What is Longitudinal: Definition and 143 Discussions

A longitudinal study (or longitudinal survey, or panel study) is a research design that involves repeated observations of the same variables (e.g., people) over short or long periods of time (i.e., uses longitudinal data). It is often a type of observational study, although they can also be structured as longitudinal randomized experiments.Longitudinal studies are often used in social-personality and clinical psychology, to study rapid fluctuations in behaviors, thoughts, and emotions from moment to moment or day to day; in developmental psychology, to study developmental trends across the life span; and in sociology, to study life events throughout lifetimes or generations; and in consumer research and political polling to study consumer trends. The reason for this is that, unlike cross-sectional studies, in which different individuals with the same characteristics are compared, longitudinal studies track the same people, and so the differences observed in those people are less likely to be the result of cultural differences across generations. Longitudinal studies thus make observing changes more accurate and are applied in various other fields. In medicine, the design is used to uncover predictors of certain diseases. In advertising, the design is used to identify the changes that advertising has produced in the attitudes and behaviors of those within the target audience who have seen the advertising campaign. Longitudinal studies allow social scientists to distinguish short from long-term phenomena, such as poverty. If the poverty rate is 10% at a point in time, this may mean that 10% of the population are always poor or that the whole population experiences poverty for 10% of the time.
When longitudinal studies are observational, in the sense that they observe the state of the world without manipulating it, it has been argued that they may have less power to detect causal relationships than experiments. However, because of the repeated observation at the individual level, they have more power than cross-sectional observational studies, by virtue of being able to exclude time-invariant unobserved individual differences and also of observing the temporal order of events. Some of the disadvantages of longitudinal study are that they are time-consuming and expensive. Therefore, they are not convenient.Longitudinal studies can be retrospective (looking back in time, thus using existing data such as medical records or claims database) or prospective (requiring the collection of new data).Cohort studies are one type of longitudinal study which sample a cohort (a group of people who share a defining characteristic, typically who experienced a common event in a selected period, such as birth or graduation) and perform cross-section observations at intervals through time. However, not all longitudinal studies are cohort studies, as longitudinal studies can instead include a group of people who do not share a common event.Longitudinal studies do not require large numbers of participants (as in the examples below). Qualitative longitudinal studies may include only a handful of participants, and longitudinal pilot or feasibility studies often have fewer than 100 participants.

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  1. P

    How Does Longitudinal Stress Affect a Body's Internal Tension?

    Stress = F(restoring)/ Cross sectional area Stress = 2F/A
  2. C

    I Longitudinal DIS Structure functions

    DIS observables can be expressed in terms of structure functions F1, F2 and FL. There exists the relation ##F_L = F_2 - 2xF_1##. We can write $$ F_L = \sum_a x \int_x^1 \frac{dy}{y} C_{a,L}(y,Q) f_a (\frac{x}{y},Q) $$ and similarly for ##F_1## and ##F_2##: $$ F_1 = \sum_a x \int_x^1...
  3. Z

    I Longitudinal waves on a string

    Good day to everyone, I kindly ask for your help. My question is: "Does a string have to be under tension, to transmit longitudinal waves? Why is it so?" I have trouble finding relevant scientific articles regarding the question and for reasearching "longitudinal waves on a string". If anyone...
  4. T

    Amplitudes of longitudinal sound waves

    I'm coming back to physics after a long so apologies if this has a basic answer- How can the amplitude of a longitudinal sound wave be increased without increasing its wavelength? I understand what it would look like graphically if a low amplitude sine wave and high amplitude sine wave were...
  5. A

    EM waves, longitudinal EM propagation?

    Hey, after doing some reading I stumbled across a few fundamental questions.1) Do all EM waves across the EM spectrum , if they travel through space have their E field and B field amplitudes exactly equal and in phase and shifted 90 degrees from one another? If the answer is yes then... 2) In...
  6. A

    A Average transverse momentum as a function of the longitudinal momentum

    Hello everybody! I am working on a code in which I need to study the dependence of ##<p_T>## vs ##p_L## (the average transverse momentum and the longitudinal momentum of a particle). I am looking for references, papers, books, etc. concerning this topic, but I have not been so lucky. My...
  7. lLehner95

    Longitudinal distribution for a neutrino beam

    In the center of mass frame of reference i found that ##p^{*}=\frac{[(M^{2}-m_{\nu}^{2}-m_{K}^{2})^{2}-4m_{\nu}^{2}m_{K}^{2})]^{1/2}}{2M}##. I don't know how to find the momentum distribution ##p_{L}(\theta)## considering that i have 2 different mesons with a specific number ratio...
  8. Skrphys

    Electricity: Is it a longitudinal wave?

