tanggal : 03 September 2009
tempat : Lab Komputer Gd. Radio Putro, FK UGM
waktu : 13.15-15.00
Yak. Ketemu lagi di praktikum biostatistik selanjutnya! 😀 (ko seneng gitu si malah..heuheu).
Materi yg dibahas adalah bagaimana cara kita menghitung dan memperkirakan interval, dan menguji hipotesis.
Yuk mari kita lihat, apa aja yg bisa gw tulis dan post kali ini.. hehe ;p
Jawaban dari soal praktikum biostatistik 3 :
3.1 CONFIDENCE INTERVAL
1. In a sample of 100 healthy women between 25 and 29 years of age, systolic blood pressure was found to follow a normal distribution. If the sample mean blood pressure was 120 mm Hg and the population standard deviation was 10 mm Hg, what interval of blood pressure would represent an approximate 95% confidence interval for the true mean μ?
dgn menggunakan stata, untuk nyari confidence interval (ci), masukkan command –> cii (jml sampel) (mean) (std deviasi) = cii 100 120 10
klik enter, muncul lah hasil : [95% Conf. Interval] 118.0158 121.9842
sehingga, dari pilihan jawaban yg ada, jawaban yg tepat adalah : A. 118 to 122 mm Hg
2. How will the length of a confidence interval, for the population, mean change when :
a. sample size is increased? decrease
b. variation in the population is higher? increase
c. confidence level is increased from 95% to 99%? increase
d. sample mean is larger? stay the same
(diuji coba aja pake stata)
3. A 99% confidence interval implies?
jwbn : D. On average, we would expect 99 out of 100 of similarly constructed intervals to contain the true parameter.
4. Weight loss is a major manifestation of HIV infection. A study was carried out to analyze weight change in 9 male subjects with State IV HIV infection. The average weight loss per month for the 9 men was 5.97 kg/month with a sample standard deviation of 2.687 kg/month. Construct a 95% confidence interval for the true mean weight loss per month of HIV positive males in State IV HIV infection. Interpret the results.
Rumus dasar = mean -+ t (n-1 . 1 – alfa/2) s/akar ‘n’ .
Untuk nyari t(n-1.1-alfa/2) pake stata, masukkan : di invttail(b,1-0.05/2).
didapat hasil = 2.306 (pembulatan), setelah itu masukkan ke rumus dasar.
sehingga didapatlah hasil akhir 8.035 dan 3.9 😀
5. There is a general concern about the escalating costs of providing health care in Indonesia. One of the components contributing to the increasing costs is the length of the hospital stay of a patient. In a sample of 23 patients, the mean time was 4.5 days with a sample standard deviation of 1.3 days. Find a 95% confidence interval for the true mean length of hospital days.
Jwbn : masukin k command pd stata awal buat cari ci –> cii 23 4.5 1.3
hasilnya = [95% Conf. Interval] 3.937838 5.062162
3.2 HYPOTHESIS TESTS : I
1. The level of significance, alpha, is the probability of …
C. Rejecting a true null hypothesis
2. If an investigator rejects the null hypothesis …
B. s/he has committed a Type I error and C. s/he has committed no error
3. A Type II error is …
C. made if the null hypothesis is accepted when it is false
4. The p-value is …
C. the probability of the test statistic or any more extreme results, assuming the null hypothesis is true
5. A 95% confidence interval for the mean cholesterol level of adults over 65 years of age is (198, 208) mg/dl. The mean cholesterol level for adults 40-60 years of age is 190 mg/dl. If a two-sided hypothesis test of Ho: μ=190 mg/dl were performed, we would:
E. can’t tell
6. The 5% level of significance means:
B. we’re taking a 5% risk that our sample is unrepresentative if the null hypothesis is true
7. Iron-deficiency anemia is an important nutritional health problem in Indonesia. A dietary assessment was performed in 51 9 to 11 year-old males whose family were below the poverty line. The mean daily iron intake among these children was found to be 12.50 mg with a standard deviation of 4.75 mg. Suppose that the mean daily iron intake among a large population of 9-11 year-old boys from all income strata is 14.44 mg. We wish to test if the mean iron intake among the low-income boys is different from that of the boys in the general population. State the hypothesis that can be used to consider this question.
D. H0: μ = 14.44 versus H1: μ 6=14.44
3.3 HYPOTHESIS TESTS : II
1. A study was done to determine the effectiveness of an instruction booklet in improving nurses’ knowledge of testing for glycosuria in diabetes mellitus. A sample of 12 nurses was given a pretest prior to reading the booklet. After reading the booklet, the same nurses were given a posttest.
