While, the study hypothesis clearly stated in the abstract which is "no association with use of cigars, pipe, tobacco, alcoholic beverages, or tea, and a strong association between coffee consumption and pancreatic cancer was evident in both sexes, and week positive association between pancreatic cancer and cigarette smoking.
The way of control group selection – lead to Selection Bias , because when they select 273 pts with cancer other them pancreatic cancer such as stomach Ca. , of course these pts were stopped to consume coffee and cigarette smoking.
There is no any information about exclusion people.
According of design of the study, Cases and control groups selected according to specific criteria for these cases and controls, method of data collection were interview and stratification according to age and sex which have a bias in selection and information.
The analysis of data were with using measures of association, Bradford hill "criteria for causality" and statistically significant level and finally the author explained about this estimate which emphasizes the need to determine whether the association exists in other data and to evaluate it's causal or non causal nature.
Were patients with a histologically confirmed diagnosis of pancreatic cancer in 11 Boston & Rhode Island Hospitals from 1974 to 1979.
Were selected from all patients who were hospitalized at the same time as cases, and they were selected from other inpatients hospitalized by attending physicians who had hospitalized the cases and controls series composed of two principle diagnostic groups.
In the study the coffee consumption and cigarette smoking are closely related to each other because (it is rare to find smoker who doesn’t drink coffee). And the data showed a consistent association of pancreatic Ca with coffee drinking with each category of smoking so that the main exposure in addition to coffee consumption is cigarette smoking.
Q3. A. what was the main exposure under investigation?
Q.3.B. how was it defined and measured in this study?
It defined as "there is a strong association between coffee consumption and pancreatic cancer was evident in both sexes.
It measured by asking the participant about the number of cups consumed per day, two cups, three or more cups.
Q.3 .C. Method of measurement – precision? Validity?
This measurement was not précised or valid, because the interviewer could ask another question such as duration of coffee consumption rather than the numbers of cups as we know this was lead to information Bias.
Q4. A. what was the main out come under investigation? P-value Adjusted interval Confidence interval R.R Variable (P~0.001) After adjustment for cigarette smoking Men 1.4 Women 1.5 1.1 to 1.9 1.4 % Tobacco Men 1.3 Women 0.8 0.6- 1.3 0.9 Alcohol Men 0.7 Women o.7 Men 0.5 -1.1 Women 0.5-1.2 - Tea P 0.001 Men 2.6 Women 2.3 Men 2.6 Women 1.2-4.6 2 cups 1.7 3 or more 2.7 coffee
These confounders measured with using the method of mantel and Hansel and its extension (test of significance, estimates of adjusted relative risk) and their confidence limits except age, sex, life style.
Q 6. A. data presentation and analysis- how clear and complete?
Descriptive characteristics of study population
Cases : were patients with histologic diagnosis of cancer of the exocrine pancreases.
Not included (exclusion ):
Pts. With tumor of islet cells.
Periampullary duodenal mucosa or ampula of vater.
Non white patient.
Residents of countries other than the United States.
Pts. Older than 79y.
Pts. whose interview information was judged by the interviewer to be of questionable reliability.
Controls : where the patient who were under the care of the same physician in the same hospital at the same time of an interview with pt. with pancreatic cancer, With two principal diagnostic group, pt with cancer other than cancer of the pancreas and biliary tract, respiratory tract, bladder. The control pt with cancer the tumer was in breast, colon, rectum, stomach, small intestine, ovary, prostate, cervix, and melanoma.
Other gastroenterologic conditions : benign tumors, varicose veins or phlebitis, genitourinary disorders, neurologic disorders, gynecologic disorders, and other conditions.
Q 6.B. complete presentation of numbers: No. Excluded from study No. Cases 8 Non-white 578 identified 4 Residents of other countries 405 interviewed 8 Pt. older than 79y 20 died 16 Whose interview information was questionable reliability 33 Discharged before interview 78 Too sick 369 pts. Analysis based on data from the remaining 14 Language difficulties 26 Refused to interview
Two principal diagnostic groups No. 371-pt. with other disorder No. 273-pt.with other pancreas&biliary tract No. Controls: 70 Hernia 65 Breast tumor 1118 Eligible pt. 41 Colitis enteritis or diverticulities 60 Colon 700 interviewed 26 Bowel obstruction,adhesion,fistula 25 Rectum 9 Died 17 gastritis 24 Stomach 131 Discharged before interview 47 Other gastroenterologic 9 Small intestine 179 Too ill 29 Benign tumor 8 Ovary 26 Language problems 21 Varicose vein,phlebities 8 Prostate 73 refused 20 Genitourinary disorder 7 Cervix 20 Neurological disorder 16 Melanoma 16 Gyrecologic disorders 15 Lymphoma 64 Other conditions
Cont.. Q6 B The analysis consisted of 644 pt. The analysis consisted of 644 pt. The analysis consisted of 644 pts No. Exclusions 17 Non-white 5 Foreign resident 4 Older than 79y 30 Whose interview un reliable
Data presentation and analysis with using measures of association and risk (R.R, adjusted relative risk, confidence interval and statistically significance, mantel test, chi-square) all of these measure were clear and complete.
Control for cofounders not complete because the researcher control the confounder by using stratification and statistical modeling in the analysis while in the design no any of randomization, restriction, and matching used.
Chance: when a multiple characteristics of two groups are test for "statistically significant" differences, one or more of those characteristics may seem "significant by chance".
selection , appear during control selection because the pt. with control group with cancer has a stomach cancer these pt. may decrease or stopped taking coffee and cigarette smoking due to their illness.
How do the findings relate to the aims / study hypothesis?
About the alcohol : "it seems unlikely that alcohol consumption has any role in the origin of cancer of pancreas because this substance cause in chronic pancreatitis this approved in study hypothesis when the author said that no association between alcohol and pancreatic cancer.
2. There is a small excess of men with the disease in proportion to women would seem to be more suggestion of a role of coffee rather than for cigarettes. This appears and explained that there is a weak positive association between cigarette smoking and pancreatic cancer.
3. The author estimate the proportion of pancreatic cancer that is potentially attributable to coffee consumption to be slightly more their 50%, this percentage explained as reported in study hypothesis there is a positive association between pancreatic cancer & coffee consumption but need more emphasizes to evaluate its causal and uncausal nature.
Q8. B. How genaralizable do you thinks the variables are?
In this study the variables couldn’t generalized due to presence of several types of bias and this study need more emphasizes the need to determine whether the association exists in other data and to evaluate its causal or non causal nature, so that variables couldn’t generalized.
Q8. C. is the interpretation of results, and hence, the conclusions justified?
Yes, it's for example when the interpretation of coffee consumption in table No. -4-
Women men 2.3 2.6 Adjusted relative risk 1.2-4.6 1.2-5.4 Confidence interval