Reducing bias: Blinding


-Double blinding

-Single blinding


Definition: “blinding is the process of concealing info. from participants (sometimes including researchers) about which individulas recieve which treatments”

Rarely done – but probably should be - in ecology!

Particularly a problem when data arecollected

-subjectively: “lemur A made 3 aggressive actions toward lemur B”

-visually: % cover, % leaf damage

-Don’t worry about collecting blinded data

-BUT you should consider

-How bias could creep into your results

-If your study might be particularly susceptible to bias





























A common ecological metric that is subjective:

-Percent cover of vegetation

-How might this be biased in an experiment?





























Blinding is rare - but it does impact conclusions!

Blinding





























Aside: what are “recognization studies” in behavioral ecology? “recognition studies typically perform intra- and inter colony aggression assays, with the a priori expectation that there should be little or no aggression among nestmates. Aggressive interactions between ants can include subtle behaviours such as mandible flaring and recoil, which can be hard to quantify, making these types of assays prone to confirmation bias.” “Confirmation Bias in Studies of Nestmate Recognition: A Cautionary Note for Research into the Behaviour of Animals” PLOS 1





























How to reduce the influence of sampling error (14.4)

-Sampling error = noise

-more noise = larger standard deviation / stand. error

-harder to detect …

-differences between groups,

Sampling error “reduces power”

Best solution

-collect more independent samples





























Statistical “Power”

-“Power” is the ability to detect a difference between groups or a trend when it is actually there

-A large sample size increases power

-A large difference between groups / steep trend essentialy increases power

(but you don’t have control over this)

-Study design / stat. procedures can increase power





























Reducing sampling error: Replication

Definition:

Replication is the application of every treatment to multiple, INDEPENDENT experimental units."





























Reducing sampling error: Balance

Definition: “balanced experiments have equal sample sizes” (pg 434)

-lack of balance reduces power

-or, “unbalanced experiments have lower power”

-observational studies usually unbalanced (such is life)

-doing extra work to increase balance can be beneficial

A random & balanced experiment





























AN UNbalanced experiment

Test-ish question: “What is the effect of balanced on an experiment?”