a) State the null hypothesis for determining if the instruction booklet was
effective. H0 : pretes sama dengan postes
b) State the appropriate alternative hypothesis. H1 : postes lebih baik dari pretes
c) The appropriate t-statistic is: paired t-test
d) The degrees of freedom associated with this test statistic are. 11(n-1)
2. One method for assessing the effectiveness of a drug is to note its concentration in blood and/or urine samples at certain periods of time after giving the drug. Suppose we wish to compare the concentrations of two types of aspirin in urine specimens at one time and measure the 1-hour urine concentration. One week later, after the first aspirin has presumable been cleared from the system, we give the same dosage of the other aspirin to the same person and note the 1-hour urine concentration. Since the order of giving the drugs may affect the results, we use a table of random numbers to decide which of the two types of aspirin to give first. We perform the experiment on 10 people. What statistical procedure would be appropriate for comparing the two types of aspirin?
paired t-test (krn masih menggunakan sampel yg sama)
3. A study was performed in 1086 to relate the use of oral contraceptives with the levels of various lipid fractions in a groups 163 non-pregnant, premenopausal women ages 21-39. The serum cholesterol among 66 current users of oral contraceptives was 201 + 37 (mg/dl) (Mean + Standard deviation), whereas for 97 nonusers it was 193 + 37 mg/dl. What statistical procedure would be appropriate for determining if cholesterol levels are affected by the oral contraceptive use?
2-sample t-test (krn independent)
4. In a pediatric clinic a study is carried out to see how effective aspirin is in reducing temperature. Twelve 5-year-old girls suffering from influenza had their temperatures taken immediately before and 1 hour after administration of aspirin. What is the appropriate statistical procedure for determining if aspirin is reducing the temperature? State the appropriate null and alternative hypothesis.
H0 : temperatur sebelum = sesudah. H1 : temperatur sebelum > sesudah
5. An investigator wishes to determine if sitting upright in a chair versus lying down on a bed will affect a person’s blood pressure. The investigator decides to use each of 10 patients as his or her own control and collects systolic blood pressure data in both the sitting and lying positions. What statistical procedure would be appropriate to determine the effect of position on blood pressure?
3.4 HYPOTHESIS TESTS : III
1. A clinical trial was designed to test a drug that was believed to decrease blood-clotting time. Forty subjects were selected and randomized to yield two groups, each with n=20. One group was given the drug and the other group was given a placebo, and served as a control. The mean clotting time, given in minutes, for the drug treatment group is 4.90 minutes with variance of 10.24 minutes squared. The mean clotting time for the control group is 7.45 and the variance is 12.96 minutes squared.
a) State the null hypothesis to test differences between the treatment and
control groups. H0 : hasil treatment dgn obat = placebo
b) State the appropriate alternative hypothesis. H1 : hasil treatment dgn obat tidak sama dengan placebo
c) Using the above results, set up the appropriate test. 2-sample t-test
klo mau diitung, mggunakan stata masukkan –> ttesti 20 4.9 3.2 20 7.45 3.6
2. A class experiment in pharmacology consisted of distributing packets of instant coffee to students. The contents of the packet were to be mixed with hot water and drank shortly before bedtime. The student received packets on two occasions: one time the packet contained a placebo and the other time it contained coffee with caffeine. Among other measurements, the students took their pulse rates (in beats per minute) before consuming the instant coffee or placebo and then again afterward. The students were classified as to whether they were coffee drinkers (those
who usually consumed two cups or more per day) or non-coffee drinkers (those who usually consumed one or fewer cups per day). The results for 65 non-coffee drinkers and 85 coffee drinkers are given below:
65 Non-Coffee Drinkers 85 Coffe Drinkers
Caffein Placebo Caffein Placebo
N 50 15 44 41
Mean 4.1 0.9 4.9 2
a) State the null and alternative hypothesis for determining if the response
is the same among Coffee Drinkers.
H0 : non-coffee drinkers, antara caffein = placebo.
H1 : non-coffee drinkers, antara caffein tidak sama dengan placebo.
b) What is the appropriate statistical procedure to test the null hypothesis
in (a)? 2-sample t-test
c) What are the degrees of freedom associated with the test statistic in
(b)? (44-1) + (40-1) = 83
d) State the null and alternative hypotheses to determine if the caffeine
response is the same between Non-Coffee and Coffee Drinkers.
H0 : kafein pada non-coffee drinkers = coffee drinkers
H1 : kafein pada non-coffee drinkers tidak sama dengan coffee drinkers
e) What is the appropriate statistic procedure to test the null hypothesis
in (d)? 2-sample t-test
f) What are the degrees of freedom associated with the test statistic in
(e)? pada yg cafein aja, sehingga –> (50-1) + (44-1) = 92
3. A recent study attempted to compare the working environment in offices where smoking was permitted with that in offices where smoking was not permitted. Measurements were made of carbon monoxide (CO) at 1:20 pm in 40 work areas. Where smoking was permitted, the mean CO=11.6 parts per million (ppm) and the standard deviation CO=7.3 ppm. Where smoking was banned, the mean CO=6.9 ppm and the standard deviation CO=2.7 ppm. What statistical procedure would be appropriate to see whether or not the mean CO is different in the two types of working environments?
2-sample t-test. di belakangnya dikasih unequal variable.
stata –> ttesti 20 11.6 7.3 20 6.9 2.7, unequal
gw ga ngerti apa yg gw ketik di atas. hiks hiks T.T