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Hello, and welcome to module five.

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Now that we've reviewed
our epi study designs,

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measures of disease
frequency and association,

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and some of the inferential statistics,

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we're going to turn our attention

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to threats to internal validity.

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This is what we'll be spending pretty much

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the rest of the course talking about.

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If you remember back to epi one,

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threats to internal validity
include things like bias,

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confounding, effect
modification, or interaction,

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and also random chance.

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We'll start here in module
five talking about bias.

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Remember that bias is
inherent in study designs.

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It's not something that we
can control or adjust for

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in our analysis after
the study is complete,

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which means that we need
to be really careful

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in our study design to minimize bias

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as much as we possibly can.

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If you have questions on this material,

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or need support in any
way, please reach out.