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Mental health of middle aged men and women - Depressive symptoms

DATA ANALYSIS EXERCISE

Investigators have been interested in the mental health of middle aged men and women. Among other aims, they wanted to study the association between material circumstances and depressive symptoms.

They decided to use the CES-D questionnaire to measure depressive symptoms. The CES-D score of depressive symptoms is constructed from 20 questions.

The answers for each question are on scale 0-3, and the overall score is on scale 0-60. Score 0 means no depressive symptoms, score 60 means the highest score of depressive symptoms. Researchers studied existing literature to find baseline information for calculation of required sample size for their survey.

They found that they might expect mean score of CES-D=12 among 75% of the population with better material circumstances and CES-D=15 among 25% of population with worse material circumstances, assuming standard deviation=10 in both groups of population.

Q1: based on these data please calculate the sample size required for a study with alpha error=0.05, and required power=0.90.

Investigators then collected data from 960 men and women in a longitudinal study of mental health.

Q2: Is sample size appropriate given your sample size calculation in step 1? Please explain.

The data available for this exercise are drawn from the baseline survey conducted in 1999 and from second data collection in 2002. In 2002, all participants were asked series of 20 question about depressive symptoms and CES-D score of depressive symptoms was constructed (variable depress; details above). All other variables (including material deprivation used as an indicator of material position) were collected in 1999 during interviews in participantsí homes. The sample of 960 individuals used in this exercise are men and women who were depression free at the baseline survey (baseline score of depression is not included in this dataset).

The dataset assessment.dta

Based on evidence from previous studies in various populations it has been decided that a CES-D score of 16 and more indicates depression. Score of less than 16 indicates no depression.

The aim and hypothesis: The investigators aimed to study the relationship between material circumstances of the individuals at baseline and depression 3 years later. It has been hypothesized that people in worse material position (those classified as materially deprived in our data) have higher risk of depression than people in better material position.

Q 3. Summarise the study sample

Before looking at relationships between the score of depressive symptoms and material deprivation it is important to know the characteristics of the study sample. Describe the sample in terms of available variables. Use no more than two tables for this part.

Q 4. Evaluate the association between dichotomised score of depressive symptoms and possible risk factors other than material position. Next, evaluate the association between dichotomised score of depressive symptoms and indicator of material position. Use classical analysis to identify possible confounders and effect modifiers (if any). Moreover, would you confirm the original hypothesis saying that people living in worse material circumstances have higher risk of depression than those living in better material circumstances?

Q 5. Look at the association of material position and other risk factors with score of depressive symptoms using original score (on a continuous scale) using linear regression. Give an interpretation of these results.

Q 6. Please discuss whether results from two types of analysis (using dichotomised outcome and using continuous outcome) agree or disagree. Make brief conclusions in response to the aim and hypothesis of the study.

Mental health of middle aged men and women - Depressive symptoms

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