Normal Test Research Articles

Pengaruh Model Pembelajaran Two Stay Two Stray (TSTS) Terhadap Keterampilan Menyimak Siswa Kelas V Sekolah Dasar

This study aims to determine the effect of using the Two Stay Two Stray (TSTS) learning model on the listening skills of fifth-grade students. The research was conducted in classes VB and VC at UPT SDN 015 Sumber Sari, involving a total of 62 students, during the odd semester of the 2024/2025 academic year, specifically in July 2024. The study utilized a Non-Equivalent Control Group Design, involving two classes: VC as the experimental class with 32 students and VB as the control class with 30 students. In the experimental class, learning was conducted using the Two Stay Two Stray (TSTS) model, while in the control class, conventional teaching methods were applied. Students' listening skills were assessed through pretests and posttests in audio format, each consisting of 20 questions. The data collected were analyzed using normality tests, homogeneity tests, and hypothesis testing through the SPSS 24 application. The results showed that hypothesis testing using the t-test produced a significance value of 0.000 < 0.05, indicating that Ha was accepted and Ho was rejected. These findings suggest a significant effect of applying the Two Stay Two Stray (TSTS) learning model on students' listening skills. This improvement was evident from the average posttest scores, with the experimental class achieving an average of 83.48, higher than the control class's average of 71.74. Thus, this study confirms that the use of the Two Stay Two Stray (TSTS) model is effective in enhancing the listening skills of fifth-grade elementary school students.

The effects of sleep deprivation on the balance system: following normal sleep, 24h of sleep deprivation, and rest under eyes-open and eyes-closed conditions.

This study investigated the effects of sleep deprivation (SD) on balance after normal sleep, 24h of SD, and subsequent rest under eyes-open (EO) and eyes-closed (EC) conditions. Our aim was to ascertain whether the reduced efficiency of balance control following SD is generalized or selective. Nineteen participants (12 females, 7 males) completed the Pittsburgh Sleep Quality Index (PSQI). The mean ages for male participants were 24.14 ± 0.37years, their height was 180.71 ± 5.46cm, and weight of male participants were 81.71 ± 13.42kg. For female participants, the mean ages were 24.41 ± 4.01years, their height was 163.66 ± 2.64cm, and their weight was 59.54 ± 9.18kg. Stance analyses were conducted after normal sleep, 24h of SD, and subsequent rest of both the EO and EC. Participants performed a normal balance test, a second test while holding cubes and counting backwards from 200 by sevens, and a third test after rest under EO and EC. Independent samples t-tests showed significant height and weight differences between sexes (p < 0.05), with females generally smaller. No significant differences were found in age, daytime sleep duration, or PSQI score (p > 0.05). Significant differences in parameters such as length of the minor axis (lomna), angle, and area were observed in EO and EC across the three days, revealing the interplay between visual stimuli, cognitive tasks, and parameter stability. SD has multifaceted impacts on motor and cognitive performance, even when attentional and sensory resources are not strained. Our findings elucidate the nuanced impact of SD on cognitive performance, and suggest the efficacy of external factors in mitigating its effects on postural control.

Pengaruh Model Pembelajaran Project Based Learning terhadap Kemampuan Menulis Cerita Rakyat Kelas V SD Negeri O6 Ladang Padi

This study aims to describe the effect of the Project Based Learning model on the ability to write folk tales among fifth-grade elementary school students. The method used is a quasi-experimental design with a nonequivalent control group design. The subjects of this study were fifth-grade students of SD Negeri 06 Ladang Padi. The sample consisted of two classes: class VA as the experimental group and class VB as the control group. The experimental class implemented the Project Based Learning model, while the control class used a text-based teaching method. The students' ability to write folk tales was measured through a pretest and posttest administered to both groups using the same question, consisting of one item. The statistical data analyzed included normality tests, homogeneity tests, and hypothesis testing, processed using SPSS 23 software. The results showed that the hypothesis test produced a significance value of 0.00 &lt; 0.05, indicating that Ha was accepted and Ho was rejected.The influence of the Project Based Learning model can be seen in the significant improvement in the experimental class. The improvement in students' ability to write folk tales was evidenced by the difference in the average posttest scores between the experimental and control classes. The experimental class achieved an average posttest score of 80.13, while the control class scored 60.12 on average. These findings demonstrate that the implementation of the Project Based Learning model significantly affects the ability to write folk tales among fifth-grade students at SD Negeri 06 Ladang Padi.

