Understanding Study Designs: Descriptive vs. Analytical and Their Uses, Lecture notes of History of War

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ACKNOWLEDGMENTS

TEAM LEADER

SARAH ALENEZY

TEAM MEMBERS

MAJD ALBARRAK

NOUF ALOTAIBI

REVIEWER

Yazeed Al-Dossare

KSU COLLEGE OF MEDICINE

INTRODUCTION TO

STUDY DESIGNS

STUDY DESIGNS PAGE 02

TABLE OF CONTENTS

STUDY

DESIGNS

INTRODUCTION

SPOTTING OF

THE STUDY

DESIGN

STUDY

DESIGN

TREE

TYPES OF

STUDIES

Original, refrased. Our notes. Doctors notes. Golden notes.

LECTURE OBJECTIVES

By the end of this lecture, I am able to:

List differences between descriptive and analytical study designs

Describe main types of study designs and their uses

Identify different study designs with examples

QUIZ

Study Design Tree

All Studies

Analytical (PICO)

Descriptive (PO)

Case Report Experimental Observational

Case Series

Cross-Sectional (Survey)

Qualitative

Randomized Clinical

Trials (RCTs)

Group Data

Individual

Ecological Study

Cross-Sectional (Analytical)

Cohort

Case-Control

Hypothesis

Generate Test

Whether a study is hypothesis-testing or hypothesis-generating, that depends on:

1. Sequence of past studies.

2. Present state of knowledge (i.e. Whether a hypothesis currently under evaluation was suggested by a previous study).

Sequence Of Study Design

Analytical-Observational CASE-CONTROL Evaluate if hypothesized exposure is related to the outcome of interest

Analytical-Observational COHORT Further define importance of exposure for the development of outcome

Analytical-Experimental RCT Test the actual link between exposure and outcome. i.e. Causality

Increasing Knowledge of Exposure / Outcome (Strength of Evidence)

DESCRIPTIVE

Identifying hypotheses to test in analytic studies

● If one seeks to identify the etiologic factors (e.g. hyperlipidemia/any causal factor) behind an outcome (e.g. an MI),

then, each step in the epidemiologic framework provides new and important information.

● Descriptive studies identify hypotheses to test in analytic studies.

● Case-control studies are then usually applied to evaluate if the hypothesized exposure is related to the

outcome of interest.

● Subsequently, cohort or longitudinal studies are applied to further define the importance of exposure to the causal

agent for the development of the outcome.

Study Design Distinctive Factors

Two important distinctive factors in study designs:

1. Quantification of relationship between exposure and outcome..

2. Researcher assignment (manipulation) of exposure.

Quantification Of The Relationship

no

yes

Descriptive

Analytical

Assignment Of The Exposure By Researcher

Yes

No

Experimental (RCT)

Observational

TYPES OF STUDIES

USES, COMPARISONS & EXAMPLES

Descriptive Studies

Case Report Case-Series Cross-Sectional (Survey) Qualitative

Single case (^) similar cases Collection of

Single sample from larger population (No comparison)

Process of naturalistic inquiry that seeks in-depth understanding of phenomena within their natural setting (Individual, societies, languages)

● Detailed report of the symptoms, signs, diagnosis, treatment, and follow-up of an individual patient.

● Typically an unusual/novel occurrence

Detailed report of the symptoms, signs, diagnosis, treatment, and follow-up of a group of patients or cases with similar issue.

● Study prevalence of health related events at a point in time/snapshot.

● Often used to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions)

Answers the 'why?' questions

● Detecting novelties.

● Generating hypotheses.

● Allowing in-depth understanding.

● Educational value.

● Useful for hypothesis generation.

● Informative for very rare disease with few established risk factors.

● Cheap and simple.

● Ethically safe.

● Provides depth and detail

● Creates openness

● Simulates people’s individual experiences

● Lack of ability to generalize

● No possibility to establish cause-effect relationship

● Publication bias

● Cannot study cause and effect relationships

● Cannot assess disease frequency

Not suitable for studying rare or highly fatal diseases or a disease with short duration

● Usually fewer people studied

● Less easy to generalize

● Dependent on skills of the researcher

Population

Primary Use

Advantages

Disadvantages

SPOTTING OF THE STUDY DESIGN

All Studies

Analytical (PICO)

Descriptive (PO)

Case Report Experimental Observational

Case Series

Cross-Sectional (Survey)

Qualitative

Randomized Clinical

Trials (RCTs)

Group Data

Individual

Ecological Study

Cross-Sectional (Survey)

Cohort

Case-Control

Question 1

3 Issues Of The Design Tree

Question 2

Question 3

The type of study can be spotted by looking at three issues as per the “Design Tree”:

Q1 What was the aim of the study?

1. To simply describe a population (PO questions) → Descriptive

2. To quantify the relationship between exposure & outcome (PICO questions) → Analytic

Q2 If analytic, was the intervention randomly allocated (assigned by the researcher)?

1. Yes → RCT

2. No → Observational

Q3 If Observational, When were the outcomes determined (measured)?

1. Some time after the exposure (intervention) è Cohort study

2. At the same time as the exposure (intervention) è Cross-sectional

3. Before the exposure was measured è Case-Control

EXAMPLES

“Primary spontaneous pneumothorax is a common disorder occurring in young adults without underlying

lung disease. Although tobacco smoking is a well-documented risk factor for spontaneous pneumothorax, an

association between electronic cigarette use (that is, vaping) and spontaneous pneumothorax has not been

noted. We report a case of spontaneous pneumothoraces correlated with vaping”

Study design: Descriptive – Case Report

“Fourteen patients were treated for electronic cigarette burns between 2012 and 2016. Burn size ranged from

<1% to 6% total body surface area. Most patients suffered burns to their thighs because the battery or device

exploded in their pocket. The majority suffered partial thickness burns while four patients had full thickness

burns. Three patients required excision and autografting, all of which were full thickness burns. The average

time to recovery was 24.5 days”

Study design: Descriptive – Case Series

“We conducted 12 focus groups and two individuals interviews with youg adult nonusers e-cigarette vapers,

cigarette smokers, and dual users to assess beliefs about the effects of e-cigarettes. After a series of

open-ended questions,follow-up questions assessed reactions to domains previously examined in

expectancy measures for cigarette smoking and e-cigarette vaping. The constant comparative method was

used to derive themes from transcripts”

Study design: Descriptive - Qualitative

“A survey of 6902 German students (mean age 13.1 years, 51.3% male) recruited in six German states was

performed. Exposure to e-cigarette advertisements was measured with self-rated contact frequency to three

advertising images. Multilevel mixed-effect logistic regression models were used to assess associations

between exposure to e-cigarette advertisement and use of e-cigarettes, combustible cigarettes and hookahs

(ever and past 30 days)”

Spot the design! Three questions:

Q1: Analytical (association)

Q2: Observational (exposure was not randomly allocated)

Q3: Cross-sectional (Exposure & Outcome at the same time)

“Adult smokers (≥18 years old) making thewir first purchase at local participating

vape shops were asked by professional retail staff to complete a form with their

basic demographic and smoking history details together with scoring of their level

of nicotine dependence by a questionnaire. Participants were instructed how to

charge, fill, activate and use their e-cigs. Key troubleshooting was addressed and

phone numbers were supplied for technical assistance. Participants were

encouraged to use these products in the anticipation of reducing the number of

cig/day smoked. Their cigarette consumption was followed-up at 6 and 12 months”

Spot the design! Three questions:

Q1: Analytical (association)

Q2: Observational (exposure was not randomly allocated)

Q3: Cohort study (Exposure is measured BEFORE Outcome is measured)