Bias

Question 1

Berkson’s bias (aka admission rate bias)

Answer 1

A form of selection bias that causes hospital cases and controls in a case control study to be systematically different from one another because the combination of exposure to risk and occurrence of disease increases the likelihood of being admitted to the hospital. Berkson’s bias (aka admission rate bias): This is a type of bias resulting from case-control studies whereby cases and controls are selected from hospital settings. In such settings, cases can be unrepresentative of the general population and this can lead to confounding factors.

Question 2

Neyman bias

Answer 2

Neyman Bias is a selection bias where the very sick or very well (or both) are erroneously excluded from a study. The bias (“error”) in your results can be skewed in two directions: Excluding patients who have died will make conditions look less severe.

Question 3

Publication bias

Answer 3

Publication bias occurs when important evidence has failed to be considered. Funnel plots can be used to check for this.

Question 4

Selection bias

Answer 4

(when selected sample is not a representative sample of reference population

Question 5

Subtypes of selection bias

Answer 5

Loss to follow up bias, disease spectrum bias, self selection bias, participation bias, incidence prevalence bias, exclusion bias, publication of dissemination bias, citation bias, berkson’s bias

Question 6

Subtypes of information bias

Answer 6

Detection bias, recall bias, lead time bias, interviewer/observer bias, verification and workup bias, Hawthorne effect, ecological fallacy

Question 7

Disease spectrum bias (aka case mix bias)

Answer 7

this can occur when a treatment is studied in more sever forms of a disease. Such results may then not apply to mild forms of the disease.

Question 8

Self selection bias

Answer 8

Those who volunteer may have shared characteristics resulting in a unrepresentative sample.

Question 9

Participation bias (non-response bias)

Answer 9

Those who participate may have shared characteristics resulting in a unrepresentative sample.

Question 10

Incidence prevelance bias

Answer 10

Incidence-Prevalence bias (Survival bias, Neyman bias): Occurs in case-control studies and is attributed to selective survival among the prevalent cases (i.e. mild, clinically resolved, or fatal cases being excluded from the case group).

Question 11

Exclusion bias

Answer 11

Occurs when certain patients are excluded for example if they are considered ineligible

Question 12

Publication bias

Answer 12

Many studies may not be published. This may be due to the fact that papers with positive results, and large sample sizes are more likely to get published.

Question 13

Citation bias

Answer 13

Articles of high citation are easy to reach and have higher chance to be entered into a given study

Question 14

Information bias

Answer 14

when gathered information about exposure, outcome or both is not correct and there was an error in measurement )

Question 15

Detection bias

Answer 15

This can occur when exposure can influence diagnosis. For example women taking an oral contraceptive will have more frequent cervical smears than women who are not on the pill and so are more likely to have cervical cancer diagnosed (if they actually have it). Thus, in a case-control study that compared women with cervical cancer and a control group, at least part of any higher pill consumption rates amongst the former group may be due to this effect.

Question 16

Recall bias/information bias

Answer 16

In retrospective studies that participants should remember and determine their past exposure, it is likely to have cases and controls that do not act similarly in this regard. To better put, because of more reflection on reasons of disease it is likely to have cases that do recall and cite better the detailed conditions of their exposure than controls

Question 17

Lead time bias

Answer 17

Lead time is the period between early detection of disease and the time of its usual clinical presentation. When evaluating the effectiveness of the early detection and treatment of a condition, the lead time must be subtracted from the overall survival time of screened patients to avoid lead time bias. Otherwise early detection merely increases the duration of the patients’ awareness of their disease without reducing their mortality or morbidity. Numerous cancer screening procedures were thought to improve survival until lead time bias was addressed

Question 18

Interviewer/observer bias

Answer 18

Interviewer or observer knowledge about in-question hypothesis and disease or/and exposure can take effect on collection and registry of data

Question 19

Verification and work up bias

Answer 19

This is a type of bias in which the results of a diagnostic test affect whether the gold standard procedure is used to verify the test result. It is more likely to occur when a preliminary diagnostic test is negative because many gold standard tests can be invasive, expensive, and carry a higher risk.

Question 20

Hawthorn effect

Answer 20

This can occur when participants alter their usual behaviour due to their awareness that they are being studied

Question 21

Ecological fallacy

Answer 21

This can occur when conclusions about individuals are based only on analyses of group data.

Question 22

Which of the following is the best measure of internal consistency?

Answer 22

Internal consistency is the extent to which items on a test measure various aspects of the same characteristic and nothing else.

There are four main ways to assess it:-

Average inter-item correlation
Average item-total correlation
Split half correlation
Cronbach’s alpha

Question 23

Pygmalion effect/experimenter expectancy effect

Answer 23

The Pygmalion effect, or Rosenthal effect, is the phenomenon whereby higher expectations lead to an increase in performance. The effect is named after the Greek myth of Pygmalion, a sculptor who fell in love with a statue he had carved, or alternately, after the Rosenthal–Jacobson study (see below).

Question 24

Resources re:bias

Answer 24

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.610.8597&rep=rep1&type=pdf

Question 25

Ascertaining bias

Answer 25

Ascertainment bias is a systematic distortion in measuring the true frequency of a phenomenon due to the way in which the data are collected. In genetics, ascertainment bias is an important factor in the use of family pedigree data to establish modes of inheritance.

Question 26

Surveillance bias

Answer 26

Also called detection bias, occurs when one group is followed more closely than the other group. This could lead to an outcome being diagnosed more often in the more closely followed group