Reduction of the Douleur Neuropathique 4 (DN4) Score in the Supraclavicular Nerve Separation and Disability of the Arm Shoulder and Hand (DASH) Score Third Month and Sixth Month Post Open Reduction Internal Fixation of Clavicular Fracture

Introduction: Clavicle fractures are common injuries to the scapular girdle, with fractures in the middle third of the clavicle being the most prevalent. Non-operative treatment is often used but can lead to unsatisfactory outcomes, including pain, malunion, and thoracic outlet syndrome. As a result, operative fixation using Open Reduction and Internal Fixation (ORIF) Plate and Screw (ORIF PS) has gained popularity. Postoperative complications such as numbness around the surgical incision are frequently observed. This study aims to evaluate the differences in functional outcomes in patients with clavicle fractures post ORIF PS using the preserved supraclavicular nerve and non-preserved supraclavicular nerve methods, assessed by the Disability of the Arm Shoulder and Hand (DASH) score and Douleur Neuropathique 4 (DN4) score at 3 and 6 months post-operation. Methods: This cohort study used medical records data from patients with middle third clavicle fractures at RSUP Prof. Dr. IGNG Ngoerah. Patients were divided into two groups: preserved supraclavicular nerve and non-preserved supraclavicular nerve. Data were collected at 3 and 6 months post-operation to evaluate DASH and DN4 scores. Statistical analysis was performed using SPSS version 25.0, with the Kolmogorov-Smirnov test for normality and appropriate hypothesis tests based on data distribution. Results: This study involved 51 patients with clavicle fractures undergoing ORIF PS surgery. There were no significant differences in baseline characteristics between the two groups. At three months, the difference in DN4 scores between the preserved and non-preserved groups was not statistically significant (p=0.347). However, at six months, the preserved group showed significantly lower DN4 scores (p=0.012). The DASH scores at three months showed a significant difference between the two groups (p&lt;0.001), with the preserved group showing better scores. At six months, the difference in DASH scores was not significant (p=0.210). Longitudinal analysis showed significant reductions in DASH and DN4 scores between three and six months in both groups. Discussion: This study demonstrates that preserving the supraclavicular nerve during ORIF clavicle surgery provides significant benefits in reducing neuropathic pain and improving arm function in the long term. These findings support the importance of this approach in clavicle fracture surgeries to reduce complications and enhance functional outcomes. Conclusion: Preserving the supraclavicular nerve during ORIF clavicle surgery can significantly reduce neuropathic pain and improve arm function in the long term. These findings emphasize the importance of this approach in clinical practice to improve patient outcomes following clavicle fracture surgery. Keywords: Clavicular fracture, Douleur Neuropathique 4 score, supraclavicular nerve separation, DN4 score, DASH score, ORIF.

Peningkatan kemampuan representasi matematis siswa melalui model pembelajaran berbasis inkuiri berbantuan software geogebra

The students' inadequate mathematical representation abilities, as seen by their trigonometry learning outcomes, are the driving force for this investigation. This study aims to determine whether using Geogebra software in combination with an inquiry-based learning approach may improve students' mathematical representation skills. Of the seventy students enrolled at SMA Negeri 1 Ketambe, twenty-five students from class X IPA 1 and twenty-five students from class X IPA 2 were assigned to the experimental and control courses, respectively. The second class used a quasi-experimental technique with a pre- and post-test design. Tests used as research instruments. The data analysis methods that were employed were the N-Gain Test, Normality Test, Homogeneity Test, and T-Test. The results of the study on hypothesis testing indicate that an inquiry-based learning model can enhance students' capacity for mathematical representation, and that students who employed this strategy saw higher gains in this capacity than those who received conventional instruction.

