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Understanding The Relationship Between Marijuana Initiation

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Understanding The Relationship Between Marijuana Initiation

Question

1) You are trying to understand the relationship between marijuana initiation and early onset psychosis. You gather a group of elementary school students and follow them for 20 years. Each year you meet with the students and assess whether they have initiated marijuana and if they have symptoms of early onset psychosis. The results of your study are noted below. At the end of your study, you realize that there was a mix up in your data and that 0.17 of people who had psychosis (both exposed and unexposed) were classified as not having psychosis and 0.17 of people who were not classified as having psychosis (both exposed and unexposed) actually had psychosis.
Marijuana initiation Psychosis
Yes No
Yes 1222 1287
No 703 1813

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– Which of the following study designs was likely used to gather this information?

Case control

Cohort study

Randomized control Trial

Cross sectional- What measure of association is most appropriate to calculate given the information provided?

Odds Ratio

Risk Ratio

Prevalence Ratio

Rate Ratio
– What type of misclassification has occurred?

Non-differential misclassification of disease

Differential misclassification of exposure

Differential misclassification of disease

Non-differential misclassification of exposure

– Used the information above, calculate the corrected values for the 2X2 table (round to the nearest number) along with the corrected measure of association (round to 2 decimal places)Understanding The Relationship Between Marijuana Initiation .

Marijuana initiation Psychosis
Yes No
Yes
No

Measure of Association =

– You stratify your data by gender because you think it might be an important covariable. Using the tables below calculate the stratified measure of association (round to 2 decimal places).

Table A: Females

Marijuana initiation Psychosis
Yes No
Yes 308 319
No 223 406

Measure of Association =

Table B: Males

Marijuana initiation Psychosis
Yes No
Yes 925 957
No 669 1218

Measure of Association =

– Is the crude association between marijuana initiation and early onset psychosis for the whole sample (the first table) descriptive of the associtation when you look at it broken down by gender (the last two tables)?

No

Yes

2) You are conducting a study looking at the relationship between the presence of a genetic marker and schizophrenia. Here is a 2×2 contingency table indicating if someone has a genetic marker and the presence (or absence) of schizophrenia. Below are the results of your study.

Genetic
Marker		 Schizophrenia
Yes No
Yes 30 23
No 39 62

– Calculate the odds ratio for Schizophrenia for those with the genetic marker compared to those without the genetic marker (round to 2 decimal places).
odds ratio=

– After you finish your study, you realize that some of your research assistants were using an old (and inaccurate) tool for assessment of the genetic marker. This means that among both groups (with and without schizophrenia), 15% of the people you listed as having the genetic marker actually didn’t and 15% of those you listed as not having the genetic marker actually did have the genetic marker.

differential misclassification of disease

non-differential misclassification of exposure

non-differential misclassification of disease

differential misclassification of exposure

– Using the previous misclassification, calculate the new odds ratio (round to 2 decimal places). When calculating the number of people in each cell of your new 2X2 round to the nearest whole number

Expert Answer

This solution was written by a subject matter expert. It’s designed to help students like you learn core concepts Understanding The Relationship Between Marijuana Initiation

Step-by-step

Step 1/2
1) Cohort studies are the type of research method utilised to collect this data. The risk ratio, sometimes referred to as relative risk, is the most suitable measure of association to determine given the facts presented. The type of misclassification that has occurred is non-differential misclassification of disease. Marijuana initiation Psychosis Yes No Yes 1224 1285 No 699 1817 Measure of Association = 1.31 Table A: Females Marijuana initiation Psychosis Yes No Yes 308 319 No 223 406 Measure of Association = 1.14 Table B: Males Marijuana initiation Psychosis Yes No Yes 925 957 No 669 1218 Measure of Association = 1.35
Explanation:
– The crude association between marijuana initiation and early onset psychosis for the whole sample by gender is not breakdowned. No
Step 2/2
2) odds ratio = 2.23 non-differential misclassification of disease new odds ratio = 2.34
To calculate the odds ratio for the original 2×2 table, we can use the formula: (ad) / (bc) = (3062) / (2339) = 2.23.
Explanation:
We may correct the data for the misclassification by doubling the percentage that were misclassified. For instance, we multiply by 0.85 (the percentage of individuals who were really correctly categorised) to reach 25.5 in order to rectify the 30 individuals with the genetic marker who were wrongly labelled as not having it. We can also change the other three table cells in a similar manner.
Genetic Marker Schizophrenia Yes No Yes 25 27 No 49 98 Using the formula again, we get (2598) / (2749) = 2.34 as the new odds ratio.
Final answer
1) Cohort studies are the type of research method utilised to collect this data. The risk ratio, sometimes referred to as relative risk, is the most suitable measure of association to determine given the facts presented. The type of misclassification that has occurred is non-differential misclassification of disease. Marijuana initiation Psychosis Yes No Yes 1224 1285 No 699 1817 Measure of Association = 1.31 Table A: Females Marijuana initiation Psychosis Yes No Yes 308 319 No 223 406 Measure of Association = 1.14 Table B: Males Marijuana initiation Psychosis Yes No Yes 925 957 No 669 1218 Measure of Association = 1.35
-No
2) odds ratio = 2.23 non-differential misclassification of disease new odds ratio = 2.34 To calculate the odds ratio for the original 2×2 table, we can use the formula: (ad) / (bc) = (3062) / (2339) = 2.23.

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We may correct the data for the misclassification by doubling the percentage that were misclassified. For instance, we multiply by 0.85 (the percentage of individuals who were really correctly categorised) to reach 25.5 in order to rectify the 30 individuals with the genetic marker who were wrongly labelled as not having it. We can also change the other three table cells in a similar manner.
Genetic Marker Schizophrenia Yes No Yes 25 27 No 49 98 Using the formula again, we get (2598) / (2749) = 2.34 as the new odds ratio Understanding The Relationship Between Marijuana Initiation

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