Cross-sectional study

Question 1

Epidemiologic study

Answer 1

Question 2

Types of cross-sectional study

Answer 2

1. )Descriptive cross-sectional study
2. )Analytic cross-sectional study

Question 3

Descriptive cross-sectional study

Answer 3

Prevalence

Question 4

Analytic cross-sectional study

Answer 4

Associated factors

Question 5

Descriptive cross-sectional study

Answer 5

Determine the magnitude & distribution of disease within a population by person, place, & time:

A.)What

B.)Who

C.)Where

D.)When

Disease frequency

Question 6

Descriptive cross-sectional study

Answer 6

Single examination OR cross section of the population at 1 point in time

Snap shot

Prevalence survey

Designed to determine “What is happening right now?”

Question 7

Descriptive cross-sectional study

Answer 7

Example: To determine the prevalence of manourished children in population

(General idea of descriptive cross-sectional studies)

Question 8

Descriptive cross-sectional study

Answer 8

Assess BOTH the EXPOSURE & OUTCOME SIMULTANEOUSLY, at a SINGLE POINT OF TIME

Sometimes, MULTIPLE ASSOCIATED FACTORS/EXPOSURES & OUTCOMES can also be collected at a SINGLE POINT OF TIME

• Malnourished children are measured according to their weight, height, head circumference & BMI
• Diseases are checked with previous & current medical report
• Maternal factors are measured according to the maternal education level

Question 9

Descriptive cross-sectional study

Answer 9

• Sample from the population selected is analysed as a whole

Question 10

Descriptive cross-sectional study

Answer 10

A population is defined as the presence OR absence of exposure and the presence OR absence of disease for each individual is determined at the same time; but not compared as they are all considered as the same whole group

• Population indicates children, adults or both but in this case it is children & mother

Calculates prevalence

Question 11

There are 2 types of Prevalence study

Answer 11

1. )Point Prevalence
2. )Period Prevalence

Question 12

1.)Point Prevalence

Answer 12

Prevalence rate at 1 point in time

Number of all current cases (old+new) of a disease at 1 point in time in a defined population

Formula:

Point Prevalence = Number of all current cases (old+new) of a disease at a given point in time / Estimated population at the same point in time * 100

(Which means that at that time of data collection, they have that specific condition)

Question 13

2.) Period Prevalence

Answer 13

Prevalence rate at over a period of time

Frequency of all current cases (old+new) existing during defined period of time in a defined population

Formula = Number of existing cases (old+new) of a disease during a given period of time / Total population at start of the study * 100

(Eg: Did you have any mammogram over the past 2 years?)

Question 14

This figure shows occurrence of TB in a population of 100 over 4 years. During these years, no death or migration has occurred.

What is the prevalence of TB in Jan 2000? [Point Prevalence]

Answer 14

5 [Only in January] / 100 [Total population]

(Each horizontal line represents 1 patient)

Question 15

This figure shows occurrence of TB in a population of 100 over 4 years. During these years, no death or migration has occurred.

What is the incidence of TB from Jan 2000 - Jan 2003?

(Incidence means remove all the old cases, involve only the new cases)

Answer 15

15 [New cases only] / 95 [Cut out 5 from 100, which is the old cases from the total population as the current population has to be free of the disease]

Question 16

This figure shows occurrence of TB in a population of 100 over 4 years. During these years, no death or migration has occurred.

What is the period prevalence of TB from Jan 2000 - Jan 2003?

(Prevalence means include all the old+new cases)

Answer 16

20 [Include old+new cases] / 100 [Total population]

Question 17

In conclusion, do take note that

Answer 17

1. ) Prevalence = Old + new cases / Total population
2. ) Incidence = New cases / Total population [Free from outcome and / or disease]

Question 18

An example of point & period prevalence in interview studies of Asthma

Answer 18

Question 19

Analytic cross-sectional study

Answer 19

Analytic cross-sectional study is defined as a study that examines the relationship between diseases ( or other health related characteristics ) and other variables of interest as they exist in a defined population at 1 particular time

( Eg: Why are these variable related & how does it affect others? )

Question 20

Analytic cross-sectional study

Answer 20

Simplest form in observational analytic studies

Prevalence study

Single examination OR cross section of the population at one point in time

Snap shot

A population is defined as the presence OR absence of exposure & the presence & absence of diseases for each individual is determined at the same time and compared

