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<v ->Welcome to Module 9.</v>

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This module starts our discussion of effect modification

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which is also called interaction or moderation.

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You'll hear those terms used interchangeably

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throughout this module and in epidemiology in general.

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If we take a step back,

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we've been talking about threats to internal validity

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in EPI studies since Module 5.

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We started out with bias

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and then we spent three modules talking about confounding.

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We'll spend the next three modules

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talking about effect modification using the same structure.

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We'll start here in module 9,

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going over the theoretical

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and conceptual framework of effect modification.

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Then in the next module,

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we'll extend that information into SPSS

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and the statistical techniques

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behind controlling for effect modification.

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And then in Module 11,

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we'll look at interpreting the results

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of effect modification in the public health literature.

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Effect modification and confounding are similar in concept

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but they're actually very different in practice.

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I recommend that you go back

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and review your EPI1 notes

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just to make sure you feel solid

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about the basic difference between the two.

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I've included the chapter

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from your EPI1 Gordis text on interaction for reading

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before you get into your current textbook

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because I think it will reinforce that solid grounding

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before you dive deeper into the detail and analysis piece.

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As always, please reach out with questions,

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and I'll see you in the next module.