    I am a high school teacher and we were discussing waves and electricity in class today. One of my students asked me if electricity is a longitudinal wave or not and I had no idea how to answer. So, I realize that electric fields are what drive electrons to move through conducting wires, but...
  9. OmerKocak

    I In NMR, Why does longitudinal magnetization decrease when....

    *** Answered off site. No need for further explanation. *** I am trying to understand MR Imaging physics. In NMR, when you put some energy in a system with a static longitudinal net magnetization, you create a transverse component and the longitudinal component decreases (in other words, net...
  10. Samuel Williams

    Are longitudinal magnetic waves possible?

    Homework Statement Are longitudinal magnetic waves possible? Give reasons for your answer. Homework Equations Working with Maxwell's equations, Lorentz force, electrostatic and electromagnetic waves in plasma. The Attempt at a Solution No idea whatsoever. I believe it is possible based on...
  11. B

    B Why longitudinal waves are waves?

    i know it's an absurd question, but why are longitudinal waves called waves although they aren't wave-like?
  12. Arka sarkar

    Longitudinal Wave Velocity: Why it's Greater in Solids

    Why the velocity of longitudinal wave in solid is greater than transverse wave
  13. R

    Light waves through polarizers: transverse or longitudinal?

    A question about the light-waves and the double-slit experiment: Light can be polarized: If you turn a polarization sheet in a polarized beam of light, you can see that polarized light has an angle. So the light-wave is transverse (right?) But how does a transverse wave ‘bend’ as it goes...
  14. B

    Extension of a rod segment dx due to a passing longitudinal wave

    Let us look at short segment of a rod with its length dx. Due to longitudinal wave, left endpoint moves for s in the direction of x-axis and the right endpoint moves in the same direction for s+ds. Because I want to calculate the elastic energy of the wave motion, I need the extension of dx so...
  15. B

    Calculating the speed of longitudinal wave

    Homework Statement I didn't quite understand my professor when he defined the speed of longitudinal wave. Lets say I have a slinky and on one side we act with a force F along the slinky. Well, he said that this part then starts to move with velocity v. But how? v isn't constant... Homework...
  16. K

    Superposition on longitudinal wave

    When a spring is fixed at both ends and it is vibrating back and forth, reflection will occur. So where are the nodes and antinodes? Are they at compression or rarefaction region?
  17. K

    Understanding the Longitudinal Wave Velocity of a Helical Spring

    v = [sqrt(D/m)] * L, where D is spring constant, m is mass of spring, L is length of the spring My lecturer give me this formula to find the longitudinal wave velocity on an helical spring. May i know how to derive this formula? < Mentor Note -- this is not technically a homework question, but...
  18. K

    A Longitudinal and transverse response function

    I was reading the book "finite temperature field theory" (https://www.amazon.com/dp/0521820820/?tag=pfamazon01-20) and encountered a problem on page 111 about linear response theory. Consider a system with some conserved baryon matter perturbed by a source J_\mu, coupled to the baryon current...
  19. S

    Amplitude and wavelength of longitudinal wave

    Homework Statement A wave is shown below. The dots represent the particles of the wave at a time t = 0 s, and the vertical lines represent the positions of the particles before the wave arrives. Find the amplitude and wavelength of the wave Homework Equations Not sure The Attempt at a...
  20. E

    I Longitudinal resistivity in Integer Quantum Hall Effect

    I have studied the integer quantum hall effect mainly from David Tong's notes and i understand how the ## \rho_{xy}## is quantized in terms of the chern number. What I don't understand is - how the chern numbers relate to the number of filled Landau levels though. - I also don't understand the...
  21. FallenApple

    A Leaving out a confounder in longitudinal regression?