Useful for chronic diseases rather than short-lived diseases

Note: Most cross-sectional studies are prevalence studies

Question 21

Example: To determine the relationship between Osteoarthritis (OA) & Obesity in Region A

Answer 21

2 * 2 Table is suitable for the most & all types of studies (1 factor in 1 table )

• Obesity is the factor
• Osteoarthritis (OA) is the outcome / disease

Question 22

Data analysis for analytical cross-sectional study

Answer 22

ODD’S RATIO

Question 23

Further details on Analytical & Experimental Studies

Answer 23

1.) Analytical studies includes 3 types of studies:

A.) Cross-sectional studies

B.) Case-control studies

C.) Cohort studies

• As for cross-sectional studies, prevalence data is collected
• As for case-control studies, no data is collected
• As for cohort studies, incidence data is collected
  2. ) As for experimental studies, incidence data is collected

Note: In case-control studies, for instance, smoking which is associated with lung cancer. If the total population is 200, and 100 of them has lung cancer while another 100 is set as control, we cannot conclude that 50% of the whole population is having lung cancer. Thus, case-control studies does not provide any information regarding the population accurately

Question 24

Further details on Analytical & Experimental Studies

Answer 24

1.) Analytical studies includes 3 types of studies:

A.) Cross-sectional studies

B.) Case-control studies

C.) Cohort studies

• As for cross-sectional studies, at one time point OR period, retrospective study are involved
• As for case-control studies, retrospective study are involved
• As for cohort studies, usually prospective study are involved
  2. ) As for experimental studies, prospective studies are involved

Note: In retrospective studies, ask for further previous history

Question 25

Designing a cross-sectional study (survey)

Answer 25

1. ) What is your research question?
2. ) Is the design appropriate for yout study? - Type of study design
3. ) Who are you going to study? - Select population size & categories
4. ) How are you going to obtain your sample? - Different types of sampling methods
5. ) Is there risk of ‘Selection Bias’? - Usuallu use ‘Randomization’ method, not according to convenience
6. )How will you collect your data? - ‘Self-administered’ questionnaire & Google forms (more accurate)
7. )Plan for data analysis - Include prevalence, incidence & associated factors

Question 26

Advantages of cross-sectional study

Answer 26

1. ) Short duration & quick results
2. ) Relatively inexpensive (no intervention & follow-ups needed)
3. ) Useful initial overview of the problem
4. ) Starting point in prospective cohort studies for screening out already existing conditions ( Which means cross-sectional studies are conducted first, then comes the cohort studies to rule out the population with existing conditions from the whole total population, before proceeding to the cohort studies further )
5. ) Can study association of several risk factors with the disease in question

( Eg: Multiple risk factors related to malnutrition )

6.) Stronger likelihood of participation as the respondents participate one time

Note No.4: Question is discussing about risk factors of smoking which leads to IHD [Incidence]

Smoking ——> IHD [Incidence]

• Analytical cohort studies mainly involves incidence cases only:
  a. ) First, perform analytical cross-sectional studies to rule out and remove the existing IHD patients
  b. ) 1000-10=990 [Free from IHD]
  c. ) Find out among them, who are smokers & non-smokers

Question 27

Disadvantages of cross-sectional study

Answer 27

1.) Since exposure & disease are measured at the same point in time, not possible to establish temporal relationship between exposure & the onset of the disease; It requires 2 criterias: exposure & outcome

A.)Eg: Exposure to smoking and burning leads to outcome like lung cancer

B.)Eg: Exposure of smoking for 20 years & burning for 3 months which leads to outcome like respiratory symptom

2. )Cannot reflect causal relationship [Strong relationship-direct cause]
3. )No incidence rate [Only prevalence is obtained]
4. )Increased bias potential (regarding selection of population)
5. )Not suitable for diseases of short duration
6. )Cases of diseases of long duration are over-represented (Prevalence = Incidence * Duration)
7. )Inefficient for rare disease - Needs a large sample size

[Eg: If there are 500 sample size, only 1 sample has the rare disease, while the other 499 does not contain the disease, the study will be unfair & inefficient]

[Note: As for rare diseases, case control studies are more efficient & suitable]

Question 28

Recap of cross-sectional study

Answer 28

• Prevalence of disease is compared based on exposures [Exposed VS Non-exposed]
• Prevalence of exposure is based on diseases [Disease VS No disease]