Pengaruh Kualitas Pelayanan Dan Citra Yayasan Terhadap Kepuasan Siswa Di Yayasan Pendidikan Islam At-Tadzkir Nur Ghazali

At-Tadzkir Nur Ghazali Islamic Education Foundation is an Islamic education provider institution whose legality is registered in MENKUMHAM No. AHU-0016685.AH.01.04. In 2020, the organization of education under its care includes TPQ, PAUDQU, MDTA, Ponpes At-Tadzkir Nur Ghazali, and junior high schools and vocational schools. The purpose of this study was to determine the effect of service quality and foundation image on student satisfaction. This study uses quantitative descriptive methods with data collection techniques in the form of observation and questionnaires. The population used was 63 students and in withdrawing the sample using a total sample. Furthermore, the data were tested for validity and reliability and carried out normality tests, heteroscedasticity tests, multicollinearity tests. Data analysis was carried out using multiple linear regression equation tests with the results Y = -3.140 + 0.040 + 0.764 which shows that service quality and foundation image simultaneously affect student satisfaction. however, partially service quality has no effect on student satisfaction and foundation image affects student satisfaction.

Research on Production Optimization Based on Simulated Annealing Algorithm and Bayesian Sampling Optimization Model

Simulated annealing algorithm is an optimization algorithm in the field of machine learning that is good at processing high-dimensional complex data and seeking global optimal solutions. In this research, the simulated annealing algorithm is combined with mixed integer linear programming and applied to the production decision optimization scenario. Firstly, the normal distribution and hypothesis testing method and the Bayesian sampling optimization model are used to formulate the corresponding sample sampling scheme. This method provides the most comprehensive possible picture of the yield of a complete batch of parts, semi-finished products, or products with the minimum number of samples and the smallest batch size. Secondly, this paper takes the profit maximization of the enterprise as the objective function to model the production inspection and compensation process of the enterprise and uses the simulated annealing algorithm to solve the corresponding optimal production decision scheme. In general, this research not only expands the application scope of simulated annealing algorithm, but also provides a feasible optimization method and reference for similar multi-objective production decision-making problems.

Efektivitas Online Shop terhadap Kemudahan Belanja Mahasiswa di Yogyakarta

This study aims to examine the influence of Online Shop Effectiveness and Ease of Online Shopping on the shopping experience of students in Yogyakarta. In an increasingly digital era, students, as a group heavily reliant on technology, are opting for e-commerce platforms to fulfill their shopping needs. This research uses a quantitative approach with a sample of 105 students living in Yogyakarta. Data were collected through questionnaires, which were tested using validity, reliability, normality, and hypothesis testing. The results show a significant influence of Online Shop Effectiveness and Ease of Online Shopping on students' satisfaction and convenience in online shopping, with a significance value of 0.00. These findings indicate that factors such as ease of navigation, fast delivery, and flexible payment methods contribute significantly to a positive shopping experience for students. The implications of this research provide insights for e-commerce platform managers to improve their services to meet the growing demand of the student market. This study also contributes to the development of the Technology Acceptance Model (TAM) theory in the context of e-commerce in Indonesia.

Application of Pogil Learning Model Integrated with Local Wisdom to Improve Students' Critical Thinking Skills

This article aims to: 1) Know whether students who learn using the POGIL Learning Model integrated with local wisdom have better critical thinking skills than students who learn with conventional learning. 2) Knowing how much the improvement of students' critical thinking skills in the application of the POGIL Learning Model integrated with local wisdom. This article uses a quantitative approach. The method used is Quasi Experiment Design. This study used a pretest-postest control group design. Data analysis techniques were carried out by analyzing preliminary tests of normality and homogeneity then hypothesis testing and N gain testing using the SPSS program. The results of this study showed the following: 1) The results of the first hypothesis test, namely the independent t test, obtained the results of the price of thit &gt; ttab , namely 2.156&gt;1.671 so that H0 is rejected and Ha is accepted, it can be concluded that critical thinking skills are higher in the experimental class using the POGIL learning model integrated with local wisdom. 2) The second hypothesis test using the N-Gain test obtained the results of the experimental class the average value of the N-gain score for the experimental class (POGIL model) after and before being treated was 57.380 or 57.4% and had an N-gain criterion value of 0.4970 included in the medium criteria and was quite effective.

Marketing Mix Implementation Strategy in Improving Teacher Performance: A Study at State Senior High Schools In Bandung City

This study examines the impact of marketing mix elements (Product, Price, Promotion, Place) on teacher performance in Bandung City’s State Senior High Schools. Using quantitative methods and multiple regression analysis, the findings reveal that Product and Place have the strongest positive influence, while Price moderately contributes, and Promotion shows limited direct impact. Validity, reliability, and normality tests confirm robust data quality. The results emphasize the importance of curriculum innovation, equitable incentives, and quality infrastructure in enhancing teacher performance. Recommendations for holistic improvements in education management are discussed.