    Say I want to analyze how a relation changes though time. Like usual, I would throw in the potential confounders into the regression model. But what if some of the confounders are not determined at the beginning of the study but at some point within time? For example, say I want to analyze the...
  22. M

    I Is the F-test Calculation Different for Longitudinal Data in Linear Regression?

    Can i Use a standard F-test on longitudinal data for a linear multiple regression? Mons
  23. K

    What is the frequency of a longitudinal wave in terms of distance and speed?

    Homework Statement A longitudinal wave is propagated through a medium. The distance from one max compression to the next is X meters, and its speed is Y m/s. Express the frequency of the waves in terms of x and y. Homework Equations velocity of a wave= Wavelength x Frequency Velocity of a wave...
  24. John Doe

    I Amplitude of particles in the medium of a longitudinal wave

    I was thaught you can create a sinusoidal wave by making a source oscillate with simple harmonic motion in a medium, such as moving one end of a rope up and down to create a periodic transverse wave. For transverse waves, it is easy to see that every particle in the rope moves up and down with...
  25. A

    The longitudinal displacement of sound wave

    Homework Statement The longitudinal displacement of a mass element in a medium as a sound wave passes through it is given by s = sm cos (kx – ωt). Consider a sound wave of frequency 330 Hz and wavelength 0.95 m. If sm= 16 µm, what is the displacement of an element of air located at x = 1.1 m...
  26. B

    Longitudinal and Transverse waves transmitting at same Veloc

    Homework Statement A picture of the problem can be found here: https://gyazo.com/a92447dcfebed53d4cbd12fc94300d9c[/B] Homework Equations So, I've already finished part A. For part B, I'm trying to figure out how to equate the two with mass on either side of the equation so that I can solve for...
  27. A

    I Longitudinal Waves: Compression & Rarefaction

    In a longitudinal wave is a compression pulse always followed by a rarefaction on its tail
  28. G

    I Breakthrough Starshot: 1st Macroscopic Test of Longitudinal Acceleration

    Breakthrough Starshot is an ambitious project that aims to use a superlaser to push a tiny craft up to 0.2 c https://en.wikipedia.org/wiki/Breakthrough_Starshot At such speeds, it would be possible to perform a macroscopic test of the longitudinal acceleration, provided the craft has an...
  29. prashant singh

    I Why on Earth's surface, longitudinal or merediance lines are perpendicular to equatorial line?

    I think its a defination to have infinite longitudnal lines , if line are not perpendicular than the infinite point will not add up to give the circumferance of equator, please help
  30. A

    B Exploring Waves: Understanding What a Wave Is Made Of

    I'm going to begin studying about waves and sounds. But before I start I wanted help in understanding what really a wave is, I searched on google and YouTube and what I did understand was that waves are caused by a disturbance, due to that disturbance the potential energy gets converted to...
  31. Z

    How is longitudinal wave spread

    Homework Statement How is longitudinal wave spread? http://s11.postimg.org/pm7hxibo3/vala.png Here is how the transverse wave is spread in T/4, T/2, 3T/4, T (T- period) I need the same graph for the longitudinal wave. Homework Equations X=c*T (c-velocity of moving of the wave) The Attempt at...
  32. E

    Young's equation and longitudinal waves

    Hi I have learned at school that we can use Young's equation Lambda = ax/D to calculate the wavelength of light from an interference pattern I'm wondering if this equation also works for longitudinal waves? Thank you for your help
  33. muscaria

    Longitudinal waves and vector potentials.

    Hello, I was wondering if anybody knew of any material (books, papers etc..) which considers a possible connection between longitudinal waves and vector potentials, at least mathematically. I have been scouting about, but failed to find anything substantial. I understand that there seems to be...
  34. A

    I Way of producing 600kHz longitudinal waves - Piezo or siren

    Hello! My name is Nick and I have an MSc in Computer Science, I'm also Physics enthusiast and amateur/independent researcher. I would like to ask for your help on something. I'm currently trying to find a way to study ultrasonic waves' effects on water and I'd like to find a means of...
  35. G

