Steps to Creating A Research Question (Hypothesis):

1) Brainstorm possible risk factors & protective factors2) Choose one (or a few) ‘factors’ to analyze3) Predict the type of relationship between factors & outcome4) Write your research question

Quantify your prediction in step 3 by…

Calculating the association between risk/protective factors & outcomes

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Step 3: Predict the type of relationship between factor and outcome

Does _____________ cause _____________?(Risk Factor) (Outcome)

1 min

Today’s example:Does not getting a vaccine cause influenza?

Remember why we try to avoid this word?

• To figure this out we can compare incidence rates for people who:– Have or Do not have the Risk Factor– Have or Do not have the Outcome

• For example: – Is not getting vaccinated associated with

getting the flu?• We’ll us a 2x2 Contingency Table to sort all

this out!

Is _____________ associated with _____________?(Risk Factor) (Outcome)

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• Who had the FLU in the past year?– FLU: Go to the back of the room– NO FLU: Go to the front of the room

• Who got a FLU SHOT in the past year?– FLU SHOT: Go to the door side corner– NO FLU SHOT: Go to the window side corner

Is _____________ associated with _____________?(Risk Factor) (Outcome)

What goes into the 2x2 table?We just collect data on people based on RF & outcome.

2 x 2 Contingency TableAfter the population is sampled (like we just did), we add the values into the table:

– Flu shot/Flu (a)– Flu shot/No Flu (b)– No Flu shot/Flu (c) – No Flu shot/No Flu (d)

Outcome Variable

Risk

Fac

tor

Varia

ble

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2 x 2 Contingency Table

Let’s crunch some numbers!

Outcome Variable

Risk

Fac

tor

Varia

ble

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Our big goal? Find RELATIVE RISK!

Relative Risk (RR): A ratio of the probability of the outcome occurring in the exposed (risk factor) group versus a non-exposed (no risk factor) group.

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RF

No RF

Review: What is Incidence?

• What does it mean?– New cases of OUTCOME (flu) in population over time– Doesn’t tell us anything about RF (flu shot) on it’s

own– So we must compare 2 groups’ Incidence rates to

learn how the flu shot might be linked to flu• What is the formula?– Look back at your notes!

TIME cancels when we divide a fraction by a fraction because it is the same for the RF & NO RF group!

Calculating Relative RiskIf the incidence of the flu in the not vaccinated subpopulation is different

from the incidence of the flu in the vaccinated subpopulation, then vaccination and getting the flu are observed to be ASSOCIATED.

Outcome Variable

Risk

Fac

tor

Varia

ble

1m

Calculating Relative RiskStep 1: Focus on the risk factor row. Remember, not vaccinated is our risk factor.Step 2: Calculate the incidence rate of the flu for those who are not vaccinated

incidence rate =

Outcome Variable

Risk

Fac

tor

Varia

ble

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Calculating Relative RiskStep 3: Focus on: no risk factor row. Remember, vaccinated is our no risk factor group.Step 4: Calculate the incidence rate of the flu for those who are vaccinated

incidence rate =

Outcome Variable

Risk

Fac

tor

Varia

ble

2m

Put it all together to find RELATIVE RISK!

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What does my RR value mean?RR = 7.0? There is a VERY strong association (7x)• The RF group is 7 times as likely to experience the outcome.

RR = 1? There is no association. • The incidence in the RF group and no RF group were the same. RR = 1.5? There is a strong association (1.5x)• The risk factor group is 1.5 times as likely to experience the outcome. (50% more

likely)

RR = 1.1? There is some association (1.1x)• The risk factor group is 1.1 times as likely to experience the outcome. (10% more

likely)

RR = 0.9? There is a inverse association• Exposure to risk factor decreases the risk of the outcome by 10%

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Focus on the decimal when RR is 1.0 – 1.99

RR = 1.04.04 = 4%

The RF group has 4% greater chance of experiencing outcome

Setting Up Your 2x2 TableOur goal: Get RR ≥ 1. So we need the TOP to be larger than the bottom. The top should represent:

NEGATIVE RISK FACTOR & BAD OUTCOME

BAD

NEGATIVE

Group Practice

10-15 m

NEGATIVE

BAD

• What are we trying to prove by calculating the association (by getting a RR value)?– That the RF & outcome are RELATED or LINKED,

not that there is a DIRECT CAUSE relationship• What other factor might people who get the

flu shot and don’t get the flu have in common?– Health-conscious?– Hand-washers?– Less exposed to contagious environments?– More access to health care?

Is _____________ associated with _____________?(Risk Factor) (Outcome)

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