FRAUD HEXAGON THEORY AND ACADEMIC FRAUD (COMPARATIVE STUDY ON STUDENT OF STIE SUTAATMADJA AND UNIVERSITI ISLAM SELANGOR)

This research aims to determine the difference in perceptions between STIE Sutaatmadja and University Islam Selangor students regarding the fraud hexagon theory (pressure, opportunity, rationalization, ability, arrogance or ego, and collusion) in academic fraud. The methode used in this research is a quantitative method with comparative studies, the sampling technique used in this research is simple random sampling and the sample criteria selected were students from STIE Sutaatmadja and University Islam Selangor. The data collection method used was a questionnaire method in the form of a questionnaire distributed via google form which was analyzed using IBM SPSS Statistic 25. The data analysis technique was the classic assumption test (normality test and homogeneity test) and the independent simple t-test and the men whitney non parametric test. The results of the research show that (1) there is a diffierence in perception regarding the pressure for academic cheating between STIE Sutaatmadja dan University Islam Selangor, there is no different perception regarding the opportunity (2), the rationalization (3), the ability (4), the arrogance (5), Collusion (6) and the academic cheating (7) for academic cheating between STIE Sutaatmadja and University Islam Selangor.

Comparison of Students' Mathematical Communication Ability Between Think Pair Share and Numbered Head Together Cooperative Learning Model

&lt;em&gt;This study aimed to find out the comparison between students' mathematical communication ability taught by Think Pair Share and Numbered Head Together cooperative learning model. The population in the study were all students in grade X MAN 2 Model Medan. The sample were all students of class X-C with 37 students as experimental class I and class X-H with 36 students as experimental class II, which were selected through random sampling technique. The experimental class I was taught by Think Pair Share cooperative learning model while the experimental class II with Numbered Head Together cooperative learning model. This research was quasi experimental with posttest only control group design. Data collection instrument used was mathematics communication ability test that have been tested for validity and reliability. Before testing the hypothesis, normality test was carried out using Shapiro-Wilk test and homogeinity test using Levene test on the research data. The results showed that the samples came from normal and homogeneous distributed population. Hypothesis testing with t-test show that t_count&amp;gt;t_table(2,4 &amp;gt; 1,666). Thus H_0 is rejected and H_1 is accepted, so students’ mathematical communication ability taught by Think Pair Share cooperative learning model is better than the students’ mathematical communication ability taught by Numbered Head Together cooperative learning model.&lt;/em&gt;

Behavior and management of thrips population using biorational insecticides in avocado (Persea americana MILL.) trees

Objective: To evaluate the effectiveness of biorational insecticides to control thrips and to provide alternatives that reduce the negative environmental impact of chemical pesticides on the management of avocado tree. Design/Methodology/Approach: Using a randomized complete block design with four replicates, the following five treatments were evaluated: T1) control (water); T2) chicalote (Argemone mexicana L.) extract; T3) neem (Azadirachta indica) oil extract; T4) potassium soap (potassium salts); and T5) Spinosad (Spinosyn A and Spinosyn D). Each product was applied in its own row. Treatment rows were separated by a row of trees to which no treatment was applied. Samples were taken in different dates from plant and floral sprouts of four randomly selected avocado trees. Each tree was an experimental unit. Results: The data obtained did not comply with the normality test and the homogeneity of variance; consequently, the data were subjected to a General Additive Model (GAM). The most efficient treatments were neem oil extract and Spinosad. Study Limitations/Implications: Different orchards, with different initial pest populations, should be evaluated to determine the level of infestation in which the application of biorational products is still feasible for pest control. Findings/Conclusions: Plant extracts have high potential to control thrips in open-air avocado plantations; consequently, they could be an alternative to the application of synthetic insecticides for pest management.

