Stata versions 12 & 13 Week 4 - Practice Problems

Transcription

1 Stata versions 12 & 13 Week 4 - Practice Problems DUE: Monday February 24, 2014 Last submission date for credit: Monday March 3, Practice Screen Capture a Create a word document Name it using the convention lastname_lab1docx (eg bigelow_lab1docx) b Using your browser, go to the welcome page for PubHlth 640 c From there, navigate to the assignments page d Capture the picture of the ostrich e Paste the picture into lastname_lab1doc, inserting it into a table with 1 row and 1 column 2 Launch Stata and Start a Log of Your Session IMPORTANT Use extension log not scml a Launch Stata b Start a log of your session, with extension log Name it lastname_log1log (eg bigelow_log1log) c In the command window, type: set more off 3 Create a graph Save it Paste it into your word document a Launch Stata b In the command window, type: use clear c In the command window, type: histogram hyp, discrete d Save this as a png graph, with name hypertension_barpng, to your desktop e Paste your graph into lastname_lab1doc, again inserting it into a table with 1 row and 1 column hw_statlab1docx revised 3/2/2014 Page 1 of 5

2 4 Create a new data set in Stata using Data Editor a Execute the following commands to create a Stata data set with the following 4 observations: id type: numeric dob type: date gender type: string/character 1 3/26/1926 male /9/1956 female /1/1954 male /4/1951 female 1240 weight type: numeric * STEP 1: Clear the current data from memory clear * STEP 2: Define variables (lower case recommended) Set type Initialize to missing generate id= generate str8 dob_string="" generate str8 gender="" generate weight= * STEP 3: Click on DATA EDITOR icon to access an initially empty spreadsheet * Enter the data Then close the data editor window * STEP 4: Create a DATE variable called dob (date of birth) Drop string variable generate dob=date(dob_string, "MDY") format dob %tdnn/dd/ccyy drop dob_string * STEP 5: Create 0/1 indicator of female gender generate female=(gender=="female") * STEP 6: Label variables label variable id "Subject id" label variable weight "weight (lbs)" label variable dob "Date of birth" label variable female "0/1 female" * STEP 7: Create discrete variable value labels (the dictionary) label define femalef 0 "male" 1 "female" * STEP 8: Attach labels to discrete variable values label values female femalef list * Produce listing of data list * Save data set using FILE > SAVE AS hw_statlab1docx revised 3/2/2014 Page 2 of 5

3 4 Create a new data set in Stata using Data Editor - continued b Paste your listing of data into lastname_lab1doc, again inserting it into a table with 1 row and 1 column 5 Numerical Descriptives a Execute the following commands to produce the numerical descriptives indicated b Paste this portion of your stata log into lastname_lab1doc, again inserting it into a 1x1 table clear use " clear sort sex tabstat bweight, by(sex) col(stat) stat(n mean sd sem min q max) 6 One and Two Sample Inference a Execute the following commands to produce the standard one and two sample tests b Paste this portion of your stata log into lastname_lab1doc, again inserting it into a 1x1 table ** ONE CONTINUOUS VARIABLE 99% CI for mean using command ci ci gestwks, level(99) ** ONE CONTNUOUS VARIABLE - Test of null: mean=40 using command ttest ttest gestwks=40 ** ONE CONTINUOUS VARIABLE - Test of null: standard deviation = 1 using command sdtest sdtest gestwks=1 ** TWO CONTINUOUS VARIABLES - Test of null: Equality of 2 INDEPENDENT means using ttest sort sex ttest gestwks, by(sex) ttest gestwks, by(sex) unequal hw_statlab1docx revised 3/2/2014 Page 3 of 5

4 ** TWO CONTINUOUS VARIABLES - Test of equality of 2 independent variances using sdtest sdtest gestwks, by(sex) ** 1 DISCRETE (0/1) VARIABLE - Test of binomial proportion using bitest and prtest ** Test of null: proportion of female births = 50 generate female=(sex==2) bitest female=50 prtest female=50 ** 1 DISCRETE (0/1) VARIABLE - 95% CI for event probability using ci & option binomial ci female, binomial level(95) ** 2 DISCRETE (0/1) VARIABLES - Test of equality of probabilities using prtest sort sex prtest hyp, by(sex) **2 DISCRETE VARIABLES - chi square test using tab2 with option chi2 tab2 sex hyp, row column chi2 ** 2 DISCRETE VARIABLES - Fisher exact test using tab2 with option exact tab2 sex hyp, row column exact hw_statlab1docx revised 3/2/2014 Page 4 of 5

5 7 Simple and Multiple Linear Regression a Execute the following commands to produce some regressions b Paste this portion of your stata log into lastname_lab1doc, again inserting it into a 1x1 table clear * Depending on your Stata purchase, import EITHER hersdatadta or hersdata100dta * Choice 1 of 2: hersdatadta for Stata/IC use " clear * Choice 2 of 2: hersdatadta for SMALL Stata use " clear ** One predictor - continuous regress glucose BMI ** One predictor - nominal physical activity with design variables xi: regress glucose iphysact ** Multiple predictor model with both BMI and phsyact xi: regress glucose BMI iphysact ** Partial F test of BMI controlling for physact: 1 df Partial F testparm BMI hw_statlab1docx revised 3/2/2014 Page 5 of 5