    Spotting Errors in Transverse & Longitudinal Accelerations

    Let's say you know all 3 cartesian components of a particle's velocity and all 3 for it's acceleration. You can split the acceleration vector into two vectors, one parallel (longitudinal) to the velocity vector and one perpendicular (transverse) to the velocity vector. Then, I found the...
  36. S

    Thermal Equilibrium and Longitudinal Relaxation

    Homework Statement Problem 6.2 from Magnetic Resonance Imaging: Physical Principles and Sequence Design. Show that M_o \approx \rho_o \frac{s(s+1)\gamma^2\hbar^2}{3kT}B_o Homework Equations M_o = \rho_o \gamma \hbar \frac{\sum m_s e^{m_s(\hbar w_o / kT)}}{\sum e^{m_s(\hbar w_o / kT)}} ...
  37. N

    How to draw longitudinal lines on a circle as Earth?

    I have a circle, representing Earth with equator drawn on it. I need to draw longitudinal lines on 15 degree, 30 degree, and 60 degrees distance? I am not sure how and from where to measure these angular distances. Thanks.
  38. B

    Charpy Test for the Longitudinal Weld Seam of Steel Pipe

    Hi all We are currently conducting Charpy V Notch Test to the Longitudinal Weld Seam of a Steel Pipe. The specimens we have tests are of two different size : full size (10mm x 10mm x 55mmL) and 2/3 size (6.7mm x 10mm x55mmL). We have conducted the tests severally time at -30degC. The results...
  39. N

    Mechanical / progressive / transverse / longitudinal waves

    Correct me if I'm wrong, but based on what I've learnt, there are three kinds of waves: mechanical, transverse progressive and longitudinal progressive. Mechanical - A disturbance makes particles vibrate on the spot Transverse progressive - Energy is carried, and moves perpendicular to the...
  40. C

    Finding the Longitudinal Force: A Scientific Approach

    Homework Statement Very long thread, with constant longitudinal charge Q' is placed in a vacuum parallel to a very long conductive strip, whose width is a. thread is placed in the middle of the strip and it's a/2 away from it, if the surface density of charge of the strip is σ, find the...
  41. bananabandana

    Longitudinal Wave Equation from Transverse One

    Homework Statement Please see attached. Part ii) Homework EquationsThe Attempt at a Solution So I try to conserve volume as it suggests in the hint. I take the initial volume of the region to be given by: $$ h \times \delta x \times l = (\delta x + \eta) (h+\Psi) l $$ Where l is just some...
  42. R

    Maxwell's equations and longitudinal waves

    Hi guys, I am having hard times in understanding whether or not the longitudinal electromagnetic waves are solutions to Maxwell's equations. In Cohen-Tannoudji "Introduction to QED" it's stated that by writing the fields as the sum of a longitudinal and transverse part one can show that waves...
  43. R

    Vehicle COG comparison for longitudinal rollover

    Hi I am trying to compare which of the (2) models has the greatest stability longitudinaly. I have the COG height and longitudinal (axle split) Model A has it COG closer to the centre of the axles (longitudinal - further from rear axle 1,487l) but sits much higher (2,537 above axle centre) Model...
  44. M

    What will happen if light is longitudinal wave?

    Topic edited by mfb (original was "What will happen if light is transversal wave? ") Will people see the world in a completely different view?
  45. F

    Choose the correct snapshot graph longitudinal waves

    Homework Statement http://i.imgur.com/4dL6TQY.jpg I don't know how to read the figure or the graphs. O_O
  46. Einj

    Longitudinal and transverse phonons velocities

    Hello everyone! Does anyone know how to extract the velocities of longitudinal and transverse phonons starting from their Lagrangian and/or equation of motion? Thanks!
  47. J

    Transverse and longitudinal electric Green function

    Hello everyone: This is what I read in a paper, the spontaneous emission rate written by Fermi's Golden Rule is just related to the local transverse electric field. Dose anyone can explain to me what's the meaning of "transverse mode" here? Why the emission is not related to longitudinal...
  48. C

    Longitudinal polarization in Feynman photon propagator?

    For internal photon states, is it necessary to sum over the longitudinal polarization state in addition to the transverse states? And if so, does the ordinary Feynman-gauge propagator take care of this? Thanks!