Using SPSS for Chi Square UDP 520 Lab 5 Lin November 8 th, 2007

Outline Dataset Review t-test Chi-square Exercise

BMI Body mass index (BMI) is a measure of body fat based on height and weight that applies to both adult men and women. –Under & normal weight: BMI <25 –Overweight & obesity: BMI ≥ 25

Dataset – WLTP 1000 adults aged 18+ (males and females) were recruited to study the effectiveness of Weight Loss Training Program (WLTP) Variables –Sex (female=1) –BMI_1(before WLTP) –BMI_2(after WLTP) –Urban or suburban (urban=1) –Overweight_1 (overweight before WLTP) (overweight=1) –Overweight_2 (overweight after WLTP) (overweight=1)

Question 1 Is BMI significantly different between people who live in an urban area and those who live in a suburb area before WLTP? Independent samples t-test

Question 1 – Step by Step Step 1: Making assumptions and meeting test requirements –Sampling is random –Level of measurement is interval-ratio –Sampling distribution is normal Step 2: Stating the null hypothesis Step 3: Selecting the sampling distribution and establishing the critical region –Sampling distribution = Z distribution –Alpha = 0.05, two-tailed –Z(critical) = ±1.96

Question 1 (cont.) Step 4: Computing the test statistic in SPSS

Question 1 (cont.) Step 5: Making a decision and interpreting the results of the test Result (Z obtained) Indicate whether result is significant or not (based on your predetermined alpha)

Question 2 Is there any relationship between living in a suburban area and being overweight before WLTP? –Under & normal weight: BMI <25 –Overweight & obese: BMI ≥ 25 Chi Square test

Question 2 – Step by Step Step 1: Making assumptions and meeting test requirements –Random sampling –Level of measurement is nominal Step 2: S tating the null hypothesis –H 0 : Living in an urban area and being overweight are independent –H a : Living in an urban area and being overweight are dependent Step 3: S electing the sampling distribution and establishing the critical region –Sampling distribution = χ 2 distribution –Alpha = 0.05 –Df = (r-1)(c-1) = 1 (a 2-by-2 table) –χ 2 (critical) = 3.481

Question 2 (cont.) Step 4: computing the test statistic in SPSS

Question 2 (cont.) Step 5: making a decision and interpreting the results of the test Result ( χ 2 obtained)

Question 2 (cont.) The nominal symmetric measures indicate both the strength and significance of the relationship between the row and column variables of a crosstabulation.

Exercise Does a significant relationship exist between living in a suburban area and being overweight after WLTP? Does a significant relationship exist between being a male and overweight before WLTP? Does a significant relationship exist between being a male and overweight after WLTP?