Cross-sectional studyCross-sectional study

Yuriko Suzuki, MD, MPH, PhDNational Institute of Mental Health, NCNP

yrsuzuki@ncnp.go.jp

Key issuesKey issues

• Why research?

• Descriptive study

• Hypothesis testing

• Association

• Sampling

• An example of cross-sectional study

Why research?Why research?

• To guide health practice and policy

• Because local research is often needed to guide local health practice and policy

• Because carrying out research strengthens research capacity

What is a hypothesisWhat is a hypothesis• A statement which describes what you expect to

find in a specific manner• Clearly stated• Testable and refutable• Not a mere research question or objective• Backed by sample size calculation, and an

appropriate design and analysis

ExampleExample

• Statement of the problem: mental health problems are said to be common in the aftermath of a disaster, and mental health problems are believed to be associated with physical damage

• Aim: to describe the association between physical damage and mental health problems

• Question: Are mental health problems associated with physical damage in time of disaster?

• Hypothesis: elderly people with poor mental health are more likely to have severe housing damage in time of disaster

Advantages of hypothesis-Advantages of hypothesis-driven researchdriven research

• Greater credence given to validity of findings

• Less risk of type I and II errorso Type I error: mistakenly see association while

there isn’t.o Type II error: mistakenly see no association

while there is.

• Ease of replication

What do epidemiologists What do epidemiologists do?do?

• Describeo Distribution of health-related states in a populationo Extent, type, severityo Who, where, when?

• Explaino Analytical epidemiologyo Hypothesis-driven etiological researcho Risk factors and causes

• Evaluateo Quasi-experimental studieso Randomized controlled trials

Association Association

Risk factor

Disease

Exposure Outcome

Independent

Dependent

ChanceBias

Confounding

True association?

Descriptive studiesDescriptive studies• Case series

• Cross-sectional studyo Multi-center (geographic variance)o Ecological correlation o Repeated surveys (temporal variance)

Who to study?Who to study?• Population

• Sampleo Advantage:

• time and costo Disadvantages:

• sampling error, • bias if sample is not representative of population

Random samplingRandom sampling

• Simple

• Systematic

• Stratified

• Multi-stage and cluster

How big a sample?How big a sample?

• Sample size calculation is important to avoid errors in interpreting findings:

• Type I errors: o The null hypothesis is rejected when it is in

fact, true (p value)• Type II errors:

o The null hypothesis is accepted when it is, in fact, false (power)

Prevalence study

• Suzuki Y, Tsutsumi A, Fukasawa M, et al. Prevalence of mental disorders and suicidal thoughts among community-dwelling elderly adults 3 years after the niigata-chuetsu earthquake. J Epidemiol. 21:144-50. 2011 13

Niigata

Earthquakes in NiigataEarthquakes in Niigata

• In 2004: The Niigata-Chuetsu earthquake

• 2004.10.23.5:56pm• Magnitude:6.8 in Richter scale• Seismic intensity:7 in Japanese scale• Damage:68 deaths 4805 injuries　　　　　

• In 2007: The Niigata Chuetsu-oki earthquake• 2007.7.16.10:13am• Magnitude:6.8 in Richter scale• Seismic intensity:6 in Japanese scale• Damage:15 deaths 2345 injuries　　　　　

Prevalence of mental health disorders among community dwelling elderly three year after the Niigata-Chuetsu earthquake

1. Face-to-face interviews were conducted to the older people above 65 in the severely damaged area by the Niigata-Chuestu earthquake

2. Diagnoses of mental disorder were confirmed using Mini International Neuropsychiatric Interview (M.I.N.I.), and quality of life (QOL) were measure by WHOQOL

3. The prevalence and its associated factors were described.

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4. Data collection Trained health professionals administered the

questionnaires and the following structures interviews;

5. MeasurementA) Diagnosis of mental disorders (M.I.N.I.)

a. Major depression (current, since the earthquake)b. Minor depression (current, since the earthquake) c. Suicidal tendency (current, since the earthquake)d. Posttraumatic stress disorder (current)e. Alcohol dependence and abuse (current)

B) QOL ： WHO/QOL-BREFa. Physicalb. Psychologicalc. Sociald. Environmental

MethodsMethods

Community-dwelling older adults (n=799)

Population of the older adults (65 and over) in the severely affected areas in Ojiya city (n=902)