Experimental repurposing of metformin for Crohn’s disease in trinitrobenzene sulfonic acid induced colitis model in BALB/c mice

Background: Inflammatory bowel disease (IBD) is characterized by repetitive episodes of inflammation of the gastrointestinal tract caused by an abnormal immune response to gut microflora. It includes two types: Ulcerative colitis (UC), which causes widespread colon inflammation, and Crohn’s disease (CD). The current therapy focuses on symptom relief and provides inadequate maintenance of remission and quality of life improvement. Metformin has already been repurposed in few studies with dextran sulphate sodium (DSS) induced colitis. We aimed to evaluate the effect of metformin in TNBS induced acute on chronic colitis, to mimic the relapsing-remitting nature of CD in humans, which has not been done before. Methods: Objectives were, phase I- evaluation of the effect of metformin in TNBS induced acute colitis in BALB/c mice. Phase II- evaluation of the effect of metformin in TNBS induced chronic colitis in BALB/c mice. Phase III- Evaluation of the effect of metformin in TNBS induced acute on chronic colitis in BALB/c mice. Materials And Methods: Trinitrobenzene sulfonic acid (TNBS) was used for inducing both acute, chronic and acute on chronic colitis in BALB/c mice. 36 BALB/c mice were divided into 4 groups i.e. normal control, disease control, positive control and test drug. Effect on DAI score, lower colon weight by length ratio, macroscopy and histopathology were assessed. Results: Metformin showed significant improvement (p&lt;0.05) in all the variables assessed i.e. reduction of (Disease Activity Index) DAI score, lower colon weight by length ratio, lower colon macroscopic score and lower histopathological score in comparison to the disease control group in all the phases i.e. acute (day 5), chronic (day 22) and acute on chronic (day 25). However, the effects were comparable to the positive control. Conclusions: Metformin has potential to be repurposed for Crohn’s disease as it showed comparable efficacy in all three phases.

Evaluation of interproximal and occlusal contacts of single posterior implant-supported restorations fabricated using different CAD software programs: A clinical study

The accuracy of the interproximal and occlusal contacts of single posterior implant-supported restorations designed using computer-aided design (CAD) software programs remains uncertain. The aim of this clinical study was to assess the interproximal and occlusal contacts of single posterior implant-supported restorations designed with 2 distinct dental CAD software programs. Forty single posterior implant-supported restorations were evaluated for interproximal and occlusal contacts. Restorations were designed with 2 CAD software programs (exocad and Dental System) by using the same digital scan and milled with the same milling machine and material. Two study groups were formed according to the CAD software program used (n=20). Dental floss, 12-µm shimstock, the OccluSense device, and the Medit occlusion analyzer app were used to evaluate the interproximal, static, and dynamic occlusal contacts. The Shapiro-Wilk normality test was used, and the Z-test was used to compare the results (α=.05). The interproximal and static occlusal contacts were statistically more accurate when using the Dental System 3Shape software program than the exocad software program (P<.05). No statistically significant difference in the dynamic occlusal contact was found between the 2 studied groups (P=.147). The accuracy of interproximal and occlusal contacts of single posterior implant-supported restorations differed depending on the CAD software program used. The Dental System 3Shape software program demonstrated more accurate interproximal and static occlusal contacts than the exocad software program.

PENGARUH CITRA MEREK, BIAYA PENDIDIKAN DAN KUALITAS LAYANAN TERHADAP KEPUASAN ORANG TUA SISWA

This research aims to determine whether there is an influence of brand image, education costs, and service quality on the satisfaction of parents of students at SMK Ar-Raudhah North Jakarta. Using a quantitative descriptive research method with primary data obtained from distributing questionnaires to 170 parents of students. The questionnaire data were analyzed using validity tests, reliability tests, classical assumption tests, normality tests, and multiple regression analysis. The research results indicate that 1) brand image partially has a positive and significant effect on parent satisfaction; 2) education costs partially do not have a positive and significant effect on parent satisfaction; 3) service quality partially has a positive and significant effect on parent satisfaction; and 4) there is a positive and significant simultaneous effect of brand image, education costs, and service quality on parent satisfaction.

