Research Design Bias

Information Bias

caused by: 1.) Memory(recall bias, ie can't remember) 2.) Communication 3.) Knowledge 4.) Moivation 5.) Social Desirability 6.) Response set 7.) Threatening or personal questions

What's Selection Bias

which may result in the subjects in the sample being unrepresentative of the population of interest . Selection biases occur when the groups to be compared are different. These differences may influence the outcome

How do selection Bias arise?

1.) Choice of sampling frame 2.) Non response: refusal, un reachable, to ill to be intreviewed, unable to complete the interview 3.) Self Selection (Volunteer vs referrals)

What are sources of bias in cohort studies?

1.0 Selection Bias-non participation, loss to follow up 2.) Information Bias-ascertainment disease is pursued more vigorously in one group than in another. and when individuals are misclassified on exposure or on disease

Sources of bias in Case-Control studies

Inclusion of cases or controls into the study depends in someway upon the exposure of interest. Choice of sampling frame, non response, self selection, selective survival.

Insensitive measure bias

Insensitive measure bias occurs when the measurement tool(s) used are not sensitive enough to detect what might be important differences in the variable of interest.

Instrument bias

Instrument bias occurs when calibration errors lead to inaccurate measurements being recorded, e.g., an unbalanced weight scale.

What are intervention Biases?

Intervention or exposure biases generally are associated with research that compares groups. Common intervention biases include: contamination bias, co-intervention bias, timing bias(es), compliance bias, withdrawal bias, and proficiency bias.

What happens if you have a Bias

It threatens validity of your study results

Measurement Bias

Measurement biases involve systematic error that can occur in collecting relevant data. Common measurement biases include instrument bias, insensitive measure bias, expectation bias , recall or memory bias, attention bias, and verification or work-up bias.

What are The three main types of Bias

Misclassification, Selection, and information/recall

Nonrespondentbias

Nonrespondent bias occurs when those who do not respond to a survey differ in important ways from those who respond or participate. This bias can work in either direction.

Vounteer/Referral Bias

Occurs when volunteers are more willing to participate in the study than referral. Volunteer or referral bias occurs because people who volunteer to participate in a study (or who are referred to it) are often different than non-volunteers/non-referrals. This bias usually, but not always, favors the treatment group, as volunteers tend to be more motivated and concerned about their health.

Proficiency bias.

Proficiency bias occurs when the interventions or treatments are not applied equally to subjects. This may be due to skill or training differences among personnel and/or differences in resources or procedures used at different sites.

Recall or memory bias

Recall or memory bias can be a problem if outcomes being measured require that subjects recall past events. Often a person recalls positive events more than negative ones. Alternatively, certain subjects may be questioned more vigorously than others, thereby improving their recollections.

What's Bias

Systematic error in collectin or interpreting data

Attention bias

Attention bias occurs because people who are part of a study are usually aware of their involvement, and as a result of the attention received may give more favorable responses or perform better than people who are unaware of the study's intent.

Co-intervention bias

Co-intervention bias occurs when some subjects are receiving other (unaccounted for) interventions at the same time as the study treatment...2x intervention, let's say given the treatment twice

Compliance bias.

Compliance bias occurs when differences in subject adherence to the planned treatment regimen or intervention affect the study outcomes

Contamination bias.

Contamination bias occurs when members of the 'control' group inadvertently receive the treatment or are exposed to the intervention, thus potentially minimizing the difference in outcomes between the two groups.

Timing bias(es

Different issues related to the timing of intervention can cause bias. If an intervention is provided over a long period of time, maturation alone could be the cause for improvement. If treatment is very short in duration, there may not have been sufficient time for a noticeable effect in the outcomes of interest.

Expectation bias

Expectation bias occurs in the absence of masking or blinding, when observers may err in measuring data toward the expected outcome. This bias usually favors the treatment group

Verification or work-up bias

Verification or work-up bias is associated mainly with test validation studies. In these cases, if the sample used to assess a measurement tool (e.g., diagnostic test) is restricted only to who have the condition of factor being measured, the sensitivity of the measure can be overestimated.

Withdrawal bias

Withdrawal bias occurs when subjects who leave the study (drop-outs) differ significantly from those that remain