ExclusionDead (n=42)Hospitalized (n=20)Institutionalized( n=15

)Moved out (n=24)

Completed interviews (n=496), Completion rate 62.1%

Unable to interviewAbsents (n=27)Due to disability (hearing, seeing, etc) (n=71)

Refusal to interview (n=215)

Results （１）： Flow of the study (2007.10.1-2008.1.11)

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ResultsResults （（ 22 ））Table 1. Characteristics of participants of the study of three year after the Niigata-Chuetsu earthquake in 2004 (n=473)　 　 n % Mean 95% CIGender 　

Male 190 40.2 Age

65-74 209 44.2 75+ 264 55.8 Average age 76.0 75.4-76.6

Marital statusMarried 328 69.3 Divorced 3 0.6 Bereaved 140 29.6 Never married 2 0.4

EducationElementary school 128 27.5 Koutouka 112 24.0 Chugakko 167 35.8 Koukou 20 4.3 Others

Numbers of year in education 8.2 8.1-8.4Number of cohabitant 3.9 3.7-4.1Previous psychiatric visit 19 4.3

Digit spam (3 digits)　 Incorrect 29 11.2 　　

Severity of disaster damageResultsResults （（ 33 ）） I. Prevalence

study

Prevalence of mental disorders in 2 weeks and past 3 years Prevalence of mental disorders in 2 weeks and past 3 years

among the older people living in community by gender (n=444)among the older people living in community by gender (n=444)

Results （ 4 ）

**

**

**:p<0.05

2w 3yMajor depression

2w 　 3yMajor and Minor depression

Current PTSDEarthquake Other events

Current alcohol-dependence, abuse

2w 3ySuicidal tendency

Pre

vale

nce

rate

(%

)

**

**

(n=446) (n=443) (n=245) (n=445) (n=88) (n=51)

Results （ 5 ）

The percentage of those who met criterion A and B of PTSD in DSM-IV-TR by exposure of the earthquake and the other events

Results （ 7 ）

QOL mean : male 3.54 (95%CI:3.47-3.60) female 3.48 (95%CI:3.43-3.53)

Results （ 8 ） Results of regression analysis for quality of life and interviewees’ basic characteristics (n=439)Variables Physical 　 Psychologic

al　 Social 　Environmental Mean QOL score

　 Coef. Coef. 　 Coef. 　 Coef. Coef.Gender -0.05 -0.07 0.07 -0.10 * -0.05 (male=0, female=1)

Age -0.01 0.00 0.00 0.00 0.00 year

Marital status 0.03 0.01 -0.08 -0.04 0.00 (not married=0, married=1)

Number of cohabitants 0.02 0.03 * 0.02 0.03 ** 0.03 *

Years in education -0.03 0.00 0.00 -0.01 -0.01

Previous psychiatric visit -0.13 -0.03 -0.06 0.04 -0.03

(never=0, yes=1)

Severity of disaster damage in 2004

-0.05 * -0.03 -0.04 -0.03 -0.04 *

Physical illness -0.29 ** -0.17 ** -0.01 0.00 -0.15 **

Intercept 4.9 3.6 4.1 3.6 3.9 Adjusted R2 0.060 　　 0.022 　 　 0.003 　　 0.015 　 0.034 　*:p<0.05, **:p<0.01

• Prevalence of major depression and PTSD was lower than previous researches in disaster settings in other countries （ 6.4-11%, 4.4-25% respectively in literature ） .

• The prevalence of major depression since the earthquake was 4.4%, within the range of the prevalence in non-disaster community studies (0.9-9.4% in literature).

• Among males, the alcohol related problems were reported in 6.0% and among females, major or minor depression were reported in 10.0%, and suicidal tendency were seen in 8.0% of the interviewees.

• Pathological level→ about same level as usual• Subclinical level → require further attention to promote

their mental health

Discussion （ 1 ）

• In general, having fewer cohabitants, and greater degree of disaster damage, and any physical illness were attributing to the worse quality of life.

• The risk factors for poor QOL were severity of disaster damage, and physical illness in physical domain, fewer cohabitants and physical illness in psychological domain, being female, and fewer cohabitants in environmental domain.

• Mental health and physical health care would be better if provided hand in hand, and social support persistently had favorable effects on QOL among disaster affected elderly people.

Discussion （ 2 ）