PENGARUH CUSTOMER RATING, CUSTOMER REVIEW DAN KEPERCAYAAN TERHADAP MINAT BELANJA DARING PADA MARKETPLACE SHOPEE

The purpose of this study is to determine the influence of customer ratings, customer reviews, and trust, both partially and simultaneously, on online shopping interest in the Shopee marketplace. This study employs a quantitative descriptive method. The population of this study consists of employees of PT. Pangansari Utama Food Resources, totaling 108 individuals with a sample size of 85 individuals. Data collection was carried out through survey data using a questionnaire as a tool. The data analysis techniques include validity tests, reliability tests, normality tests, heteroscedasticity tests, autocorrelation tests, multicollinearity tests, multiple linear regression analysis, hypothesis testing, and the coefficient of determination. The research results indicate that there is an influence of customer rating, customer review, and trust on online shopping interest in the Shopee marketplace. The customer rating variable has a partial effect on online shopping interest. The customer review variable also has a partial effect on online shopping interest. The trust variable does not have a partial effect on online shopping interest. Based on data analysis, it was found that online shopping interest is simultaneously influenced by customer rating, customer review, and trust by 77.7%, while the remaining 22.3% is influenced by other variables not examined in this study.

PENGARUH PROMOSI DAN PRODUK PEMBIAYAAN DANA MOBIL TERHADAP VOLUME PENJUALAN PT MNC FINANCE

Marketing management plays an active role in increasing sales volumes through the variables that influence it, including products and promotions. The purpose of this research is to find out the impact of the products and promotions of Dana Mobil on sales volume as well as whether the products and promotions of Dana Mobil simultaneously influence the sales volume of the MNC Finance. This research is descriptive quantitative research. Research is done by looking for primary data through a questionnaire. The data collected was then processed with statistical analysis using validity tests, realism tests, normality tests, heterocadastism tests, multicolinerity tests, auto-correlation tests, double linear regression analyses, hypothetical tests, and double coefficients. The results of the research showed that product variables had no influence and did not significantly increase sales volumes. As well as promotional variables, they have a positive and significant impact on increased sales volumes. Additionally, product and promotion variables have a simultaneous and significant influence on sales volumes.

The Impact of Listening Comprehension on Reading Comprehension: A Correlational Research

The aim of this research was to find out whether or not there was any correlation between students reading comprehension and students listening comprehension. The population was the tenth-grade students with the total 630 students from 14 classes at SMA N 10 Palembang. To the sample of this research, intake sampling technique was implemented. There were 90 students as a sample from class X.7 and X.8. The data were selected from students reading comprehension and students listening comprehension. In analysing the data, correlation analysis, regression analysis and normality test was used. Based on the statistical, it was found that the correlation coefficient or the R-value (0.000) with significant coefficient (p-value) was 0.422, which was higher than 0.05. It means that significant value (2-tailed) was higher than alpha value (0.422&gt; 0.05). It could be concluded that there was a significant correlation between students' reading comprehension and listening skill. Since the Pearson correlation coefficient was 0.000, it indicated that there was correlation between students' reading. Also, for the contribution of listening comprehension to reading comprehension it was only 17.8%. It means that listening comprehension has no influence to reading comprehension. In conclusion, the findings indicate that students who have high listening comprehension does mean that they will also have good reading comprehension. Also, reading comprehension can be used to help listening skills because listening is the ability to capture sounds, complete, speak, syntax, jargon, and obtain data.

ANALYSIS EFFECT OF EXPORTS, IMPORTS, INFLATION AND FOREIGN DEBT ON FOREIGN EXCHANGE RESERVES IN INDONESIA

The purpose of this study was to test and analyze how Indonesia's foreign exchange reserves were affected by imports, exports, inflation, and foreign debt. Regarding the relationship between Indonesia's foreign exchange reserves and imports, exports, inflation, and foreign debt for the 2019–2023 timeframe, there is a gap between theory and empirical data, which makes this study noteworthy. In order to regulate it and preserve economic stability, it is crucial to constantly track the movement of foreign exchange reserves. Data for the study were taken from official publications of Bank Indonesia (BI), the Central Statistics Agency (BPS), and the Indonesian Economic and Financial Statistics (SEKI). Monthly data was gathered for the study between 2019 and 2023. Using time series data for the 2019–2023 period, including monthly data and up to 60 series data, the sampling was carried out in Indonesia. using conventional hypothesis testing (t, f, and determination tests) and assumption checking (multicollinearity, normality, and heterokedasitas tests) to estimate multiple linear regression. While imports, exports, inflation, and foreign debt are independent factors, foreign exchange reserves are the dependent variable. The results of the study show that the dependent variable is influenced by two independent variables. Foreign exchange reserves are positively impacted by exports, but negatively by inflation. Furthermore, imports and foreign debt have no effect on foreign exchange reserves, making them independent variables that do not affect the dependent variable.