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Cross-sectional study. Yuriko Suzuki, MD, MPH, PhD National Institute of Mental Health, NCNP Key issues. Why research? Descriptive study Hypothesis testing Association Sampling An example of cross-sectional study. Why research?. To guide health practice and policy

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cross sectional study

Cross-sectional study

Yuriko Suzuki, MD, MPH, PhD

National Institute of Mental Health, NCNP

key issues
Key issues
  • Why research?
  • Descriptive study
  • Hypothesistesting
  • 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 hypothesis
What 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
  • 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 driven research
Advantages of hypothesis-driven research
  • Greater credence given to validity of findings
  • Less risk of type I and II errors
    • Type I error: mistakenly see association while there isn’t.
    • Type II error: mistakenly see no association while there is.
  • Ease of replication
what do epidemiologists do
What do epidemiologists do?
  • Describe
    • Distribution of health-related states in a population
    • Extent, type, severity
    • Who, where, when?
  • Explain
    • Analytical epidemiology
    • Hypothesis-driven etiological research
    • Risk factors and causes
  • Evaluate
    • Quasi-experimental studies
    • Randomized controlled trials

Risk factor


True association?








descriptive studies
Descriptive studies
  • Case series
  • Cross-sectional study
    • Multi-center (geographic variance)
    • Ecological correlation
    • Repeated surveys (temporal variance)
who to study
Who to study?
  • Population
  • Sample
    • Advantage:
      • time and cost
    • Disadvantages:
      • sampling error,
      • bias if sample is not representative of population
random sampling
Random 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:
    • The null hypothesis is rejected when it is in fact, true (p value)
  • Type II errors:
    • The null hypothesis is accepted when it is, in fact, false (power)
prevalence study
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

earthquakes in niigata
Earthquakes 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 deaths4805injuries
  • 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 deaths2345injuries

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

  • Face-to-face interviews were conducted to the older people above 65 in the severely damaged area by the Niigata-Chuestu earthquake
  • Diagnoses of mental disorder were confirmed using Mini International Neuropsychiatric Interview (M.I.N.I.), and quality of life (QOL) were measure by WHOQOL
  • The prevalence and its associated factors were described.
  • Data collection

Trained health professionals administered the questionnaires and the following structures interviews;

  • Measurement
    • Diagnosis of mental disorders (M.I.N.I.)
      • Major depression (current, since the earthquake)
      • Minor depression(current, since the earthquake)
      • Suicidal tendency(current, since the earthquake)
      • Posttraumatic stress disorder (current)
      • Alcohol dependence and abuse (current)
      • Physical
      • Psychological
      • Social
      • Environmental

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

  • Exclusion
    • Dead(n=42)
    • Hospitalized (n=20)
    • Institutionalized( n=15)
    • Movedout(n=24)
  • Community-dwelling older adults (n=799)

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

  • Completed interviews (n=496), Completion rate62.1%
  • Unable to interview
    • Absents(n=27)
    • Due to disability (hearing, seeing, etc) (n=71)
  • Refusal to interview (n=215)
results 3

I. Prevalence study

Severity of disaster damage

Prevalence of mental disorders in 2 weeks and past 3 years among the older people living in community by gender (n=444)


Prevalence rate (%)







Major and Minor depression


Suicidal tendency


Major depression

Current PTSDEarthquake

Other events

Current alcohol-

dependence, abuse



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

(n=446) (n=443) (n=245)

(n=445) (n=88) (n=51)




: male 3.54 (95%CI:3.47-3.60)

female 3.48 (95%CI:3.43-3.53)



  • 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


  • 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.