taken any steps to control for selection bias?
110720a_-_point_of_care_troponin_in_ed_loten_-_emj_2011.docx