Confounding is an important concept in epidemiology, because,
if present, it can cause an over- or under- estimate of the observed association between exposure and health outcome
. The distortion introduced by a confounding factor can be large, and it can even change the apparent direction of an effect.
Why are confounding factors important?
Confounding variables are those
that may compete with the exposure of interest
(eg, treatment) in explaining the outcome of a study. The amount of association “above and beyond” that which can be explained by confounding factors provides a more appropriate estimate of the true association which is due to the exposure.
Why does confounding occur?
In order for confounding to occur,
the extraneous factor must be associated with both the primary exposure of interest and the disease outcome of interest
.
What do confounders do?
A confounding variable, also called a confounder or confounding factor, is
a third variable in a study examining a potential cause-and-effect relationship
. … It can be difficult to separate the true effect of the independent variable from the effect of the confounding variable.
What are the characteristics of confounding?
In order for a variable to be a potential confounder, it needs to have the following three properties: (1)
the variable must have an association with the disease, that is, it should be a risk factor for the disease
; (2) it must be associated with the exposure, that is, it must be unequally distributed between the …
How do you know if confounding is present?
Identifying Confounding
In other words, compute the measure of association both before and after adjusting for a potential confounding factor.
If the difference between the two measures of association is 10% or more, then confounding was present
. If it is less than 10%, then there was little, if any, confounding.
How can we reduce confounding?
- randomization (aim is random distribution of confounders between study groups)
- restriction (restrict entry to study of individuals with confounding factors – risks bias in itself)
- matching (of individuals or groups, aim for equal distribution of confounders)
What confounding means?
Confounding means
the distortion of the association between the independent and dependent variables
because a third variable is independently associated with both. A causal relationship between two variables is often described as the way in which the independent variable affects the dependent variable.
What’s an example of confounding?
A confounding variable is an
“extra” variable that you didn’t account for
. They can ruin an experiment and give you useless results. … For example, if you are researching whether lack of exercise leads to weight gain, then lack of exercise is your independent variable and weight gain is your dependent variable.
Is time a confounding variable?
Here, we consider “time-modified confounding,” which occurs when there is a
time-fixed or time-varying cause of disease
that also affects subsequent treatment, but where the effect of this confounder on either the treatment or outcome changes over time.
Are risk factors confounders?
A confounder is
a factor that is related to the risk factor of interest
and, independently of this, to outcome (disease status), but is not an intermediate factor on the causal path between the risk factor and outcome (see, for example, Rothman and Greenland [7]).
What problems can confounding variables cause?
What problems can confounding variables cause?
They can cause the study to favor certain results unexpectedly
. They can cause incorrect conclusions to be drawn from the study.
Does blinding reduce confounding?
The purpose of blinding is
to minimise bias
. … Random assignment of participants to the different groups only helps to eliminate confounding variables present at the time of randomisation, thereby reducing selection bias. It does not, however, prevent differences from developing between the groups afterwards.
What happens when we ignore confounding?
Ignoring confounding when assessing the associ- ation between an exposure and an outcome variable can lead to
an over- estimate or underestimate of the true association between exposure and outcome
and can even change the direction of the observed effect.
What is positive confounding?
Confounding. A situation in which the effect or association between an exposure and outcome is distorted by the presence of another variable. Positive confounding (
when the observed association is biased away from the null
) and negative confounding (when the observed association is biased toward the null) both occur.
Is smoking a confounder?
Cigarette smoking is
a potential confounder of the relationship between obesity and mortality
, and statistical control for this factor requires careful consideration.
