Examining the Relationship Between Two Variables

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Examining the Relationship Between Two Variables. (Bivariate Analyses). What type of analysis?. We have two variables X and Y and we are interested in describing how a response (Y) is related to an explanatory variable (X).

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Examining the Relationship Between Two Variables

(Bivariate Analyses)

What type of analysis?
• We have two variables X and Y and we are interested in describing how a response (Y) is related to an explanatory variable (X).
• What graphical displays do we use to show the relationship between X and Y ?
• What statistical analyses do we use to summarize, describe, and make inferences about the relationship?
Fit Y by X in JMP

Y nominal/ordinal Y continuous

X continuous X nominal/ordinal

List of Variables

id – ID # for infant & mother

leng – length of infant (in.)

weight – birthweight (lbs.)

gest – gestational age (weeks)

mage – mother’s age

mnocig – mother’s cigarettes/day

mheight – mother’s height (in.)

mppwt – mother’s pre-pregnancy

weight (lbs.)

fage – father’s age

fedyrs – father’s education (yrs.)

fnocig – father’s cigarettes/day

fheight – father’s height

lowbwt – low birthweight indicator

(1 = yes, 0 = no)

mage35 – mother’s age over 35 ?

(1 = yes, 0 = no)

smoker – mother smoked during preg.

(1 = yes, 0 = no)

Smoker – mother’s smoking status

(Smoker or Non-smoker)

Low Birth Weight – infant birthweight

(Low, Normal)

Example: Low Birthweight Study

Y = birthweight (lbs.) Continuous

X = gestational age (weeks)Continuous

Example: Low Birthweight Study(Birthweight vs. Mother’s Smoking Status)

Y = birthweight (lbs.) Continuous

X = mother’s smoking status (Smoker vs. Non-smoker)

Nominal

Example: Low Birthweight Study(Birthweight Status vs. Mother’s Cigs/Day)

Y = birthweight status(Low, Normal)Nominal

X = mother’s cigs./day Continuous

P(Low|Cigs/Day)

Example: Low Birthweight Study(Birthweight Status vs. Mother’s Smoking Status)

Y = birthweight status(Low, Normal)Nominal

X = mother’s smoking status (Smoker, Non-smoker)Nominal